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  1. 03 8月, 2017 1 次提交
    • M
      mm, mprotect: flush TLB if potentially racing with a parallel reclaim leaving stale TLB entries · 3ea27719
      由 Mel Gorman 提交于 
      Nadav Amit identified a theoritical race between page reclaim and
mprotect due to TLB flushes being batched outside of the PTL being held.

He described the race as follows:

        CPU0                            CPU1
        ----                            ----
                                        user accesses memory using RW PTE
                                        [PTE now cached in TLB]
        try_to_unmap_one()
        ==> ptep_get_and_clear()
        ==> set_tlb_ubc_flush_pending()
                                        mprotect(addr, PROT_READ)
                                        ==> change_pte_range()
                                        ==> [ PTE non-present - no flush ]

                                        user writes using cached RW PTE
        ...

        try_to_unmap_flush()

The same type of race exists for reads when protecting for PROT_NONE and
also exists for operations that can leave an old TLB entry behind such
as munmap, mremap and madvise.

For some operations like mprotect, it's not necessarily a data integrity
issue but it is a correctness issue as there is a window where an
mprotect that limits access still allows access.  For munmap, it's
potentially a data integrity issue although the race is massive as an
munmap, mmap and return to userspace must all complete between the
window when reclaim drops the PTL and flushes the TLB.  However, it's
theoritically possible so handle this issue by flushing the mm if
reclaim is potentially currently batching TLB flushes.

Other instances where a flush is required for a present pte should be ok
as either the page lock is held preventing parallel reclaim or a page
reference count is elevated preventing a parallel free leading to
corruption.  In the case of page_mkclean there isn't an obvious path
that userspace could take advantage of without using the operations that
are guarded by this patch.  Other users such as gup as a race with
reclaim looks just at PTEs.  huge page variants should be ok as they
don't race with reclaim.  mincore only looks at PTEs.  userfault also
should be ok as if a parallel reclaim takes place, it will either fault
the page back in or read some of the data before the flush occurs
triggering a fault.

Note that a variant of this patch was acked by Andy Lutomirski but this
was for the x86 parts on top of his PCID work which didn't make the 4.13
merge window as expected.  His ack is dropped from this version and
there will be a follow-on patch on top of PCID that will include his
ack.

[akpm@linux-foundation.org: tweak comments]
[akpm@linux-foundation.org: fix spello]
Link: http://lkml.kernel.org/r/20170717155523.emckq2esjro6hf3z@suse.deReported-by: NNadav Amit <nadav.amit@gmail.com>
Signed-off-by: NMel Gorman <mgorman@suse.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: <stable@vger.kernel.org>	[v4.4+]
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      3ea27719
  3. 13 7月, 2017 1 次提交
    • M
      mm, tree wide: replace __GFP_REPEAT by __GFP_RETRY_MAYFAIL with more useful semantic · dcda9b04
      由 Michal Hocko 提交于 
      __GFP_REPEAT was designed to allow retry-but-eventually-fail semantic to
the page allocator.  This has been true but only for allocations
requests larger than PAGE_ALLOC_COSTLY_ORDER.  It has been always
ignored for smaller sizes.  This is a bit unfortunate because there is
no way to express the same semantic for those requests and they are
considered too important to fail so they might end up looping in the
page allocator for ever, similarly to GFP_NOFAIL requests.

Now that the whole tree has been cleaned up and accidental or misled
usage of __GFP_REPEAT flag has been removed for !costly requests we can
give the original flag a better name and more importantly a more useful
semantic.  Let's rename it to __GFP_RETRY_MAYFAIL which tells the user
that the allocator would try really hard but there is no promise of a
success.  This will work independent of the order and overrides the
default allocator behavior.  Page allocator users have several levels of
guarantee vs.  cost options (take GFP_KERNEL as an example)

 - GFP_KERNEL & ~__GFP_RECLAIM - optimistic allocation without _any_
   attempt to free memory at all. The most light weight mode which even
   doesn't kick the background reclaim. Should be used carefully because
   it might deplete the memory and the next user might hit the more
   aggressive reclaim

 - GFP_KERNEL & ~__GFP_DIRECT_RECLAIM (or GFP_NOWAIT)- optimistic
   allocation without any attempt to free memory from the current
   context but can wake kswapd to reclaim memory if the zone is below
   the low watermark. Can be used from either atomic contexts or when
   the request is a performance optimization and there is another
   fallback for a slow path.

 - (GFP_KERNEL|__GFP_HIGH) & ~__GFP_DIRECT_RECLAIM (aka GFP_ATOMIC) -
   non sleeping allocation with an expensive fallback so it can access
   some portion of memory reserves. Usually used from interrupt/bh
   context with an expensive slow path fallback.

 - GFP_KERNEL - both background and direct reclaim are allowed and the
   _default_ page allocator behavior is used. That means that !costly
   allocation requests are basically nofail but there is no guarantee of
   that behavior so failures have to be checked properly by callers
   (e.g. OOM killer victim is allowed to fail currently).

 - GFP_KERNEL | __GFP_NORETRY - overrides the default allocator behavior
   and all allocation requests fail early rather than cause disruptive
   reclaim (one round of reclaim in this implementation). The OOM killer
   is not invoked.

 - GFP_KERNEL | __GFP_RETRY_MAYFAIL - overrides the default allocator
   behavior and all allocation requests try really hard. The request
   will fail if the reclaim cannot make any progress. The OOM killer
   won't be triggered.

 - GFP_KERNEL | __GFP_NOFAIL - overrides the default allocator behavior
   and all allocation requests will loop endlessly until they succeed.
   This might be really dangerous especially for larger orders.

Existing users of __GFP_REPEAT are changed to __GFP_RETRY_MAYFAIL
because they already had their semantic.  No new users are added.
__alloc_pages_slowpath is changed to bail out for __GFP_RETRY_MAYFAIL if
there is no progress and we have already passed the OOM point.

This means that all the reclaim opportunities have been exhausted except
the most disruptive one (the OOM killer) and a user defined fallback
behavior is more sensible than keep retrying in the page allocator.

[akpm@linux-foundation.org: fix arch/sparc/kernel/mdesc.c]
[mhocko@suse.com: semantic fix]
  Link: http://lkml.kernel.org/r/20170626123847.GM11534@dhcp22.suse.cz
[mhocko@kernel.org: address other thing spotted by Vlastimil]
  Link: http://lkml.kernel.org/r/20170626124233.GN11534@dhcp22.suse.cz
Link: http://lkml.kernel.org/r/20170623085345.11304-3-mhocko@kernel.orgSigned-off-by: NMichal Hocko <mhocko@suse.com>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Cc: Alex Belits <alex.belits@cavium.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: David Daney <david.daney@cavium.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: NeilBrown <neilb@suse.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      dcda9b04
  5. 09 5月, 2017 3 次提交
    • V
      mm, compaction: finish whole pageblock to reduce fragmentation · baf6a9a1
      由 Vlastimil Babka 提交于 
      The main goal of direct compaction is to form a high-order page for
allocation, but it should also help against long-term fragmentation when
possible.

Most lower-than-pageblock-order compactions are for non-movable
allocations, which means that if we compact in a movable pageblock and
terminate as soon as we create the high-order page, it's unlikely that
the fallback heuristics will claim the whole block.  Instead there might
be a single unmovable page in a pageblock full of movable pages, and the
next unmovable allocation might pick another pageblock and increase
long-term fragmentation.

To help against such scenarios, this patch changes the termination
criteria for compaction so that the current pageblock is finished even
though the high-order page already exists.  Note that it might be
possible that the high-order page formed elsewhere in the zone due to
parallel activity, but this patch doesn't try to detect that.

This is only done with sync compaction, because async compaction is
limited to pageblock of the same migratetype, where it cannot result in
a migratetype fallback.  (Async compaction also eagerly skips
order-aligned blocks where isolation fails, which is against the goal of
migrating away as much of the pageblock as possible.)

As a result of this patch, long-term memory fragmentation should be
reduced.

In testing based on 4.9 kernel with stress-highalloc from mmtests
configured for order-4 GFP_KERNEL allocations, this patch has reduced
the number of unmovable allocations falling back to movable pageblocks
by 20%.  The number

Link: http://lkml.kernel.org/r/20170307131545.28577-9-vbabka@suse.czSigned-off-by: NVlastimil Babka <vbabka@suse.cz>
Acked-by: NMel Gorman <mgorman@techsingularity.net>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      baf6a9a1
    • V
      mm, compaction: add migratetype to compact_control · d39773a0
      由 Vlastimil Babka 提交于 
      Preparation patch.  We are going to need migratetype at lower layers
than compact_zone() and compact_finished().

Link: http://lkml.kernel.org/r/20170307131545.28577-7-vbabka@suse.czSigned-off-by: NVlastimil Babka <vbabka@suse.cz>
Acked-by: NMel Gorman <mgorman@techsingularity.net>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      d39773a0
    • V
      mm, compaction: reorder fields in struct compact_control · f25ba6dc
      由 Vlastimil Babka 提交于 
      Patch series "try to reduce fragmenting fallbacks", v3.

Last year, Johannes Weiner has reported a regression in page mobility
grouping [1] and while the exact cause was not found, I've come up with
some ways to improve it by reducing the number of allocations falling
back to different migratetype and causing permanent fragmentation.

The series was tested with mmtests stress-highalloc modified to do
GFP_KERNEL order-4 allocations, on 4.9 with "mm, vmscan: fix zone
balance check in prepare_kswapd_sleep" (without that, kcompactd indeed
wasn't woken up) on UMA machine with 4GB memory.  There were 5 repeats
of each run, as the extfrag stats are quite volatile (note the stats
below are sums, not averages, as it was less perl hacking for me).

Success rate are the same, already high due to the low allocation order
used, so I'm not including them.

Compaction stats:
(the patches are stacked, and I haven't measured the non-functional-changes
patches separately)

                                     patch 1     patch 2     patch 3     patch 4     patch 7     patch 8
  Compaction stalls                    22449       24680       24846       19765       22059       17480
  Compaction success                   12971       14836       14608       10475       11632        8757
  Compaction failures                   9477        9843       10238        9290       10426        8722
  Page migrate success               3109022     3370438     3312164     1695105     1608435     2111379
  Page migrate failure                911588     1149065     1028264     1112675     1077251     1026367
  Compaction pages isolated          7242983     8015530     7782467     4629063     4402787     5377665
  Compaction migrate scanned       980838938   987367943   957690188   917647238   947155598  1018922197
  Compaction free scanned          557926893   598946443   602236894   594024490   541169699   763651731
  Compaction cost                      10243       10578       10304        8286        8398        9440

Compaction stats are mostly within noise until patch 4, which decreases
the number of compactions, and migrations.  Part of that could be due to
more pageblocks marked as unmovable, and async compaction skipping
those.  This changes a bit with patch 7, but not so much.  Patch 8
increases free scanner stats and migrations, which comes from the
changed termination criteria.  Interestingly number of compactions
decreases - probably the fully compacted pageblock satisfies multiple
subsequent allocations, so it amortizes.

Next comes the extfrag tracepoint, where "fragmenting" means that an
allocation had to fallback to a pageblock of another migratetype which
wasn't fully free (which is almost all of the fallbacks).  I have
locally added another tracepoint for "Page steal" into
steal_suitable_fallback() which triggers in situations where we are
allowed to do move_freepages_block().  If we decide to also do
set_pageblock_migratetype(), it's "Pages steal with pageblock" with
break down for which allocation migratetype we are stealing and from
which fallback migratetype.  The last part "due to counting" comes from
patch 4 and counts the events where the counting of movable pages
allowed us to change pageblock's migratetype, while the number of free
pages alone wouldn't be enough to cross the threshold.

                                                       patch 1     patch 2     patch 3     patch 4     patch 7     patch 8
  Page alloc extfrag event                            10155066     8522968    10164959    15622080    13727068    13140319
  Extfrag fragmenting                                 10149231     8517025    10159040    15616925    13721391    13134792
  Extfrag fragmenting for unmovable                     159504      168500      184177       97835       70625       56948
  Extfrag fragmenting unmovable placed with movable     153613      163549      172693       91740       64099       50917
  Extfrag fragmenting unmovable placed with reclaim.      5891        4951       11484        6095        6526        6031
  Extfrag fragmenting for reclaimable                     4738        4829        6345        4822        5640        5378
  Extfrag fragmenting reclaimable placed with movable     1836        1902        1851        1579        1739        1760
  Extfrag fragmenting reclaimable placed with unmov.      2902        2927        4494        3243        3901        3618
  Extfrag fragmenting for movable                      9984989     8343696     9968518    15514268    13645126    13072466
  Pages steal                                           179954      192291      210880      123254       94545       81486
  Pages steal with pageblock                             22153       18943       20154       33562       29969       33444
  Pages steal with pageblock for unmovable               14350       12858       13256       20660       19003       20852
  Pages steal with pageblock for unmovable from mov.     12812       11402       11683       19072       17467       19298
  Pages steal with pageblock for unmovable from recl.     1538        1456        1573        1588        1536        1554
  Pages steal with pageblock for movable                  7114        5489        5965       11787       10012       11493
  Pages steal with pageblock for movable from unmov.      6885        5291        5541       11179        9525       10885
  Pages steal with pageblock for movable from recl.        229         198         424         608         487         608
  Pages steal with pageblock for reclaimable               689         596         933        1115         954        1099
  Pages steal with pageblock for reclaimable from unmov.   273         219         537         658         547         667
  Pages steal with pageblock for reclaimable from mov.     416         377         396         457         407         432
  Pages steal with pageblock due to counting                                                 11834       10075        7530
  ... for unmovable                                                                           8993        7381        4616
  ... for movable                                                                             2792        2653        2851
  ... for reclaimable                                                                           49          41          63

What we can see is that "Extfrag fragmenting for unmovable" and "...
placed with movable" drops with almost each patch, which is good as we
are polluting less movable pageblocks with unmovable pages.

The most significant change is patch 4 with movable page counting.  On
the other hand it increases "Extfrag fragmenting for movable" by 50%.
"Pages steal" drops though, so these movable allocation fallbacks find
only small free pages and are not allowed to steal whole pageblocks
back.  "Pages steal with pageblock" raises, because the patch increases
the chances of pageblock migratetype changes to happen.  This affects
all migratetypes.

The summary is that patch 4 is not a clear win wrt these stats, but I
believe that the tradeoff it makes is a good one.  There's less
pollution of movable pageblocks by unmovable allocations.  There's less
stealing between pageblock, and those that remain have higher chance of
changing migratetype also the pageblock itself, so it should more
faithfully reflect the migratetype of the pages within the pageblock.
The increase of movable allocations falling back to unmovable pageblock
might look dramatic, but those allocations can be migrated by compaction
when needed, and other patches in the series (7-9) improve that aspect.

Patches 7 and 8 continue the trend of reduced unmovable fallbacks and
also reduce the impact on movable fallbacks from patch 4.

[1] https://www.spinics.net/lists/linux-mm/msg114237.html

This patch (of 8):

While currently there are (mostly by accident) no holes in struct
compact_control (on x86_64), but we are going to add more bool flags, so
place them all together to the end of the structure.  While at it, just
order all fields from largest to smallest.

Link: http://lkml.kernel.org/r/20170307131545.28577-2-vbabka@suse.czSigned-off-by: NVlastimil Babka <vbabka@suse.cz>
Acked-by: NMel Gorman <mgorman@techsingularity.net>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      f25ba6dc
  7. 04 5月, 2017 3 次提交
    • X
      mm: use is_migrate_highatomic() to simplify the code · a6ffdc07
      由 Xishi Qiu 提交于 
      Introduce two helpers, is_migrate_highatomic() and is_migrate_highatomic_page().

Simplify the code, no functional changes.

[akpm@linux-foundation.org: use static inlines rather than macros, per mhocko]
Link: http://lkml.kernel.org/r/58B94F15.6060606@huawei.comSigned-off-by: NXishi Qiu <qiuxishi@huawei.com>
Acked-by: NMichal Hocko <mhocko@suse.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      a6ffdc07
    • J
      mm: delete NR_PAGES_SCANNED and pgdat_reclaimable() · c822f622
      由 Johannes Weiner 提交于 
      NR_PAGES_SCANNED counts number of pages scanned since the last page free
event in the allocator.  This was used primarily to measure the
reclaimability of zones and nodes, and determine when reclaim should
give up on them.  In that role, it has been replaced in the preceding
patches by a different mechanism.

Being implemented as an efficient vmstat counter, it was automatically
exported to userspace as well.  It's however unlikely that anyone
outside the kernel is using this counter in any meaningful way.

Remove the counter and the unused pgdat_reclaimable().

Link: http://lkml.kernel.org/r/20170228214007.5621-8-hannes@cmpxchg.orgSigned-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Acked-by: NHillf Danton <hillf.zj@alibaba-inc.com>
Acked-by: NMichal Hocko <mhocko@suse.com>
Cc: Jia He <hejianet@gmail.com>
Cc: Mel Gorman <mgorman@suse.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      c822f622
    • J
      mm: fix 100% CPU kswapd busyloop on unreclaimable nodes · c73322d0
      由 Johannes Weiner 提交于 
      Patch series "mm: kswapd spinning on unreclaimable nodes - fixes and
cleanups".

Jia reported a scenario in which the kswapd of a node indefinitely spins
at 100% CPU usage.  We have seen similar cases at Facebook.

The kernel's current method of judging its ability to reclaim a node (or
whether to back off and sleep) is based on the amount of scanned pages
in proportion to the amount of reclaimable pages.  In Jia's and our
scenarios, there are no reclaimable pages in the node, however, and the
condition for backing off is never met.  Kswapd busyloops in an attempt
to restore the watermarks while having nothing to work with.

This series reworks the definition of an unreclaimable node based not on
scanning but on whether kswapd is able to actually reclaim pages in
MAX_RECLAIM_RETRIES (16) consecutive runs.  This is the same criteria
the page allocator uses for giving up on direct reclaim and invoking the
OOM killer.  If it cannot free any pages, kswapd will go to sleep and
leave further attempts to direct reclaim invocations, which will either
make progress and re-enable kswapd, or invoke the OOM killer.

Patch #1 fixes the immediate problem Jia reported, the remainder are
smaller fixlets, cleanups, and overall phasing out of the old method.

Patch #6 is the odd one out.  It's a nice cleanup to get_scan_count(),
and directly related to #5, but in itself not relevant to the series.

If the whole series is too ambitious for 4.11, I would consider the
first three patches fixes, the rest cleanups.

This patch (of 9):

Jia He reports a problem with kswapd spinning at 100% CPU when
requesting more hugepages than memory available in the system:

$ echo 4000 >/proc/sys/vm/nr_hugepages

top - 13:42:59 up  3:37,  1 user,  load average: 1.09, 1.03, 1.01
Tasks:   1 total,   1 running,   0 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.0 us, 12.5 sy,  0.0 ni, 85.5 id,  2.0 wa,  0.0 hi,  0.0 si,  0.0 st
KiB Mem:  31371520 total, 30915136 used,   456384 free,      320 buffers
KiB Swap:  6284224 total,   115712 used,  6168512 free.    48192 cached Mem

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU  %MEM     TIME+ COMMAND
   76 root      20   0       0      0      0 R 100.0 0.000 217:17.29 kswapd3

At that time, there are no reclaimable pages left in the node, but as
kswapd fails to restore the high watermarks it refuses to go to sleep.

Kswapd needs to back away from nodes that fail to balance.  Up until
commit 1d82de61 ("mm, vmscan: make kswapd reclaim in terms of
nodes") kswapd had such a mechanism.  It considered zones whose
theoretically reclaimable pages it had reclaimed six times over as
unreclaimable and backed away from them.  This guard was erroneously
removed as the patch changed the definition of a balanced node.

However, simply restoring this code wouldn't help in the case reported
here: there *are* no reclaimable pages that could be scanned until the
threshold is met.  Kswapd would stay awake anyway.

Introduce a new and much simpler way of backing off.  If kswapd runs
through MAX_RECLAIM_RETRIES (16) cycles without reclaiming a single
page, make it back off from the node.  This is the same number of shots
direct reclaim takes before declaring OOM.  Kswapd will go to sleep on
that node until a direct reclaimer manages to reclaim some pages, thus
proving the node reclaimable again.

[hannes@cmpxchg.org: check kswapd failure against the cumulative nr_reclaimed count]
  Link: http://lkml.kernel.org/r/20170306162410.GB2090@cmpxchg.org
[shakeelb@google.com: fix condition for throttle_direct_reclaim]
  Link: http://lkml.kernel.org/r/20170314183228.20152-1-shakeelb@google.com
Link: http://lkml.kernel.org/r/20170228214007.5621-2-hannes@cmpxchg.orgSigned-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NShakeel Butt <shakeelb@google.com>
Reported-by: NJia He <hejianet@gmail.com>
Tested-by: NJia He <hejianet@gmail.com>
Acked-by: NMichal Hocko <mhocko@suse.com>
Acked-by: NHillf Danton <hillf.zj@alibaba-inc.com>
Acked-by: NMinchan Kim <minchan@kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      c73322d0
  9. 08 4月, 2017 1 次提交
  11. 25 2月, 2017 1 次提交
  13. 23 2月, 2017 3 次提交
  15. 26 12月, 2016 1 次提交
    • N
      mm: add PageWaiters indicating tasks are waiting for a page bit · 62906027
      由 Nicholas Piggin 提交于 
      Add a new page flag, PageWaiters, to indicate the page waitqueue has
tasks waiting. This can be tested rather than testing waitqueue_active
which requires another cacheline load.

This bit is always set when the page has tasks on page_waitqueue(page),
and is set and cleared under the waitqueue lock. It may be set when
there are no tasks on the waitqueue, which will cause a harmless extra
wakeup check that will clears the bit.

The generic bit-waitqueue infrastructure is no longer used for pages.
Instead, waitqueues are used directly with a custom key type. The
generic code was not flexible enough to have PageWaiters manipulation
under the waitqueue lock (which simplifies concurrency).

This improves the performance of page lock intensive microbenchmarks by
2-3%.

Putting two bits in the same word opens the opportunity to remove the
memory barrier between clearing the lock bit and testing the waiters
bit, after some work on the arch primitives (e.g., ensuring memory
operand widths match and cover both bits).
Signed-off-by: NNicholas Piggin <npiggin@gmail.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Bob Peterson <rpeterso@redhat.com>
Cc: Steven Whitehouse <swhiteho@redhat.com>
Cc: Andrew Lutomirski <luto@kernel.org>
Cc: Andreas Gruenbacher <agruenba@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      62906027
  17. 15 12月, 2016 2 次提交
  19. 08 10月, 2016 2 次提交
    • V
      mm, compaction: make full priority ignore pageblock suitability · 9f7e3387
      由 Vlastimil Babka 提交于 
      Several people have reported premature OOMs for order-2 allocations
(stack) due to OOM rework in 4.7.  In the scenario (parallel kernel
build and dd writing to two drives) many pageblocks get marked as
Unmovable and compaction free scanner struggles to isolate free pages.
Joonsoo Kim pointed out that the free scanner skips pageblocks that are
not movable to prevent filling them and forcing non-movable allocations
to fallback to other pageblocks.  Such heuristic makes sense to help
prevent long-term fragmentation, but premature OOMs are relatively more
urgent problem.  As a compromise, this patch disables the heuristic only
for the ultimate compaction priority.

Link: http://lkml.kernel.org/r/20160906135258.18335-5-vbabka@suse.czReported-by: NRalf-Peter Rohbeck <Ralf-Peter.Rohbeck@quantum.com>
Reported-by: NArkadiusz Miskiewicz <a.miskiewicz@gmail.com>
Reported-by: NOlaf Hering <olaf@aepfle.de>
Suggested-by: NJoonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: NVlastimil Babka <vbabka@suse.cz>
Acked-by: NMichal Hocko <mhocko@suse.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      9f7e3387
    • V
      mm, compaction: make whole_zone flag ignore cached scanner positions · 06ed2998
      由 Vlastimil Babka 提交于 
      Patch series "make direct compaction more deterministic")

This is mostly a followup to Michal's oom detection rework, which
highlighted the need for direct compaction to provide better feedback in
reclaim/compaction loop, so that it can reliably recognize when
compaction cannot make further progress, and allocation should invoke
OOM killer or fail.  We've discussed this at LSF/MM [1] where I proposed
expanding the async/sync migration mode used in compaction to more
general "priorities".  This patchset adds one new priority that just
overrides all the heuristics and makes compaction fully scan all zones.
I don't currently think that we need more fine-grained priorities, but
we'll see.  Other than that there's some smaller fixes and cleanups,
mainly related to the THP-specific hacks.

I've tested this with stress-highalloc in GFP_KERNEL order-4 and
THP-like order-9 scenarios.  There's some improvement for compaction
stats for the order-4, which is likely due to the better watermarks
handling.  In the previous version I reported mostly noise wrt
compaction stats, and decreased direct reclaim - now the reclaim is
without difference.  I believe this is due to the less aggressive
compaction priority increase in patch 6.

"before" is a mmotm tree prior to 4.7 release plus the first part of the
series that was sent and merged separately

                                    before        after
order-4:

Compaction stalls                    27216       30759
Compaction success                   19598       25475
Compaction failures                   7617        5283
Page migrate success                370510      464919
Page migrate failure                 25712       27987
Compaction pages isolated           849601     1041581
Compaction migrate scanned       143146541   101084990
Compaction free scanned          208355124   144863510
Compaction cost                       1403        1210

order-9:

Compaction stalls                     7311        7401
Compaction success                    1634        1683
Compaction failures                   5677        5718
Page migrate success                194657      183988
Page migrate failure                  4753        4170
Compaction pages isolated           498790      456130
Compaction migrate scanned          565371      524174
Compaction free scanned            4230296     4250744
Compaction cost                        215         203

[1] https://lwn.net/Articles/684611/

This patch (of 11):

A recent patch has added whole_zone flag that compaction sets when
scanning starts from the zone boundary, in order to report that zone has
been fully scanned in one attempt.  For allocations that want to try
really hard or cannot fail, we will want to introduce a mode where
scanning whole zone is guaranteed regardless of the cached positions.

This patch reuses the whole_zone flag in a way that if it's already
passed true to compaction, the cached scanner positions are ignored.
Employing this flag during reclaim/compaction loop will be done in the
next patch.  This patch however converts compaction invoked from
userspace via procfs to use this flag.  Before this patch, the cached
positions were first reset to zone boundaries and then read back from
struct zone, so there was a window where a parallel compaction could
replace the reset values, making the manual compaction less effective.
Using the flag instead of performing reset is more robust.

[akpm@linux-foundation.org: coding-style fixes]
Link: http://lkml.kernel.org/r/20160810091226.6709-2-vbabka@suse.czSigned-off-by: NVlastimil Babka <vbabka@suse.cz>
Tested-by: NLorenzo Stoakes <lstoakes@gmail.com>
Acked-by: NMichal Hocko <mhocko@suse.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      06ed2998
  21. 29 7月, 2016 4 次提交
    • V
      mm, compaction: simplify contended compaction handling · c3486f53
      由 Vlastimil Babka 提交于 
      Async compaction detects contention either due to failing trylock on
zone->lock or lru_lock, or by need_resched().  Since 1f9efdef ("mm,
compaction: khugepaged should not give up due to need_resched()") the
code got quite complicated to distinguish these two up to the
__alloc_pages_slowpath() level, so different decisions could be taken
for khugepaged allocations.

After the recent changes, khugepaged allocations don't check for
contended compaction anymore, so we again don't need to distinguish lock
and sched contention, and simplify the current convoluted code a lot.

However, I believe it's also possible to simplify even more and
completely remove the check for contended compaction after the initial
async compaction for costly orders, which was originally aimed at THP
page fault allocations.  There are several reasons why this can be done
now:

- with the new defaults, THP page faults no longer do reclaim/compaction at
  all, unless the system admin has overridden the default, or application has
  indicated via madvise that it can benefit from THP's. In both cases, it
  means that the potential extra latency is expected and worth the benefits.
- even if reclaim/compaction proceeds after this patch where it previously
  wouldn't, the second compaction attempt is still async and will detect the
  contention and back off, if the contention persists
- there are still heuristics like deferred compaction and pageblock skip bits
  in place that prevent excessive THP page fault latencies

Link: http://lkml.kernel.org/r/20160721073614.24395-9-vbabka@suse.czSigned-off-by: NVlastimil Babka <vbabka@suse.cz>
Acked-by: NMichal Hocko <mhocko@suse.com>
Acked-by: NMel Gorman <mgorman@techsingularity.net>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      c3486f53
    • M
      mm, page_alloc: remove fair zone allocation policy · e6cbd7f2
      由 Mel Gorman 提交于 
      The fair zone allocation policy interleaves allocation requests between
zones to avoid an age inversion problem whereby new pages are reclaimed
to balance a zone.  Reclaim is now node-based so this should no longer
be an issue and the fair zone allocation policy is not free.  This patch
removes it.

Link: http://lkml.kernel.org/r/1467970510-21195-30-git-send-email-mgorman@techsingularity.netSigned-off-by: NMel Gorman <mgorman@techsingularity.net>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@surriel.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      e6cbd7f2
    • M
      mm: convert zone_reclaim to node_reclaim · a5f5f91d
      由 Mel Gorman 提交于 
      As reclaim is now per-node based, convert zone_reclaim to be
node_reclaim.  It is possible that a node will be reclaimed multiple
times if it has multiple zones but this is unavoidable without caching
all nodes traversed so far.  The documentation and interface to
userspace is the same from a configuration perspective and will will be
similar in behaviour unless the node-local allocation requests were also
limited to lower zones.

Link: http://lkml.kernel.org/r/1467970510-21195-24-git-send-email-mgorman@techsingularity.netSigned-off-by: NMel Gorman <mgorman@techsingularity.net>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@surriel.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      a5f5f91d
    • M
      mm, vmscan: move LRU lists to node · 599d0c95
      由 Mel Gorman 提交于 
      This moves the LRU lists from the zone to the node and related data such
as counters, tracing, congestion tracking and writeback tracking.

Unfortunately, due to reclaim and compaction retry logic, it is
necessary to account for the number of LRU pages on both zone and node
logic.  Most reclaim logic is based on the node counters but the retry
logic uses the zone counters which do not distinguish inactive and
active sizes.  It would be possible to leave the LRU counters on a
per-zone basis but it's a heavier calculation across multiple cache
lines that is much more frequent than the retry checks.

Other than the LRU counters, this is mostly a mechanical patch but note
that it introduces a number of anomalies.  For example, the scans are
per-zone but using per-node counters.  We also mark a node as congested
when a zone is congested.  This causes weird problems that are fixed
later but is easier to review.

In the event that there is excessive overhead on 32-bit systems due to
the nodes being on LRU then there are two potential solutions

1. Long-term isolation of highmem pages when reclaim is lowmem

   When pages are skipped, they are immediately added back onto the LRU
   list. If lowmem reclaim persisted for long periods of time, the same
   highmem pages get continually scanned. The idea would be that lowmem
   keeps those pages on a separate list until a reclaim for highmem pages
   arrives that splices the highmem pages back onto the LRU. It potentially
   could be implemented similar to the UNEVICTABLE list.

   That would reduce the skip rate with the potential corner case is that
   highmem pages have to be scanned and reclaimed to free lowmem slab pages.

2. Linear scan lowmem pages if the initial LRU shrink fails

   This will break LRU ordering but may be preferable and faster during
   memory pressure than skipping LRU pages.

Link: http://lkml.kernel.org/r/1467970510-21195-4-git-send-email-mgorman@techsingularity.netSigned-off-by: NMel Gorman <mgorman@techsingularity.net>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Cc: Hillf Danton <hillf.zj@alibaba-inc.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@surriel.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      599d0c95
  23. 27 7月, 2016 3 次提交
  25. 25 6月, 2016 1 次提交
  27. 24 5月, 2016 2 次提交
    • M
      mm: make vm_mmap killable · 9fbeb5ab
      由 Michal Hocko 提交于 
      All the callers of vm_mmap seem to check for the failure already and
bail out in one way or another on the error which means that we can
change it to use killable version of vm_mmap_pgoff and return -EINTR if
the current task gets killed while waiting for mmap_sem.  This also
means that vm_mmap_pgoff can be killable by default and drop the
additional parameter.

This will help in the OOM conditions when the oom victim might be stuck
waiting for the mmap_sem for write which in turn can block oom_reaper
which relies on the mmap_sem for read to make a forward progress and
reclaim the address space of the victim.

Please note that load_elf_binary is ignoring vm_mmap error for
current->personality & MMAP_PAGE_ZERO case but that shouldn't be a
problem because the address is not used anywhere and we never return to
the userspace if we got killed.
Signed-off-by: NMichal Hocko <mhocko@suse.com>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      9fbeb5ab
    • M
      mm: make mmap_sem for write waits killable for mm syscalls · dc0ef0df
      由 Michal Hocko 提交于 
      This is a follow up work for oom_reaper [1].  As the async OOM killing
depends on oom_sem for read we would really appreciate if a holder for
write didn't stood in the way.  This patchset is changing many of
down_write calls to be killable to help those cases when the writer is
blocked and waiting for readers to release the lock and so help
__oom_reap_task to process the oom victim.

Most of the patches are really trivial because the lock is help from a
shallow syscall paths where we can return EINTR trivially and allow the
current task to die (note that EINTR will never get to the userspace as
the task has fatal signal pending).  Others seem to be easy as well as
the callers are already handling fatal errors and bail and return to
userspace which should be sufficient to handle the failure gracefully.
I am not familiar with all those code paths so a deeper review is really
appreciated.

As this work is touching more areas which are not directly connected I
have tried to keep the CC list as small as possible and people who I
believed would be familiar are CCed only to the specific patches (all
should have received the cover though).

This patchset is based on linux-next and it depends on
down_write_killable for rw_semaphores which got merged into tip
locking/rwsem branch and it is merged into this next tree.  I guess it
would be easiest to route these patches via mmotm because of the
dependency on the tip tree but if respective maintainers prefer other
way I have no objections.

I haven't covered all the mmap_write(mm->mmap_sem) instances here

  $ git grep "down_write(.*\<mmap_sem\>)" next/master | wc -l
  98
  $ git grep "down_write(.*\<mmap_sem\>)" | wc -l
  62

I have tried to cover those which should be relatively easy to review in
this series because this alone should be a nice improvement.  Other
places can be changed on top.

[0] http://lkml.kernel.org/r/1456752417-9626-1-git-send-email-mhocko@kernel.org
[1] http://lkml.kernel.org/r/1452094975-551-1-git-send-email-mhocko@kernel.org
[2] http://lkml.kernel.org/r/1456750705-7141-1-git-send-email-mhocko@kernel.org

This patch (of 18):

This is the first step in making mmap_sem write waiters killable.  It
focuses on the trivial ones which are taking the lock early after
entering the syscall and they are not changing state before.

Therefore it is very easy to change them to use down_write_killable and
immediately return with -EINTR.  This will allow the waiter to pass away
without blocking the mmap_sem which might be required to make a forward
progress.  E.g.  the oom reaper will need the lock for reading to
dismantle the OOM victim address space.

The only tricky function in this patch is vm_mmap_pgoff which has many
call sites via vm_mmap.  To reduce the risk keep vm_mmap with the
original non-killable semantic for now.

vm_munmap callers do not bother checking the return value so open code
it into the munmap syscall path for now for simplicity.
Signed-off-by: NMichal Hocko <mhocko@suse.com>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Cc: Mel Gorman <mgorman@suse.de>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      dc0ef0df
  29. 21 5月, 2016 1 次提交
    • M
      mm, compaction: distinguish between full and partial COMPACT_COMPLETE · c8f7de0b
      由 Michal Hocko 提交于 
      COMPACT_COMPLETE now means that compaction and free scanner met.  This
is not very useful information if somebody just wants to use this
feedback and make any decisions based on that.  The current caller might
be a poor guy who just happened to scan tiny portion of the zone and
that could be the reason no suitable pages were compacted.  Make sure we
distinguish the full and partial zone walks.

Consumers should treat COMPACT_PARTIAL_SKIPPED as a potential success
and be optimistic in retrying.

The existing users of COMPACT_COMPLETE are conservatively changed to use
COMPACT_PARTIAL_SKIPPED as well but some of them should be probably
reconsidered and only defer the compaction only for COMPACT_COMPLETE
with the new semantic.

This patch shouldn't introduce any functional changes.
Signed-off-by: NMichal Hocko <mhocko@suse.com>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Acked-by: NHillf Danton <hillf.zj@alibaba-inc.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <js1304@gmail.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      c8f7de0b
  31. 20 5月, 2016 4 次提交
  33. 26 3月, 2016 1 次提交
    • M
      mm, oom: introduce oom reaper · aac45363
      由 Michal Hocko 提交于 
      This patch (of 5):

This is based on the idea from Mel Gorman discussed during LSFMM 2015
and independently brought up by Oleg Nesterov.

The OOM killer currently allows to kill only a single task in a good
hope that the task will terminate in a reasonable time and frees up its
memory.  Such a task (oom victim) will get an access to memory reserves
via mark_oom_victim to allow a forward progress should there be a need
for additional memory during exit path.

It has been shown (e.g.  by Tetsuo Handa) that it is not that hard to
construct workloads which break the core assumption mentioned above and
the OOM victim might take unbounded amount of time to exit because it
might be blocked in the uninterruptible state waiting for an event (e.g.
lock) which is blocked by another task looping in the page allocator.

This patch reduces the probability of such a lockup by introducing a
specialized kernel thread (oom_reaper) which tries to reclaim additional
memory by preemptively reaping the anonymous or swapped out memory owned
by the oom victim under an assumption that such a memory won't be needed
when its owner is killed and kicked from the userspace anyway.  There is
one notable exception to this, though, if the OOM victim was in the
process of coredumping the result would be incomplete.  This is
considered a reasonable constrain because the overall system health is
more important than debugability of a particular application.

A kernel thread has been chosen because we need a reliable way of
invocation so workqueue context is not appropriate because all the
workers might be busy (e.g.  allocating memory).  Kswapd which sounds
like another good fit is not appropriate as well because it might get
blocked on locks during reclaim as well.

oom_reaper has to take mmap_sem on the target task for reading so the
solution is not 100% because the semaphore might be held or blocked for
write but the probability is reduced considerably wrt.  basically any
lock blocking forward progress as described above.  In order to prevent
from blocking on the lock without any forward progress we are using only
a trylock and retry 10 times with a short sleep in between.  Users of
mmap_sem which need it for write should be carefully reviewed to use
_killable waiting as much as possible and reduce allocations requests
done with the lock held to absolute minimum to reduce the risk even
further.

The API between oom killer and oom reaper is quite trivial.
wake_oom_reaper updates mm_to_reap with cmpxchg to guarantee only
NULL->mm transition and oom_reaper clear this atomically once it is done
with the work.  This means that only a single mm_struct can be reaped at
the time.  As the operation is potentially disruptive we are trying to
limit it to the ncessary minimum and the reaper blocks any updates while
it operates on an mm.  mm_struct is pinned by mm_count to allow parallel
exit_mmap and a race is detected by atomic_inc_not_zero(mm_users).
Signed-off-by: NMichal Hocko <mhocko@suse.com>
Suggested-by: NOleg Nesterov <oleg@redhat.com>
Suggested-by: NMel Gorman <mgorman@suse.de>
Acked-by: NMel Gorman <mgorman@suse.de>
Acked-by: NDavid Rientjes <rientjes@google.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Andrea Argangeli <andrea@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      aac45363
  35. 18 3月, 2016 4 次提交
    • J
      mm: convert printk(KERN_<LEVEL> to pr_<level> · 1170532b
      由 Joe Perches 提交于 
      Most of the mm subsystem uses pr_<level> so make it consistent.

Miscellanea:

 - Realign arguments
 - Add missing newline to format
 - kmemleak-test.c has a "kmemleak: " prefix added to the
   "Kmemleak testing" logging message via pr_fmt
Signed-off-by: NJoe Perches <joe@perches.com>
Acked-by: Tejun Heo <tj@kernel.org>	[percpu]
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      1170532b
    • J
      mm: introduce page reference manipulation functions · fe896d18
      由 Joonsoo Kim 提交于 
      The success of CMA allocation largely depends on the success of
migration and key factor of it is page reference count.  Until now, page
reference is manipulated by direct calling atomic functions so we cannot
follow up who and where manipulate it.  Then, it is hard to find actual
reason of CMA allocation failure.  CMA allocation should be guaranteed
to succeed so finding offending place is really important.

In this patch, call sites where page reference is manipulated are
converted to introduced wrapper function.  This is preparation step to
add tracepoint to each page reference manipulation function.  With this
facility, we can easily find reason of CMA allocation failure.  There is
no functional change in this patch.

In addition, this patch also converts reference read sites.  It will
help a second step that renames page._count to something else and
prevents later attempt to direct access to it (Suggested by Andrew).
Signed-off-by: NJoonsoo Kim <iamjoonsoo.kim@lge.com>
Acked-by: NMichal Nazarewicz <mina86@mina86.com>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      fe896d18
    • V
      mm, kswapd: replace kswapd compaction with waking up kcompactd · accf6242
      由 Vlastimil Babka 提交于 
      Similarly to direct reclaim/compaction, kswapd attempts to combine
reclaim and compaction to attempt making memory allocation of given
order available.

The details differ from direct reclaim e.g. in having high watermark as
a goal.  The code involved in kswapd's reclaim/compaction decisions has
evolved to be quite complex.

Testing reveals that it doesn't actually work in at least one scenario,
and closer inspection suggests that it could be greatly simplified
without compromising on the goal (make high-order page available) or
efficiency (don't reclaim too much).  The simplification relieas of
doing all compaction in kcompactd, which is simply woken up when high
watermarks are reached by kswapd's reclaim.

The scenario where kswapd compaction doesn't work was found with mmtests
test stress-highalloc configured to attempt order-9 allocations without
direct reclaim, just waking up kswapd.  There was no compaction attempt
from kswapd during the whole test.  Some added instrumentation shows
what happens:

 - balance_pgdat() sets end_zone to Normal, as it's not balanced
 - reclaim is attempted on DMA zone, which sets nr_attempted to 99, but
   it cannot reclaim anything, so sc.nr_reclaimed is 0
 - for zones DMA32 and Normal, kswapd_shrink_zone uses testorder=0, so
   it merely checks if high watermarks were reached for base pages.
   This is true, so no reclaim is attempted.  For DMA, testorder=0
   wasn't used, as compaction_suitable() returned COMPACT_SKIPPED
 - even though the pgdat_needs_compaction flag wasn't set to false, no
   compaction happens due to the condition sc.nr_reclaimed >
   nr_attempted being false (as 0 < 99)
 - priority-- due to nr_reclaimed being 0, repeat until priority reaches
   0 pgdat_balanced() is false as only the small zone DMA appears
   balanced (curiously in that check, watermark appears OK and
   compaction_suitable() returns COMPACT_PARTIAL, because a lower
   classzone_idx is used there)

Now, even if it was decided that reclaim shouldn't be attempted on the
DMA zone, the scenario would be the same, as (sc.nr_reclaimed=0 >
nr_attempted=0) is also false.  The condition really should use >= as
the comment suggests.  Then there is a mismatch in the check for setting
pgdat_needs_compaction to false using low watermark, while the rest uses
high watermark, and who knows what other subtlety.  Hopefully this
demonstrates that this is unsustainable.

Luckily we can simplify this a lot.  The reclaim/compaction decisions
make sense for direct reclaim scenario, but in kswapd, our primary goal
is to reach high watermark in order-0 pages.  Afterwards we can attempt
compaction just once.  Unlike direct reclaim, we don't reclaim extra
pages (over the high watermark), the current code already disallows it
for good reasons.

After this patch, we simply wake up kcompactd to process the pgdat,
after we have either succeeded or failed to reach the high watermarks in
kswapd, which goes to sleep.  We pass kswapd's order and classzone_idx,
so kcompactd can apply the same criteria to determine which zones are
worth compacting.  Note that we use the classzone_idx from
wakeup_kswapd(), not balanced_classzone_idx which can include higher
zones that kswapd tried to balance too, but didn't consider them in
pgdat_balanced().

Since kswapd now cannot create high-order pages itself, we need to
adjust how it determines the zones to be balanced.  The key element here
is adding a "highorder" parameter to zone_balanced, which, when set to
false, makes it consider only order-0 watermark instead of the desired
higher order (this was done previously by kswapd_shrink_zone(), but not
elsewhere).  This false is passed for example in pgdat_balanced().
Importantly, wakeup_kswapd() uses true to make sure kswapd and thus
kcompactd are woken up for a high-order allocation failure.

The last thing is to decide what to do with pageblock_skip bitmap
handling.  Compaction maintains a pageblock_skip bitmap to record
pageblocks where isolation recently failed.  This bitmap can be reset by
three ways:

1) direct compaction is restarting after going through the full deferred cycle

2) kswapd goes to sleep, and some other direct compaction has previously
   finished scanning the whole zone and set zone->compact_blockskip_flush.
   Note that a successful direct compaction clears this flag.

3) compaction was invoked manually via trigger in /proc

The case 2) is somewhat fuzzy to begin with, but after introducing
kcompactd we should update it.  The check for direct compaction in 1),
and to set the flush flag in 2) use current_is_kswapd(), which doesn't
work for kcompactd.  Thus, this patch adds bool direct_compaction to
compact_control to use in 2).  For the case 1) we remove the check
completely - unlike the former kswapd compaction, kcompactd does use the
deferred compaction functionality, so flushing tied to restarting from
deferred compaction makes sense here.

Note that when kswapd goes to sleep, kcompactd is woken up, so it will
see the flushed pageblock_skip bits.  This is different from when the
former kswapd compaction observed the bits and I believe it makes more
sense.  Kcompactd can afford to be more thorough than a direct
compaction trying to limit allocation latency, or kswapd whose primary
goal is to reclaim.

For testing, I used stress-highalloc configured to do order-9
allocations with GFP_NOWAIT|__GFP_HIGH|__GFP_COMP, so they relied just
on kswapd/kcompactd reclaim/compaction (the interfering kernel builds in
phases 1 and 2 work as usual):

stress-highalloc
                        4.5-rc1+before          4.5-rc1+after
                             -nodirect              -nodirect
Success 1 Min          1.00 (  0.00%)         5.00 (-66.67%)
Success 1 Mean         1.40 (  0.00%)         6.20 (-55.00%)
Success 1 Max          2.00 (  0.00%)         7.00 (-16.67%)
Success 2 Min          1.00 (  0.00%)         5.00 (-66.67%)
Success 2 Mean         1.80 (  0.00%)         6.40 (-52.38%)
Success 2 Max          3.00 (  0.00%)         7.00 (-16.67%)
Success 3 Min         34.00 (  0.00%)        62.00 (  1.59%)
Success 3 Mean        41.80 (  0.00%)        63.80 (  1.24%)
Success 3 Max         53.00 (  0.00%)        65.00 (  2.99%)

User                          3166.67        3181.09
System                        1153.37        1158.25
Elapsed                       1768.53        1799.37

                            4.5-rc1+before   4.5-rc1+after
                                 -nodirect    -nodirect
Direct pages scanned                32938        32797
Kswapd pages scanned              2183166      2202613
Kswapd pages reclaimed            2152359      2143524
Direct pages reclaimed              32735        32545
Percentage direct scans                1%           1%
THP fault alloc                       579          612
THP collapse alloc                    304          316
THP splits                              0            0
THP fault fallback                    793          778
THP collapse fail                      11           16
Compaction stalls                    1013         1007
Compaction success                     92           67
Compaction failures                   920          939
Page migrate success               238457       721374
Page migrate failure                23021        23469
Compaction pages isolated          504695      1479924
Compaction migrate scanned         661390      8812554
Compaction free scanned          13476658     84327916
Compaction cost                       262          838

After this patch we see improvements in allocation success rate
(especially for phase 3) along with increased compaction activity.  The
compaction stalls (direct compaction) in the interfering kernel builds
(probably THP's) also decreased somewhat thanks to kcompactd activity,
yet THP alloc successes improved a bit.

Note that elapsed and user time isn't so useful for this benchmark,
because of the background interference being unpredictable.  It's just
to quickly spot some major unexpected differences.  System time is
somewhat more useful and that didn't increase.

Also (after adjusting mmtests' ftrace monitor):

Time kswapd awake               2547781     2269241
Time kcompactd awake                  0      119253
Time direct compacting           939937      557649
Time kswapd compacting                0           0
Time kcompactd compacting             0      119099

The decrease of overal time spent compacting appears to not match the
increased compaction stats.  I suspect the tasks get rescheduled and
since the ftrace monitor doesn't see that, the reported time is wall
time, not CPU time.  But arguably direct compactors care about overall
latency anyway, whether busy compacting or waiting for CPU doesn't
matter.  And that latency seems to almost halved.

It's also interesting how much time kswapd spent awake just going
through all the priorities and failing to even try compacting, over and
over.

We can also configure stress-highalloc to perform both direct
reclaim/compaction and wakeup kswapd/kcompactd, by using
GFP_KERNEL|__GFP_HIGH|__GFP_COMP:

stress-highalloc
                        4.5-rc1+before         4.5-rc1+after
                               -direct               -direct
Success 1 Min          4.00 (  0.00%)        9.00 (-50.00%)
Success 1 Mean         8.00 (  0.00%)       10.00 (-19.05%)
Success 1 Max         12.00 (  0.00%)       11.00 ( 15.38%)
Success 2 Min          4.00 (  0.00%)        9.00 (-50.00%)
Success 2 Mean         8.20 (  0.00%)       10.00 (-16.28%)
Success 2 Max         13.00 (  0.00%)       11.00 (  8.33%)
Success 3 Min         75.00 (  0.00%)       74.00 (  1.33%)
Success 3 Mean        75.60 (  0.00%)       75.20 (  0.53%)
Success 3 Max         77.00 (  0.00%)       76.00 (  0.00%)

User                          3344.73       3246.04
System                        1194.24       1172.29
Elapsed                       1838.04       1836.76

                            4.5-rc1+before  4.5-rc1+after
                                   -direct     -direct
Direct pages scanned               125146      120966
Kswapd pages scanned              2119757     2135012
Kswapd pages reclaimed            2073183     2108388
Direct pages reclaimed             124909      120577
Percentage direct scans                5%          5%
THP fault alloc                       599         652
THP collapse alloc                    323         354
THP splits                              0           0
THP fault fallback                    806         793
THP collapse fail                      17          16
Compaction stalls                    2457        2025
Compaction success                    906         518
Compaction failures                  1551        1507
Page migrate success              2031423     2360608
Page migrate failure                32845       40852
Compaction pages isolated         4129761     4802025
Compaction migrate scanned       11996712    21750613
Compaction free scanned         214970969   344372001
Compaction cost                      2271        2694

In this scenario, this patch doesn't change the overall success rate as
direct compaction already tries all it can.  There's however significant
reduction in direct compaction stalls (that is, the number of
allocations that went into direct compaction).  The number of successes
(i.e.  direct compaction stalls that ended up with successful
allocation) is reduced by the same number.  This means the offload to
kcompactd is working as expected, and direct compaction is reduced
either due to detecting contention, or compaction deferred by kcompactd.
In the previous version of this patchset there was some apparent
reduction of success rate, but the changes in this version (such as
using sync compaction only), new baseline kernel, and/or averaging
results from 5 executions (my bet), made this go away.

Ftrace-based stats seem to roughly agree:

Time kswapd awake               2532984     2326824
Time kcompactd awake                  0      257916
Time direct compacting           864839      735130
Time kswapd compacting                0           0
Time kcompactd compacting             0      257585
Signed-off-by: NVlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: David Rientjes <rientjes@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      accf6242
    • N
      /proc/kpageflags: return KPF_BUDDY for "tail" buddy pages · 832fc1de
      由 Naoya Horiguchi 提交于 
      Currently /proc/kpageflags returns nothing for "tail" buddy pages, which
is inconvenient when grasping how free pages are distributed.  This
patch sets KPF_BUDDY for such pages.

With this patch:

  $ grep MemFree /proc/meminfo ; tools/vm/page-types -b buddy
  MemFree:         3134992 kB
               flags      page-count       MB  symbolic-flags                     long-symbolic-flags
  0x0000000000000400          779272     3044  __________B_______________________________ buddy
  0x0000000000000c00            4385       17  __________BM______________________________ buddy,mmap
               total          783657     3061

783657 pages is 3134628 kB (roughly consistent with the global counter,)
so it's OK.

[akpm@linux-foundation.org: update comment, per Naoya]
Signed-off-by: NNaoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Reviewed-by: NVladimir Davydov <vdavydov@virtuozzo.com&gt;>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      832fc1de
  37. 16 3月, 2016 2 次提交
    • J
      mm/compaction: speed up pageblock_pfn_to_page() when zone is contiguous · 7cf91a98
      由 Joonsoo Kim 提交于 
      There is a performance drop report due to hugepage allocation and in
there half of cpu time are spent on pageblock_pfn_to_page() in
compaction [1].

In that workload, compaction is triggered to make hugepage but most of
pageblocks are un-available for compaction due to pageblock type and
skip bit so compaction usually fails.  Most costly operations in this
case is to find valid pageblock while scanning whole zone range.  To
check if pageblock is valid to compact, valid pfn within pageblock is
required and we can obtain it by calling pageblock_pfn_to_page().  This
function checks whether pageblock is in a single zone and return valid
pfn if possible.  Problem is that we need to check it every time before
scanning pageblock even if we re-visit it and this turns out to be very
expensive in this workload.

Although we have no way to skip this pageblock check in the system where
hole exists at arbitrary position, we can use cached value for zone
continuity and just do pfn_to_page() in the system where hole doesn't
exist.  This optimization considerably speeds up in above workload.

Before vs After
  Max: 1096 MB/s vs 1325 MB/s
  Min: 635 MB/s 1015 MB/s
  Avg: 899 MB/s 1194 MB/s

Avg is improved by roughly 30% [2].

[1]: http://www.spinics.net/lists/linux-mm/msg97378.html
[2]: https://lkml.org/lkml/2015/12/9/23

[akpm@linux-foundation.org: don't forget to restore zone->contiguous on error path, per Vlastimil]
Signed-off-by: NJoonsoo Kim <iamjoonsoo.kim@lge.com>
Reported-by: NAaron Lu <aaron.lu@intel.com>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Tested-by: NAaron Lu <aaron.lu@intel.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Rik van Riel <riel@redhat.com>
Cc: David Rientjes <rientjes@google.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      7cf91a98
    • V
      mm, printk: introduce new format string for flags · edf14cdb
      由 Vlastimil Babka 提交于 
      In mm we use several kinds of flags bitfields that are sometimes printed
for debugging purposes, or exported to userspace via sysfs.  To make
them easier to interpret independently on kernel version and config, we
want to dump also the symbolic flag names.  So far this has been done
with repeated calls to pr_cont(), which is unreliable on SMP, and not
usable for e.g.  sysfs export.

To get a more reliable and universal solution, this patch extends
printk() format string for pointers to handle the page flags (%pGp),
gfp_flags (%pGg) and vma flags (%pGv).  Existing users of
dump_flag_names() are converted and simplified.

It would be possible to pass flags by value instead of pointer, but the
%p format string for pointers already has extensions for various kernel
structures, so it's a good fit, and the extra indirection in a
non-critical path is negligible.

[linux@rasmusvillemoes.dk: lots of good implementation suggestions]
Signed-off-by: NVlastimil Babka <vbabka@suse.cz>
Acked-by: NMichal Hocko <mhocko@suse.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Sasha Levin <sasha.levin@oracle.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Mel Gorman <mgorman@suse.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      edf14cdb