__swap_entry_free() always frees 1 entry.  Let's remove the usage.
Signed-off-by: NWei Yang <richard.weiyang@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NAndrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20200501015259.32237-2-richard.weiyang@gmail.comSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Now, the scalability of swap code will drop much when the swap device
becomes fragmented, because the swap slots allocation batching stops
working.  To solve the problem, in this patch, we will try to scan a
little more swap slots with restricted effort to batch the swap slots
allocation even if the swap device is fragmented.  Test shows that the
benchmark score can increase up to 37.1% with the patch.  Details are as
follows.

The swap code has a per-cpu cache of swap slots.  These batch swap space
allocations to improve swap subsystem scaling.  In the following code
path,

  add_to_swap()
    get_swap_page()
      refill_swap_slots_cache()
        get_swap_pages()
	  scan_swap_map_slots()

scan_swap_map_slots() and get_swap_pages() can return multiple swap
slots for each call.  These slots will be cached in the per-CPU swap
slots cache, so that several following swap slot requests will be
fulfilled there to avoid the lock contention in the lower level swap
space allocation/freeing code path.

But this only works when there are free swap clusters.  If a swap device
becomes so fragmented that there's no free swap clusters,
scan_swap_map_slots() and get_swap_pages() will return only one swap
slot for each call in the above code path.  Effectively, this falls back
to the situation before the swap slots cache was introduced, the heavy
lock contention on the swap related locks kills the scalability.

Why does it work in this way? Because the swap device could be large,
and the free swap slot scanning could be quite time consuming, to avoid
taking too much time to scanning free swap slots, the conservative
method was used.

In fact, this can be improved via scanning a little more free slots with
strictly restricted effort.  Which is implemented in this patch.  In
scan_swap_map_slots(), after the first free swap slot is gotten, we will
try to scan a little more, but only if we haven't scanned too many slots
(< LATENCY_LIMIT).  That is, the added scanning latency is strictly
restricted.

To test the patch, we have run 16-process pmbench memory benchmark on a
2-socket server machine with 48 cores.  Multiple ram disks are
configured as the swap devices.  The pmbench working-set size is much
larger than the available memory so that swapping is triggered.  The
memory read/write ratio is 80/20 and the accessing pattern is random, so
the swap space becomes highly fragmented during the test.  In the
original implementation, the lock contention on swap related locks is
very heavy.  The perf profiling data of the lock contention code path is
as following,

 _raw_spin_lock.get_swap_pages.get_swap_page.add_to_swap:             21.03
 _raw_spin_lock_irq.shrink_inactive_list.shrink_lruvec.shrink_node:    1.92
 _raw_spin_lock_irq.shrink_active_list.shrink_lruvec.shrink_node:      1.72
 _raw_spin_lock.free_pcppages_bulk.drain_pages_zone.drain_pages:       0.69

While after applying this patch, it becomes,

 _raw_spin_lock_irq.shrink_inactive_list.shrink_lruvec.shrink_node:    4.89
 _raw_spin_lock_irq.shrink_active_list.shrink_lruvec.shrink_node:      3.85
 _raw_spin_lock.free_pcppages_bulk.drain_pages_zone.drain_pages:       1.1
 _raw_spin_lock_irqsave.pagevec_lru_move_fn.__lru_cache_add.do_swap_page: 0.88

That is, the lock contention on the swap locks is eliminated.

And the pmbench score increases 37.1%.  The swapin throughput increases
45.7% from 2.02 GB/s to 2.94 GB/s.  While the swapout throughput increases
45.3% from 2.04 GB/s to 2.97 GB/s.
Signed-off-by: N"Huang, Ying" <ying.huang@intel.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Acked-by: NTim Chen <tim.c.chen@linux.intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Hugh Dickins <hughd@google.com>
Link: http://lkml.kernel.org/r/20200427030023.264780-1-ying.huang@intel.comSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

There are two duplicate code to handle the case when there is no available
swap entry.  To avoid this, we can compare tmp and max first and let the
second guard do its job.

No functional change is expected.
Signed-off-by: NWei Yang <richard.weiyang@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: N"Huang, Ying" <ying.huang@intel.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>
Link: http://lkml.kernel.org/r/20200421213824.8099-3-richard.weiyang@gmail.comSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

If tmp is bigger or equal to max, we would jump to new_cluster.

Return true directly.
Signed-off-by: NWei Yang <richard.weiyang@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: N"Huang, Ying" <ying.huang@intel.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>
Link: http://lkml.kernel.org/r/20200421213824.8099-2-richard.weiyang@gmail.comSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This is not necessary to use the variable found_free to record the status.
Just check tmp and max is enough.
Signed-off-by: NWei Yang <richard.weiyang@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: N"Huang, Ying" <ying.huang@intel.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Hugh Dickins <hughd@google.com>
Link: http://lkml.kernel.org/r/20200421213824.8099-1-richard.weiyang@gmail.comSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

scan_swap_map_slots() is only called by scan_swap_map() and
get_swap_pages().  Both ensure nr would not exceed SWAP_BATCH.

Just remove it.
Signed-off-by: NWei Yang <richard.weiyang@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Cc: Hugh Dickins <hughd@google.com>
Link: http://lkml.kernel.org/r/20200325220309.9803-2-richard.weiyang@gmail.comSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Use min3() to simplify the comparison and make it more self-explaining.
Signed-off-by: NWei Yang <richard.weiyang@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NAndrew Morton <akpm@linux-foundation.org>
Cc: Hugh Dickins <hughd@google.com>
Link: http://lkml.kernel.org/r/20200325220309.9803-1-richard.weiyang@gmail.comSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Now we can see there is redundant goto for SSD case.  In these two places,
we can just let the code walk through to the correct tag instead of
explicitly jump to it.

Let's remove them for better readability.
Signed-off-by: NWei Yang <richard.weiyang@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NAndrew Morton <akpm@linux-foundation.org>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Link: http://lkml.kernel.org/r/20200328060520.31449-4-richard.weiyang@gmail.comSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The code shows if this is ssd, it will jump to specific tag and skip the
following code for non-ssd.

Let's use "else if" to explicitly show the mutually exclusion for
ssd/non-ssd to reduce ambiguity.
Signed-off-by: NWei Yang <richard.weiyang@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NAndrew Morton <akpm@linux-foundation.org>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Link: http://lkml.kernel.org/r/20200328060520.31449-3-richard.weiyang@gmail.comSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

scan_swap_map_slots() is used to iterate swap_map[] array for an
available swap entry.  While after several optimizations, e.g.  for ssd
case, the logic of this function is a little not easy to catch.

This patchset tries to clean up the logic a little:

  * shows the ssd/non-ssd case is handled mutually exclusively
  * remove some unnecessary goto for ssd case

This patch (of 3):

When si->cluster_nr is zero, function would reach done and return.  The
increased offset would not be used any more.  This means we can move the
offset increment into the if clause.

This brings a further code cleanup possibility.
Signed-off-by: NWei Yang <richard.weiyang@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NAndrew Morton <akpm@linux-foundation.org>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Link: http://lkml.kernel.org/r/20200328060520.31449-1-richard.weiyang@gmail.com
Link: http://lkml.kernel.org/r/20200328060520.31449-2-richard.weiyang@gmail.comSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

In unuse_pte_range() we blindly swap-in pages without checking if the
swap entry is already present in the swap cache.

By doing this, the hit/miss ratio used by the swap readahead heuristic
is not properly updated and this leads to non-optimal performance during
swapoff.

Tracing the distribution of the readahead size returned by the swap
readahead heuristic during swapoff shows that a small readahead size is
used most of the time as if we had only misses (this happens both with
cluster and vma readahead), for example:

r::swapin_nr_pages(unsigned long offset):unsigned long:$retval
        COUNT      EVENT
        36948      $retval = 8
        44151      $retval = 4
        49290      $retval = 1
        527771     $retval = 2

Checking if the swap entry is present in the swap cache, instead, allows
to properly update the readahead statistics and the heuristic behaves in a
better way during swapoff, selecting a bigger readahead size:

r::swapin_nr_pages(unsigned long offset):unsigned long:$retval
        COUNT      EVENT
        1618       $retval = 1
        4960       $retval = 2
        41315      $retval = 4
        103521     $retval = 8

In terms of swapoff performance the result is the following:

Testing environment
===================

 - Host:
   CPU: 1.8GHz Intel Core i7-8565U (quad-core, 8MB cache)
   HDD: PC401 NVMe SK hynix 512GB
   MEM: 16GB

 - Guest (kvm):
   8GB of RAM
   virtio block driver
   16GB swap file on ext4 (/swapfile)

Test case
=========
 - allocate 85% of memory
 - `systemctl hibernate` to force all the pages to be swapped-out to the
   swap file
 - resume the system
 - measure the time that swapoff takes to complete:
   # /usr/bin/time swapoff /swapfile

Result (swapoff time)
======
                  5.6 vanilla   5.6 w/ this patch
                  -----------   -----------------
cluster-readahead      22.09s              12.19s
    vma-readahead      18.20s              15.33s

Conclusion
==========

The specific use case this patch is addressing is to improve swapoff
performance in cloud environments when a VM has been hibernated, resumed
and all the memory needs to be forced back to RAM by disabling swap.

This change allows to better exploits the advantages of the readahead
heuristic during swapoff and this improvement allows to to speed up the
resume process of such VMs.

[andrea.righi@canonical.com: update changelog]
  Link: http://lkml.kernel.org/r/20200418084705.GA147642@xps-13Signed-off-by: NAndrea Righi <andrea.righi@canonical.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: N"Huang, Ying" <ying.huang@intel.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Anchal Agarwal <anchalag@amazon.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Vineeth Remanan Pillai <vpillai@digitalocean.com>
Cc: Kelley Nielsen <kelleynnn@gmail.com>
Link: http://lkml.kernel.org/r/20200416180132.GB3352@xps-13Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

"prev_offset" is a static variable in swapin_nr_pages() that can be
accessed concurrently with only mmap_sem held in read mode as noticed by
KCSAN,

 BUG: KCSAN: data-race in swap_cluster_readahead / swap_cluster_readahead

 write to 0xffffffff92763830 of 8 bytes by task 14795 on cpu 17:
  swap_cluster_readahead+0x2a6/0x5e0
  swapin_readahead+0x92/0x8dc
  do_swap_page+0x49b/0xf20
  __handle_mm_fault+0xcfb/0xd70
  handle_mm_fault+0xfc/0x2f0
  do_page_fault+0x263/0x715
  page_fault+0x34/0x40

 1 lock held by (dnf)/14795:
  #0: ffff897bd2e98858 (&mm->mmap_sem#2){++++}-{3:3}, at: do_page_fault+0x143/0x715
  do_user_addr_fault at arch/x86/mm/fault.c:1405
  (inlined by) do_page_fault at arch/x86/mm/fault.c:1535
 irq event stamp: 83493
 count_memcg_event_mm+0x1a6/0x270
 count_memcg_event_mm+0x119/0x270
 __do_softirq+0x365/0x589
 irq_exit+0xa2/0xc0

 read to 0xffffffff92763830 of 8 bytes by task 1 on cpu 22:
  swap_cluster_readahead+0xfd/0x5e0
  swapin_readahead+0x92/0x8dc
  do_swap_page+0x49b/0xf20
  __handle_mm_fault+0xcfb/0xd70
  handle_mm_fault+0xfc/0x2f0
  do_page_fault+0x263/0x715
  page_fault+0x34/0x40

 1 lock held by systemd/1:
  #0: ffff897c38f14858 (&mm->mmap_sem#2){++++}-{3:3}, at: do_page_fault+0x143/0x715
 irq event stamp: 43530289
 count_memcg_event_mm+0x1a6/0x270
 count_memcg_event_mm+0x119/0x270
 __do_softirq+0x365/0x589
 irq_exit+0xa2/0xc0
Signed-off-by: NQian Cai <cai@lca.pw>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Cc: Marco Elver <elver@google.com>
Cc: Hugh Dickins <hughd@google.com>
Link: http://lkml.kernel.org/r/20200402213748.2237-1-cai@lca.pwSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Use list_{prev,next}_entry() instead of list_entry() for better
code readability.
Signed-off-by: Nchenqiwu <chenqiwu@xiaomi.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NAndrew Morton <akpm@linux-foundation.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Cc: Yang Shi <yang.shi@linux.alibaba.com>
Cc: Qian Cai <cai@lca.pw>
Cc: Baoquan He <bhe@redhat.com>
Link: http://lkml.kernel.org/r/1586599916-15456-2-git-send-email-qiwuchen55@gmail.comSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Describe the caller's responsibilities when passing
FAULT_FLAG_ALLOW_RETRY.

Link: http://lkml.kernel.org/r/1586915606.5647.5.camel@mtkswgap22Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Introduce pin_user_pages_unlocked(), which is nearly identical to the
get_user_pages_unlocked() that it wraps, except that it sets FOLL_PIN
and rejects FOLL_GET.
Signed-off-by: NJohn Hubbard <jhubbard@nvidia.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NAndrew Morton <akpm@linux-foundation.org>
Cc: Andy Walls <awalls@md.metrocast.net>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Link: http://lkml.kernel.org/r/20200518012157.1178336-2-jhubbard@nvidia.comSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This patch is an attempt to update the documentation.

 - Add/ remove extra * based on type of function static/global.

 - Add description for functions and their input arguments.

[akpm@linux-foundation.org: s@/*@/**@]
Signed-off-by: NSouptick Joarder <jrdr.linux@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NAndrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/1588013630-4497-1-git-send-email-jrdr.linux@gmail.comSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

After an NFS page has been written it is considered "unstable" until a
COMMIT request succeeds.  If the COMMIT fails, the page will be
re-written.

These "unstable" pages are currently accounted as "reclaimable", either
in WB_RECLAIMABLE, or in NR_UNSTABLE_NFS which is included in a
'reclaimable' count.  This might have made sense when sending the COMMIT
required a separate action by the VFS/MM (e.g.  releasepage() used to
send a COMMIT).  However now that all writes generated by ->writepages()
will automatically be followed by a COMMIT (since commit 919e3bd9
("NFS: Ensure we commit after writeback is complete")) it makes more
sense to treat them as writeback pages.

So this patch removes NR_UNSTABLE_NFS and accounts unstable pages in
NR_WRITEBACK and WB_WRITEBACK.

A particular effect of this change is that when
wb_check_background_flush() calls wb_over_bg_threshold(), the latter
will report 'true' a lot less often as the 'unstable' pages are no
longer considered 'dirty' (as there is nothing that writeback can do
about them anyway).

Currently wb_check_background_flush() will trigger writeback to NFS even
when there are relatively few dirty pages (if there are lots of unstable
pages), this can result in small writes going to the server (10s of
Kilobytes rather than a Megabyte) which hurts throughput.  With this
patch, there are fewer writes which are each larger on average.

Where the NR_UNSTABLE_NFS count was included in statistics
virtual-files, the entry is retained, but the value is hard-coded as
zero.  static trace points and warning printks which mentioned this
counter no longer report it.

[akpm@linux-foundation.org: re-layout comment]
[akpm@linux-foundation.org: fix printk warning]
Signed-off-by: NNeilBrown <neilb@suse.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NJan Kara <jack@suse.cz>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Acked-by: NTrond Myklebust <trond.myklebust@hammerspace.com>
Acked-by: Michal Hocko <mhocko@suse.com>	[mm]
Cc: Christoph Hellwig <hch@lst.de>
Cc: Chuck Lever <chuck.lever@oracle.com>
Link: http://lkml.kernel.org/r/87d06j7gqa.fsf@notabene.neil.brown.nameSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

PF_LESS_THROTTLE exists for loop-back nfsd (and a similar need in the
loop block driver and callers of prctl(PR_SET_IO_FLUSHER)), where a
daemon needs to write to one bdi (the final bdi) in order to free up
writes queued to another bdi (the client bdi).

The daemon sets PF_LESS_THROTTLE and gets a larger allowance of dirty
pages, so that it can still dirty pages after other processses have been
throttled.  The purpose of this is to avoid deadlock that happen when
the PF_LESS_THROTTLE process must write for any dirty pages to be freed,
but it is being thottled and cannot write.

This approach was designed when all threads were blocked equally,
independently on which device they were writing to, or how fast it was.
Since that time the writeback algorithm has changed substantially with
different threads getting different allowances based on non-trivial
heuristics.  This means the simple "add 25%" heuristic is no longer
reliable.

The important issue is not that the daemon needs a *larger* dirty page
allowance, but that it needs a *private* dirty page allowance, so that
dirty pages for the "client" bdi that it is helping to clear (the bdi
for an NFS filesystem or loop block device etc) do not affect the
throttling of the daemon writing to the "final" bdi.

This patch changes the heuristic so that the task is not throttled when
the bdi it is writing to has a dirty page count below below (or equal
to) the free-run threshold for that bdi.  This ensures it will always be
able to have some pages in flight, and so will not deadlock.

In a steady-state, it is expected that PF_LOCAL_THROTTLE tasks might
still be throttled by global threshold, but that is acceptable as it is
only the deadlock state that is interesting for this flag.

This approach of "only throttle when target bdi is busy" is consistent
with the other use of PF_LESS_THROTTLE in current_may_throttle(), were
it causes attention to be focussed only on the target bdi.

So this patch
 - renames PF_LESS_THROTTLE to PF_LOCAL_THROTTLE,
 - removes the 25% bonus that that flag gives, and
 - If PF_LOCAL_THROTTLE is set, don't delay at all unless the
   global and the local free-run thresholds are exceeded.

Note that previously realtime threads were treated the same as
PF_LESS_THROTTLE threads.  This patch does *not* change the behvaiour
for real-time threads, so it is now different from the behaviour of nfsd
and loop tasks.  I don't know what is wanted for realtime.

[akpm@linux-foundation.org: coding style fixes]
Signed-off-by: NNeilBrown <neilb@suse.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NJan Kara <jack@suse.cz>
Acked-by: Chuck Lever <chuck.lever@oracle.com>	[nfsd]
Cc: Christoph Hellwig <hch@lst.de>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Link: http://lkml.kernel.org/r/87ftbf7gs3.fsf@notabene.neil.brown.nameSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Commit 64081362 ("mm/page-writeback.c: fix range_cyclic writeback
vs writepages deadlock") left unused variable, remove it.
Signed-off-by: NChao Yu <yuchao0@huawei.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NDavid Hildenbrand <david@redhat.com>
Link: http://lkml.kernel.org/r/20200528033740.17269-1-yuchao0@huawei.comSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

We no longer return 0 here and the comment doesn't tell us anything that
we don't already know (SIGBUS is a pretty good indicator that things
didn't work out).
Signed-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NWilliam Kucharski <william.kucharski@oracle.com>
Link: http://lkml.kernel.org/r/20200529123243.20640-1-willy@infradead.orgSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

We can cleanup code a little by call detach_page_private here.

[akpm@linux-foundation.org: use attach_page_private(), per Dave]
  http://lkml.kernel.org/r/20200521225220.GV2005@dread.disaster.area
[akpm@linux-foundation.org: clear PagePrivate]
Signed-off-by: NGuoqing Jiang <guoqing.jiang@cloud.ionos.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NAndrew Morton <akpm@linux-foundation.org>
Cc: Chao Yu <yuchao0@huawei.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Gao Xiang <gaoxiang25@huawei.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Link: http://lkml.kernel.org/r/20200519214049.15179-1-guoqing.jiang@cloud.ionos.comSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Implement the new readahead aop and convert all callers (block_dev,
exfat, ext2, fat, gfs2, hpfs, isofs, jfs, nilfs2, ocfs2, omfs, qnx6,
reiserfs & udf).

The callers are all trivial except for GFS2 & OCFS2.
Signed-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: Junxiao Bi <junxiao.bi@oracle.com> # ocfs2
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com> # ocfs2
Reviewed-by: NDave Chinner <dchinner@redhat.com>
Reviewed-by: NJohn Hubbard <jhubbard@nvidia.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NWilliam Kucharski <william.kucharski@oracle.com>
Cc: Chao Yu <yuchao0@huawei.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Gao Xiang <gaoxiang25@huawei.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Link: http://lkml.kernel.org/r/20200414150233.24495-17-willy@infradead.orgSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Ensure that memory allocations in the readahead path do not attempt to
reclaim file-backed pages, which could lead to a deadlock.  It is
possible, though unlikely this is the root cause of a problem observed
by Cong Wang.
Reported-by: NCong Wang <xiyou.wangcong@gmail.com>
Suggested-by: NMichal Hocko <mhocko@suse.com>
Signed-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NWilliam Kucharski <william.kucharski@oracle.com>
Cc: Chao Yu <yuchao0@huawei.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Gao Xiang <gaoxiang25@huawei.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Link: http://lkml.kernel.org/r/20200414150233.24495-16-willy@infradead.orgSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

If the page is already in cache, we don't set PageReadahead on it.
Signed-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NWilliam Kucharski <william.kucharski@oracle.com>
Cc: Chao Yu <yuchao0@huawei.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Gao Xiang <gaoxiang25@huawei.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Link: http://lkml.kernel.org/r/20200414150233.24495-15-willy@infradead.orgSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

ext4 and f2fs have duplicated the guts of the readahead code so they can
read past i_size.  Instead, separate out the guts of the readahead code
so they can call it directly.
Signed-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Tested-by: NEric Biggers <ebiggers@google.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NWilliam Kucharski <william.kucharski@oracle.com>
Reviewed-by: NEric Biggers <ebiggers@google.com>
Cc: Chao Yu <yuchao0@huawei.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Gao Xiang <gaoxiang25@huawei.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Link: http://lkml.kernel.org/r/20200414150233.24495-14-willy@infradead.orgSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

By reducing nr_to_read, we can eliminate this check from inside the loop.
Signed-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NJohn Hubbard <jhubbard@nvidia.com>
Reviewed-by: NWilliam Kucharski <william.kucharski@oracle.com>
Cc: Chao Yu <yuchao0@huawei.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Gao Xiang <gaoxiang25@huawei.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Link: http://lkml.kernel.org/r/20200414150233.24495-13-willy@infradead.orgSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

This replaces ->readpages with a saner interface:
 - Return void instead of an ignored error code.
 - Page cache is already populated with locked pages when ->readahead
   is called.
 - New arguments can be passed to the implementation without changing
   all the filesystems that use a common helper function like
   mpage_readahead().
Signed-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NJohn Hubbard <jhubbard@nvidia.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NWilliam Kucharski <william.kucharski@oracle.com>
Cc: Chao Yu <yuchao0@huawei.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Gao Xiang <gaoxiang25@huawei.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Link: http://lkml.kernel.org/r/20200414150233.24495-12-willy@infradead.orgSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

When populating the page cache for readahead, mappings that use
->readpages must populate the page cache themselves as the pages are
passed on a linked list which would normally be used for the page
cache's LRU.  For mappings that use ->readpage or the upcoming
->readahead method, we can put the pages into the page cache as soon as
they're allocated, which solves a race between readahead and direct IO.
It also lets us remove the gfp argument from read_pages().

Use the new readahead_page() API to implement the repeated calls to
->readpage(), just like most filesystems will.
Signed-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NWilliam Kucharski <william.kucharski@oracle.com>
Cc: Chao Yu <yuchao0@huawei.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Gao Xiang <gaoxiang25@huawei.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Link: http://lkml.kernel.org/r/20200414150233.24495-11-willy@infradead.orgSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Replace the page_offset variable with 'index + i'.
Signed-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NJohn Hubbard <jhubbard@nvidia.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NWilliam Kucharski <william.kucharski@oracle.com>
Cc: Chao Yu <yuchao0@huawei.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Gao Xiang <gaoxiang25@huawei.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Link: http://lkml.kernel.org/r/20200414150233.24495-10-willy@infradead.orgSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Change the type of page_idx to unsigned long, and rename it -- it's just
a loop counter, not a page index.
Suggested-by: NJohn Hubbard <jhubbard@nvidia.com>
Signed-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NDave Chinner <dchinner@redhat.com>
Reviewed-by: NWilliam Kucharski <william.kucharski@oracle.com>
Reviewed-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: Chao Yu <yuchao0@huawei.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Gao Xiang <gaoxiang25@huawei.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Link: http://lkml.kernel.org/r/20200414150233.24495-9-willy@infradead.orgSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

The word 'offset' is used ambiguously to mean 'byte offset within a
page', 'byte offset from the start of the file' and 'page offset from
the start of the file'.

Use 'index' to mean 'page offset from the start of the file' throughout
the readahead code.

[ We should probably rename the 'pgoff_t' type to 'pgidx_t' too - Linus ]
Signed-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NZi Yan <ziy@nvidia.com>
Reviewed-by: NWilliam Kucharski <william.kucharski@oracle.com>
Cc: Chao Yu <yuchao0@huawei.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Gao Xiang <gaoxiang25@huawei.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Link: http://lkml.kernel.org/r/20200414150233.24495-8-willy@infradead.orgSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

In this patch, only between __do_page_cache_readahead() and
read_pages(), but it will be extended in upcoming patches.  The
read_pages() function becomes aops centric, as this makes the most sense
by the end of the patchset.
Signed-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NJohn Hubbard <jhubbard@nvidia.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NWilliam Kucharski <william.kucharski@oracle.com>
Reviewed-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: Chao Yu <yuchao0@huawei.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Gao Xiang <gaoxiang25@huawei.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Link: http://lkml.kernel.org/r/20200414150233.24495-7-willy@infradead.orgSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Simplify the callers by moving the check for nr_pages and the BUG_ON
into read_pages().
Signed-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NZi Yan <ziy@nvidia.com>
Reviewed-by: NJohn Hubbard <jhubbard@nvidia.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NWilliam Kucharski <william.kucharski@oracle.com>
Reviewed-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: Chao Yu <yuchao0@huawei.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Gao Xiang <gaoxiang25@huawei.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Link: http://lkml.kernel.org/r/20200414150233.24495-5-willy@infradead.orgSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

We used to assign the return value to a variable, which we then ignored.
Remove the pretence of caring.
Signed-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NDave Chinner <dchinner@redhat.com>
Reviewed-by: NJohn Hubbard <jhubbard@nvidia.com>
Reviewed-by: NWilliam Kucharski <william.kucharski@oracle.com>
Reviewed-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: Chao Yu <yuchao0@huawei.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Gao Xiang <gaoxiang25@huawei.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Link: http://lkml.kernel.org/r/20200414150233.24495-4-willy@infradead.orgSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

ondemand_readahead has two callers, neither of which use the return
value.  That means that both ra_submit and __do_page_cache_readahead()
can return void, and we don't need to worry that a present page in the
readahead window causes us to return a smaller nr_pages than we ought to
have.

Similarly, no caller uses the return value from
force_page_cache_readahead().
Signed-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NDave Chinner <dchinner@redhat.com>
Reviewed-by: NJohn Hubbard <jhubbard@nvidia.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NWilliam Kucharski <william.kucharski@oracle.com>
Cc: Chao Yu <yuchao0@huawei.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Gao Xiang <gaoxiang25@huawei.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Link: http://lkml.kernel.org/r/20200414150233.24495-3-willy@infradead.orgSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Patch series "Change readahead API", v11.

This series adds a readahead address_space operation to replace the
readpages operation.  The key difference is that pages are added to the
page cache as they are allocated (and then looked up by the filesystem)
instead of passing them on a list to the readpages operation and having
the filesystem add them to the page cache.  It's a net reduction in code
for each implementation, more efficient than walking a list, and solves
the direct-write vs buffered-read problem reported by yu kuai at
http://lkml.kernel.org/r/20200116063601.39201-1-yukuai3@huawei.com

The only unconverted filesystems are those which use fscache.  Their
conversion is pending Dave Howells' rewrite which will make the
conversion substantially easier.  This should be completed by the end of
the year.

I want to thank the reviewers/testers; Dave Chinner, John Hubbard, Eric
Biggers, Johannes Thumshirn, Dave Sterba, Zi Yan, Christoph Hellwig and
Miklos Szeredi have done a marvellous job of providing constructive
criticism.

These patches pass an xfstests run on ext4, xfs & btrfs with no
regressions that I can tell (some of the tests seem a little flaky
before and remain flaky afterwards).

This patch (of 25):

The readahead code is part of the page cache so should be found in the
pagemap.h file.  force_page_cache_readahead is only used within mm, so
move it to mm/internal.h instead.  Remove the parameter names where they
add no value, and rename the ones which were actively misleading.
Signed-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NJohn Hubbard <jhubbard@nvidia.com>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NWilliam Kucharski <william.kucharski@oracle.com>
Reviewed-by: NJohannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: Chao Yu <yuchao0@huawei.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Darrick J. Wong <darrick.wong@oracle.com>
Cc: Dave Chinner <dchinner@redhat.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Gao Xiang <gaoxiang25@huawei.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Link: http://lkml.kernel.org/r/20200414150233.24495-1-willy@infradead.org
Link: http://lkml.kernel.org/r/20200414150233.24495-2-willy@infradead.orgSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

We have seen a following problem on a RPi4 with 1G RAM:

    BUG: Bad page state in process systemd-hwdb  pfn:35601
    page:ffff7e0000d58040 refcount:15 mapcount:131221 mapping:efd8fe765bc80080 index:0x1 compound_mapcount: -32767
    Unable to handle kernel paging request at virtual address efd8fe765bc80080
    Mem abort info:
      ESR = 0x96000004
      Exception class = DABT (current EL), IL = 32 bits
      SET = 0, FnV = 0
      EA = 0, S1PTW = 0
    Data abort info:
      ISV = 0, ISS = 0x00000004
      CM = 0, WnR = 0
    [efd8fe765bc80080] address between user and kernel address ranges
    Internal error: Oops: 96000004 [#1] SMP
    Modules linked in: btrfs libcrc32c xor xor_neon zlib_deflate raid6_pq mmc_block xhci_pci xhci_hcd usbcore sdhci_iproc sdhci_pltfm sdhci mmc_core clk_raspberrypi gpio_raspberrypi_exp pcie_brcmstb bcm2835_dma gpio_regulator phy_generic fixed sg scsi_mod efivarfs
    Supported: No, Unreleased kernel
    CPU: 3 PID: 408 Comm: systemd-hwdb Not tainted 5.3.18-8-default #1 SLE15-SP2 (unreleased)
    Hardware name: raspberrypi rpi/rpi, BIOS 2020.01 02/21/2020
    pstate: 40000085 (nZcv daIf -PAN -UAO)
    pc : __dump_page+0x268/0x368
    lr : __dump_page+0xc4/0x368
    sp : ffff000012563860
    x29: ffff000012563860 x28: ffff80003ddc4300
    x27: 0000000000000010 x26: 000000000000003f
    x25: ffff7e0000d58040 x24: 000000000000000f
    x23: efd8fe765bc80080 x22: 0000000000020095
    x21: efd8fe765bc80080 x20: ffff000010ede8b0
    x19: ffff7e0000d58040 x18: ffffffffffffffff
    x17: 0000000000000001 x16: 0000000000000007
    x15: ffff000011689708 x14: 3030386362353637
    x13: 6566386466653a67 x12: 6e697070616d2031
    x11: 32323133313a746e x10: 756f6370616d2035
    x9 : ffff00001168a840 x8 : ffff00001077a670
    x7 : 000000000000013d x6 : ffff0000118a43b5
    x5 : 0000000000000001 x4 : ffff80003dd9e2c8
    x3 : ffff80003dd9e2c8 x2 : 911c8d7c2f483500
    x1 : dead000000000100 x0 : efd8fe765bc80080
    Call trace:
     __dump_page+0x268/0x368
     bad_page+0xd4/0x168
     check_new_page_bad+0x80/0xb8
     rmqueue_bulk.constprop.26+0x4d8/0x788
     get_page_from_freelist+0x4d4/0x1228
     __alloc_pages_nodemask+0x134/0xe48
     alloc_pages_vma+0x198/0x1c0
     do_anonymous_page+0x1a4/0x4d8
     __handle_mm_fault+0x4e8/0x560
     handle_mm_fault+0x104/0x1e0
     do_page_fault+0x1e8/0x4c0
     do_translation_fault+0xb0/0xc0
     do_mem_abort+0x50/0xb0
     el0_da+0x24/0x28
    Code: f9401025 8b8018a0 9a851005 17ffffca (f94002a0)

Besides the underlying issue with page->mapping containing a bogus value
for some reason, we can see that __dump_page() crashed by trying to read
the pointer at mapping->host, turning a recoverable warning into full
Oops.

It can be expected that when page is reported as bad state for some
reason, the pointers there should not be trusted blindly.

So this patch treats all data in __dump_page() that depends on
page->mapping as lava, using probe_kernel_read_strict().  Ideally this
would include the dentry->d_parent recursively, but that would mean
changing printk handler for %pd.  Chances of reaching the dentry
printing part with an initially bogus mapping pointer should be rather
low, though.

Also prefix printing mapping->a_ops with a description of what is being
printed.  In case the value is bogus, %ps will print raw value instead
of the symbol name and then it's not obvious at all that it's printing
a_ops.
Reported-by: NPetr Tesarik <ptesarik@suse.cz>
Signed-off-by: NVlastimil Babka <vbabka@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Acked-by: NKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Link: http://lkml.kernel.org/r/20200331165454.12263-1-vbabka@suse.czSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

There is no need to copy SLUB_STATS items from root memcg cache to new
memcg cache copies.  Doing so could result in stack overruns because the
store function only accepts 0 to clear the stat and returns an error for
everything else while the show method would print out the whole stat.

Then, the mismatch of the lengths returns from show and store methods
happens in memcg_propagate_slab_attrs():

	else if (root_cache->max_attr_size < ARRAY_SIZE(mbuf))
		buf = mbuf;

max_attr_size is only 2 from slab_attr_store(), then, it uses mbuf[64]
in show_stat() later where a bounch of sprintf() would overrun the stack
variable.  Fix it by always allocating a page of buffer to be used in
show_stat() if SLUB_STATS=y which should only be used for debug purpose.

  # echo 1 > /sys/kernel/slab/fs_cache/shrink
  BUG: KASAN: stack-out-of-bounds in number+0x421/0x6e0
  Write of size 1 at addr ffffc900256cfde0 by task kworker/76:0/53251

  Hardware name: HPE ProLiant DL385 Gen10/ProLiant DL385 Gen10, BIOS A40 07/10/2019
  Workqueue: memcg_kmem_cache memcg_kmem_cache_create_func
  Call Trace:
    number+0x421/0x6e0
    vsnprintf+0x451/0x8e0
    sprintf+0x9e/0xd0
    show_stat+0x124/0x1d0
    alloc_slowpath_show+0x13/0x20
    __kmem_cache_create+0x47a/0x6b0

  addr ffffc900256cfde0 is located in stack of task kworker/76:0/53251 at offset 0 in frame:
   process_one_work+0x0/0xb90

  this frame has 1 object:
   [32, 72) 'lockdep_map'

  Memory state around the buggy address:
   ffffc900256cfc80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
   ffffc900256cfd00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  >ffffc900256cfd80: 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1
                                                         ^
   ffffc900256cfe00: 00 00 00 00 00 f2 f2 f2 00 00 00 00 00 00 00 00
   ffffc900256cfe80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  ==================================================================
  Kernel panic - not syncing: stack-protector: Kernel stack is corrupted in: __kmem_cache_create+0x6ac/0x6b0
  Workqueue: memcg_kmem_cache memcg_kmem_cache_create_func
  Call Trace:
    __kmem_cache_create+0x6ac/0x6b0

Fixes: 107dab5c ("slub: slub-specific propagation changes")
Signed-off-by: NQian Cai <cai@lca.pw>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Cc: Glauber Costa <glauber@scylladb.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Link: http://lkml.kernel.org/r/20200429222356.4322-1-cai@lca.pwSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

list_slab_objects() is called when a slab is destroyed and there are
objects still left to list the objects in the syslog.  This is a pretty
rare event.

And there it seems we take the list_lock and call kmalloc while holding
that lock.

Perform the allocation in free_partial() before the list_lock is taken.

Fixes: bbd7d57b ("slub: Potential stack overflow")
Signed-off-by: NChristopher Lameter <cl@linux.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Cc: Yu Zhao <yuzhao@google.com>
Link: http://lkml.kernel.org/r/alpine.DEB.2.21.2002031721250.1668@www.lameter.comSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

I came across some unnecessary uevents once again which reminded me
this.  The patch seems to be lost in the leaves of the original
discussion [1], so resending.

[1] https://lore.kernel.org/r/alpine.DEB.2.21.2001281813130.745@www.lameter.com

Kmem caches are internal kernel structures so it is strange that
userspace notifiers would be needed.  And I am not aware of any use of
these notifiers.  These notifiers may just exist because in the initial
slub release the sysfs code was copied from another subsystem.
Signed-off-by: NChristoph Lameter <cl@linux.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Acked-by: NVlastimil Babka <vbabka@suse.cz>
Acked-by: NMichal Koutný <mkoutny@suse.com>
Acked-by: NDavid Rientjes <rientjes@google.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Link: http://lkml.kernel.org/r/20200423115721.19821-1-mkoutny@suse.comSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>