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  1. 24 4月, 2015 1 次提交
    • T
      writeback: use |1 instead of +1 to protect against div by zero · 464d1387
      由 Tejun Heo 提交于 
      mm/page-writeback.c has several places where 1 is added to the divisor
to prevent division by zero exceptions; however, if the original
divisor is equivalent to -1, adding 1 leads to division by zero.

There are three places where +1 is used for this purpose - one in
pos_ratio_polynom() and two in bdi_position_ratio().  The second one
in bdi_position_ratio() actually triggered div-by-zero oops on a
machine running a 3.10 kernel.  The divisor is

  x_intercept - bdi_setpoint + 1 == span + 1

span is confirmed to be (u32)-1.  It isn't clear how it ended up that
but it could be from write bandwidth calculation underflow fixed by
c72efb65 ("writeback: fix possible underflow in write bandwidth
calculation").

At any rate, +1 isn't a proper protection against div-by-zero.  This
patch converts all +1 protections to |1.  Note that
bdi_update_dirty_ratelimit() was already using |1 before this patch.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: stable@vger.kernel.org
Reviewed-by: NJan Kara <jack@suse.cz>
Signed-off-by: NJens Axboe <axboe@fb.com>
      464d1387
  3. 16 4月, 2015 1 次提交
  5. 15 4月, 2015 1 次提交
    • K
      page_writeback: clean up mess around cancel_dirty_page() · b9ea2515
      由 Konstantin Khlebnikov 提交于 
      This patch replaces cancel_dirty_page() with a helper function
account_page_cleaned() which only updates counters.  It's called from
truncate_complete_page() and from try_to_free_buffers() (hack for ext3).
Page is locked in both cases, page-lock protects against concurrent
dirtiers: see commit 2d6d7f98 ("mm: protect set_page_dirty() from
ongoing truncation").

Delete_from_page_cache() shouldn't be called for dirty pages, they must
be handled by caller (either written or truncated).  This patch treats
final dirty accounting fixup at the end of __delete_from_page_cache() as
a debug check and adds WARN_ON_ONCE() around it.  If something removes
dirty pages without proper handling that might be a bug and unwritten
data might be lost.

Hugetlbfs has no dirty pages accounting, ClearPageDirty() is enough
here.

cancel_dirty_page() in nfs_wb_page_cancel() is redundant.  This is
helper for nfs_invalidate_page() and it's called only in case complete
invalidation.

The mess was started in v2.6.20 after commits 46d2277c ("Clean up
and make try_to_free_buffers() not race with dirty pages") and
3e67c098 ("truncate: clear page dirtiness before running
try_to_free_buffers()") first was reverted right in v2.6.20 in commit
ecdfc978 ("Resurrect 'try_to_free_buffers()' VM hackery"), second in
v2.6.25 commit a2b34564 ("Fix dirty page accounting leak with ext3
data=journal").

Custom fixes were introduced between these points.  NFS in v2.6.23, commit
1b3b4a1a ("NFS: Fix a write request leak in nfs_invalidate_page()").
Kludge in __delete_from_page_cache() in v2.6.24, commit 3a692790 ("Do
dirty page accounting when removing a page from the page cache").  Since
v2.6.25 all of them are redundant.

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: NKonstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Tejun Heo <tj@kernel.org>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      b9ea2515
  7. 23 3月, 2015 1 次提交
    • T
      writeback: fix possible underflow in write bandwidth calculation · c72efb65
      由 Tejun Heo 提交于 
      From 1ebf33901ecc75d9496862dceb1ef0377980587c Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@kernel.org>
Date: Mon, 23 Mar 2015 00:08:19 -0400

2f800fbd ("writeback: fix dirtied pages accounting on redirty")
introduced account_page_redirty() which reverts stat updates for a
redirtied page, making BDI_DIRTIED no longer monotonically increasing.

bdi_update_write_bandwidth() uses the delta in BDI_DIRTIED as the
basis for bandwidth calculation.  While unlikely, since the above
patch, the newer value may be lower than the recorded past value and
underflow the bandwidth calculation leading to a wild result.

Fix it by subtracing min of the old and new values when calculating
delta.  AFAIK, there hasn't been any report of it happening but the
resulting erratic behavior would be non-critical and temporary, so
it's possible that the issue is happening without being reported.  The
risk of the fix is very low, so tagged for -stable.
Signed-off-by: NTejun Heo <tj@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jan Kara <jack@suse.cz>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Greg Thelen <gthelen@google.com>
Fixes: 2f800fbd ("writeback: fix dirtied pages accounting on redirty")
Cc: stable@vger.kernel.org
Signed-off-by: NJens Axboe <axboe@fb.com>
      c72efb65
  9. 04 3月, 2015 1 次提交
    • T
      writeback: add missing INITIAL_JIFFIES init in global_update_bandwidth() · 7d70e154
      由 Tejun Heo 提交于 
      global_update_bandwidth() uses static variable update_time as the
timestamp for the last update but forgets to initialize it to
INITIALIZE_JIFFIES.

This means that global_dirty_limit will be 5 mins into the future on
32bit and some large amount jiffies into the past on 64bit.  This
isn't critical as the only effect is that global_dirty_limit won't be
updated for the first 5 mins after booting on 32bit machines,
especially given the auxiliary nature of global_dirty_limit's role -
protecting against global dirty threshold's sudden dips; however, it
does lead to unintended suboptimal behavior.  Fix it.

Fixes: c42843f2 ("writeback: introduce smoothed global dirty limit")
Signed-off-by: NTejun Heo <tj@kernel.org>
Acked-by: NJan Kara <jack@suse.cz>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: stable@vger.kernel.org
Signed-off-by: NJens Axboe <axboe@fb.com>
      7d70e154
  11. 12 2月, 2015 2 次提交
  13. 21 1月, 2015 1 次提交
  15. 09 1月, 2015 1 次提交
    • J
      mm: protect set_page_dirty() from ongoing truncation · 2d6d7f98
      由 Johannes Weiner 提交于 
      Tejun, while reviewing the code, spotted the following race condition
between the dirtying and truncation of a page:

__set_page_dirty_nobuffers()       __delete_from_page_cache()
  if (TestSetPageDirty(page))
                                     page->mapping = NULL
				     if (PageDirty())
				       dec_zone_page_state(page, NR_FILE_DIRTY);
				       dec_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);
    if (page->mapping)
      account_page_dirtied(page)
        __inc_zone_page_state(page, NR_FILE_DIRTY);
	__inc_bdi_stat(mapping->backing_dev_info, BDI_RECLAIMABLE);

which results in an imbalance of NR_FILE_DIRTY and BDI_RECLAIMABLE.

Dirtiers usually lock out truncation, either by holding the page lock
directly, or in case of zap_pte_range(), by pinning the mapcount with
the page table lock held.  The notable exception to this rule, though,
is do_wp_page(), for which this race exists.  However, do_wp_page()
already waits for a locked page to unlock before setting the dirty bit,
in order to prevent a race where clear_page_dirty() misses the page bit
in the presence of dirty ptes.  Upgrade that wait to a fully locked
set_page_dirty() to also cover the situation explained above.

Afterwards, the code in set_page_dirty() dealing with a truncation race
is no longer needed.  Remove it.
Reported-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Acked-by: NKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: NJan Kara <jack@suse.cz>
Cc: <stable@vger.kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      2d6d7f98
  17. 11 12月, 2014 1 次提交
    • M
      mm, memcg: fix potential undefined behaviour in page stat accounting · e4bd6a02
      由 Michal Hocko 提交于 
      Since commit d7365e78 ("mm: memcontrol: fix missed end-writeback
page accounting") mem_cgroup_end_page_stat consumes locked and flags
variables directly rather than via pointers which might trigger C
undefined behavior as those variables are initialized only in the slow
path of mem_cgroup_begin_page_stat.

Although mem_cgroup_end_page_stat handles parameters correctly and
touches them only when they hold a sensible value it is caller which
loads a potentially uninitialized value which then might allow compiler
to do crazy things.

I haven't seen any warning from gcc and it seems that the current
version (4.9) doesn't exploit this type undefined behavior but Sasha has
reported the following:

  UBSan: Undefined behaviour in mm/rmap.c:1084:2
  load of value 255 is not a valid value for type '_Bool'
  CPU: 4 PID: 8304 Comm: rngd Not tainted 3.18.0-rc2-next-20141029-sasha-00039-g77ed13d-dirty #1427
  Call Trace:
    dump_stack (lib/dump_stack.c:52)
    ubsan_epilogue (lib/ubsan.c:159)
    __ubsan_handle_load_invalid_value (lib/ubsan.c:482)
    page_remove_rmap (mm/rmap.c:1084 mm/rmap.c:1096)
    unmap_page_range (./arch/x86/include/asm/atomic.h:27 include/linux/mm.h:463 mm/memory.c:1146 mm/memory.c:1258 mm/memory.c:1279 mm/memory.c:1303)
    unmap_single_vma (mm/memory.c:1348)
    unmap_vmas (mm/memory.c:1377 (discriminator 3))
    exit_mmap (mm/mmap.c:2837)
    mmput (kernel/fork.c:659)
    do_exit (./arch/x86/include/asm/thread_info.h:168 kernel/exit.c:462 kernel/exit.c:747)
    do_group_exit (include/linux/sched.h:775 kernel/exit.c:873)
    SyS_exit_group (kernel/exit.c:901)
    tracesys_phase2 (arch/x86/kernel/entry_64.S:529)

Fix this by using pointer parameters for both locked and flags and be
more robust for future compiler changes even though the current code is
implemented correctly.
Signed-off-by: NMichal Hocko <mhocko@suse.cz>
Reported-by: NSasha Levin <sasha.levin@oracle.com>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      e4bd6a02
  19. 30 10月, 2014 2 次提交
    • J
      mm: memcontrol: fix missed end-writeback page accounting · d7365e78
      由 Johannes Weiner 提交于 
      Commit 0a31bc97 ("mm: memcontrol: rewrite uncharge API") changed
page migration to uncharge the old page right away.  The page is locked,
unmapped, truncated, and off the LRU, but it could race with writeback
ending, which then doesn't unaccount the page properly:

test_clear_page_writeback()              migration
                                           wait_on_page_writeback()
  TestClearPageWriteback()
                                           mem_cgroup_migrate()
                                             clear PCG_USED
  mem_cgroup_update_page_stat()
    if (PageCgroupUsed(pc))
      decrease memcg pages under writeback

  release pc->mem_cgroup->move_lock

The per-page statistics interface is heavily optimized to avoid a
function call and a lookup_page_cgroup() in the file unmap fast path,
which means it doesn't verify whether a page is still charged before
clearing PageWriteback() and it has to do it in the stat update later.

Rework it so that it looks up the page's memcg once at the beginning of
the transaction and then uses it throughout.  The charge will be
verified before clearing PageWriteback() and migration can't uncharge
the page as long as that is still set.  The RCU lock will protect the
memcg past uncharge.

As far as losing the optimization goes, the following test results are
from a microbenchmark that maps, faults, and unmaps a 4GB sparse file
three times in a nested fashion, so that there are two negative passes
that don't account but still go through the new transaction overhead.
There is no actual difference:

 old:     33.195102545 seconds time elapsed       ( +-  0.01% )
 new:     33.199231369 seconds time elapsed       ( +-  0.03% )

The time spent in page_remove_rmap()'s callees still adds up to the
same, but the time spent in the function itself seems reduced:

     # Children      Self  Command        Shared Object       Symbol
 old:     0.12%     0.11%  filemapstress  [kernel.kallsyms]   [k] page_remove_rmap
 new:     0.12%     0.08%  filemapstress  [kernel.kallsyms]   [k] page_remove_rmap
Signed-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Cc: <stable@vger.kernel.org>	[3.17.x]
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      d7365e78
    • J
      mm: page-writeback: inline account_page_dirtied() into single caller · 3a3c02ec
      由 Johannes Weiner 提交于 
      A follow-up patch would have changed the call signature.  To save the
trouble, just fold it instead.
Signed-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Cc: <stable@vger.kernel.org>	[3.17.x]
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      3a3c02ec
  21. 10 10月, 2014 1 次提交
  23. 08 9月, 2014 1 次提交
  25. 07 8月, 2014 1 次提交
  27. 31 7月, 2014 1 次提交
  29. 07 6月, 2014 1 次提交
  31. 05 6月, 2014 2 次提交
  33. 12 5月, 2014 1 次提交
    • N
      ext4: fix data integrity sync in ordered mode · 1c8349a1
      由 Namjae Jeon 提交于 
      When we perform a data integrity sync we tag all the dirty pages with
PAGECACHE_TAG_TOWRITE at start of ext4_da_writepages.  Later we check
for this tag in write_cache_pages_da and creates a struct
mpage_da_data containing contiguously indexed pages tagged with this
tag and sync these pages with a call to mpage_da_map_and_submit.  This
process is done in while loop until all the PAGECACHE_TAG_TOWRITE
pages are synced. We also do journal start and stop in each iteration.
journal_stop could initiate journal commit which would call
ext4_writepage which in turn will call ext4_bio_write_page even for
delayed OR unwritten buffers. When ext4_bio_write_page is called for
such buffers, even though it does not sync them but it clears the
PAGECACHE_TAG_TOWRITE of the corresponding page and hence these pages
are also not synced by the currently running data integrity sync. We
will end up with dirty pages although sync is completed.

This could cause a potential data loss when the sync call is followed
by a truncate_pagecache call, which is exactly the case in
collapse_range.  (It will cause generic/127 failure in xfstests)

To avoid this issue, we can use set_page_writeback_keepwrite instead of
set_page_writeback, which doesn't clear TOWRITE tag.

Cc: stable@vger.kernel.org
Signed-off-by: NNamjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: NAshish Sangwan <a.sangwan@samsung.com>
Signed-off-by: N"Theodore Ts'o" <tytso@mit.edu>
Reviewed-by: NJan Kara <jack@suse.cz>
      1c8349a1
  35. 07 5月, 2014 1 次提交
  37. 08 4月, 2014 1 次提交
  39. 07 2月, 2014 1 次提交
    • K
      mm: __set_page_dirty_nobuffers() uses spin_lock_irqsave() instead of spin_lock_irq() · a85d9df1
      由 KOSAKI Motohiro 提交于 
      During aio stress test, we observed the following lockdep warning.  This
mean AIO+numa_balancing is currently deadlockable.

The problem is, aio_migratepage disable interrupt, but
__set_page_dirty_nobuffers unintentionally enable it again.

Generally, all helper function should use spin_lock_irqsave() instead of
spin_lock_irq() because they don't know caller at all.

   other info that might help us debug this:
    Possible unsafe locking scenario:

          CPU0
          ----
     lock(&(&ctx->completion_lock)->rlock);
     <Interrupt>
       lock(&(&ctx->completion_lock)->rlock);

    *** DEADLOCK ***

      dump_stack+0x19/0x1b
      print_usage_bug+0x1f7/0x208
      mark_lock+0x21d/0x2a0
      mark_held_locks+0xb9/0x140
      trace_hardirqs_on_caller+0x105/0x1d0
      trace_hardirqs_on+0xd/0x10
      _raw_spin_unlock_irq+0x2c/0x50
      __set_page_dirty_nobuffers+0x8c/0xf0
      migrate_page_copy+0x434/0x540
      aio_migratepage+0xb1/0x140
      move_to_new_page+0x7d/0x230
      migrate_pages+0x5e5/0x700
      migrate_misplaced_page+0xbc/0xf0
      do_numa_page+0x102/0x190
      handle_pte_fault+0x241/0x970
      handle_mm_fault+0x265/0x370
      __do_page_fault+0x172/0x5a0
      do_page_fault+0x1a/0x70
      page_fault+0x28/0x30
Signed-off-by: NKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Larry Woodman <lwoodman@redhat.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Johannes Weiner <jweiner@redhat.com>
Acked-by: NDavid Rientjes <rientjes@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      a85d9df1
  41. 30 1月, 2014 2 次提交
    • J
      mm/page-writeback.c: do not count anon pages as dirtyable memory · a1c3bfb2
      由 Johannes Weiner 提交于 
      The VM is currently heavily tuned to avoid swapping.  Whether that is
good or bad is a separate discussion, but as long as the VM won't swap
to make room for dirty cache, we can not consider anonymous pages when
calculating the amount of dirtyable memory, the baseline to which
dirty_background_ratio and dirty_ratio are applied.

A simple workload that occupies a significant size (40+%, depending on
memory layout, storage speeds etc.) of memory with anon/tmpfs pages and
uses the remainder for a streaming writer demonstrates this problem.  In
that case, the actual cache pages are a small fraction of what is
considered dirtyable overall, which results in an relatively large
portion of the cache pages to be dirtied.  As kswapd starts rotating
these, random tasks enter direct reclaim and stall on IO.

Only consider free pages and file pages dirtyable.
Signed-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Reported-by: NTejun Heo <tj@kernel.org>
Tested-by: NTejun Heo <tj@kernel.org>
Reviewed-by: NRik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Reviewed-by: NMichal Hocko <mhocko@suse.cz>
Cc: <stable@vger.kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      a1c3bfb2
    • J
      mm/page-writeback.c: fix dirty_balance_reserve subtraction from dirtyable memory · a804552b
      由 Johannes Weiner 提交于 
      Tejun reported stuttering and latency spikes on a system where random
tasks would enter direct reclaim and get stuck on dirty pages.  Around
50% of memory was occupied by tmpfs backed by an SSD, and another disk
(rotating) was reading and writing at max speed to shrink a partition.

: The problem was pretty ridiculous.  It's a 8gig machine w/ one ssd and 10k
: rpm harddrive and I could reliably reproduce constant stuttering every
: several seconds for as long as buffered IO was going on on the hard drive
: either with tmpfs occupying somewhere above 4gig or a test program which
: allocates about the same amount of anon memory.  Although swap usage was
: zero, turning off swap also made the problem go away too.
:
: The trigger conditions seem quite plausible - high anon memory usage w/
: heavy buffered IO and swap configured - and it's highly likely that this
: is happening in the wild too.  (this can happen with copying large files
: to usb sticks too, right?)

This patch (of 2):

The dirty_balance_reserve is an approximation of the fraction of free
pages that the page allocator does not make available for page cache
allocations.  As a result, it has to be taken into account when
calculating the amount of "dirtyable memory", the baseline to which
dirty_background_ratio and dirty_ratio are applied.

However, currently the reserve is subtracted from the sum of free and
reclaimable pages, which is non-sensical and leads to erroneous results
when the system is dominated by unreclaimable pages and the
dirty_balance_reserve is bigger than free+reclaimable.  In that case, at
least the already allocated cache should be considered dirtyable.

Fix the calculation by subtracting the reserve from the amount of free
pages, then adding the reclaimable pages on top.

[akpm@linux-foundation.org: fix CONFIG_HIGHMEM build]
Signed-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Reported-by: NTejun Heo <tj@kernel.org>
Tested-by: NTejun Heo <tj@kernel.org>
Reviewed-by: NRik van Riel <riel@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Reviewed-by: NMichal Hocko <mhocko@suse.cz>
Cc: <stable@vger.kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      a804552b
  43. 17 10月, 2013 1 次提交
    • F
      writeback: fix negative bdi max pause · e3b6c655
      由 Fengguang Wu 提交于 
      Toralf runs trinity on UML/i386.  After some time it hangs and the last
message line is

	BUG: soft lockup - CPU#0 stuck for 22s! [trinity-child0:1521]

It's found that pages_dirtied becomes very large.  More than 1000000000
pages in this case:

	period = HZ * pages_dirtied / task_ratelimit;
	BUG_ON(pages_dirtied > 2000000000);
	BUG_ON(pages_dirtied > 1000000000);      <---------

UML debug printf shows that we got negative pause here:

	ick: pause : -984
	ick: pages_dirtied : 0
	ick: task_ratelimit: 0

	 pause:
	+       if (pause < 0)  {
	+               extern int printf(char *, ...);
	+               printf("ick : pause : %li\n", pause);
	+               printf("ick: pages_dirtied : %lu\n", pages_dirtied);
	+               printf("ick: task_ratelimit: %lu\n", task_ratelimit);
	+               BUG_ON(1);
	+       }
	        trace_balance_dirty_pages(bdi,

Since pause is bounded by [min_pause, max_pause] where min_pause is also
bounded by max_pause.  It's suspected and demonstrated that the
max_pause calculation goes wrong:

	ick: pause : -717
	ick: min_pause : -177
	ick: max_pause : -717
	ick: pages_dirtied : 14
	ick: task_ratelimit: 0

The problem lies in the two "long = unsigned long" assignments in
bdi_max_pause() which might go negative if the highest bit is 1, and the
min_t(long, ...) check failed to protect it falling under 0.  Fix all of
them by using "unsigned long" throughout the function.
Signed-off-by: NFengguang Wu <fengguang.wu@intel.com>
Reported-by: NToralf Förster <toralf.foerster@gmx.de>
Tested-by: NToralf Förster <toralf.foerster@gmx.de>
Reviewed-by: NJan Kara <jack@suse.cz>
Cc: Richard Weinberger <richard@nod.at>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      e3b6c655
  45. 13 9月, 2013 1 次提交
    • S
      memcg: add per cgroup writeback pages accounting · 3ea67d06
      由 Sha Zhengju 提交于 
      Add memcg routines to count writeback pages, later dirty pages will also
be accounted.

After Kame's commit 89c06bd5 ("memcg: use new logic for page stat
accounting"), we can use 'struct page' flag to test page state instead
of per page_cgroup flag.  But memcg has a feature to move a page from a
cgroup to another one and may have race between "move" and "page stat
accounting".  So in order to avoid the race we have designed a new lock:

         mem_cgroup_begin_update_page_stat()
         modify page information        -->(a)
         mem_cgroup_update_page_stat()  -->(b)
         mem_cgroup_end_update_page_stat()

It requires both (a) and (b)(writeback pages accounting) to be pretected
in mem_cgroup_{begin/end}_update_page_stat().  It's full no-op for
!CONFIG_MEMCG, almost no-op if memcg is disabled (but compiled in), rcu
read lock in the most cases (no task is moving), and spin_lock_irqsave
on top in the slow path.

There're two writeback interfaces to modify: test_{clear/set}_page_writeback().
And the lock order is:
	--> memcg->move_lock
	  --> mapping->tree_lock
Signed-off-by: NSha Zhengju <handai.szj@taobao.com>
Acked-by: NMichal Hocko <mhocko@suse.cz>
Reviewed-by: NGreg Thelen <gthelen@google.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.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>
      3ea67d06
  47. 12 9月, 2013 3 次提交
    • M
      mm/page-writeback.c: add strictlimit feature · 5a537485
      由 Maxim Patlasov 提交于 
      The feature prevents mistrusted filesystems (ie: FUSE mounts created by
unprivileged users) to grow a large number of dirty pages before
throttling.  For such filesystems balance_dirty_pages always check bdi
counters against bdi limits.  I.e.  even if global "nr_dirty" is under
"freerun", it's not allowed to skip bdi checks.  The only use case for now
is fuse: it sets bdi max_ratio to 1% by default and system administrators
are supposed to expect that this limit won't be exceeded.

The feature is on if a BDI is marked by BDI_CAP_STRICTLIMIT flag.  A
filesystem may set the flag when it initializes its BDI.

The problematic scenario comes from the fact that nobody pays attention to
the NR_WRITEBACK_TEMP counter (i.e.  number of pages under fuse
writeback).  The implementation of fuse writeback releases original page
(by calling end_page_writeback) almost immediately.  A fuse request queued
for real processing bears a copy of original page.  Hence, if userspace
fuse daemon doesn't finalize write requests in timely manner, an
aggressive mmap writer can pollute virtually all memory by those temporary
fuse page copies.  They are carefully accounted in NR_WRITEBACK_TEMP, but
nobody cares.

To make further explanations shorter, let me use "NR_WRITEBACK_TEMP
problem" as a shortcut for "a possibility of uncontrolled grow of amount
of RAM consumed by temporary pages allocated by kernel fuse to process
writeback".

The problem was very easy to reproduce.  There is a trivial example
filesystem implementation in fuse userspace distribution: fusexmp_fh.c.  I
added "sleep(1);" to the write methods, then recompiled and mounted it.
Then created a huge file on the mount point and run a simple program which
mmap-ed the file to a memory region, then wrote a data to the region.  An
hour later I observed almost all RAM consumed by fuse writeback.  Since
then some unrelated changes in kernel fuse made it more difficult to
reproduce, but it is still possible now.

Putting this theoretical happens-in-the-lab thing aside, there is another
thing that really hurts real world (FUSE) users.  This is write-through
page cache policy FUSE currently uses.  I.e.  handling write(2), kernel
fuse populates page cache and flushes user data to the server
synchronously.  This is excessively suboptimal.  Pavel Emelyanov's patches
("writeback cache policy") solve the problem, but they also make resolving
NR_WRITEBACK_TEMP problem absolutely necessary.  Otherwise, simply copying
a huge file to a fuse mount would result in memory starvation.  Miklos,
the maintainer of FUSE, believes strictlimit feature the way to go.

And eventually putting FUSE topics aside, there is one more use-case for
strictlimit feature.  Using a slow USB stick (mass storage) in a machine
with huge amount of RAM installed is a well-known pain.  Let's make simple
computations.  Assuming 64GB of RAM installed, existing implementation of
balance_dirty_pages will start throttling only after 9.6GB of RAM becomes
dirty (freerun == 15% of total RAM).  So, the command "cp 9GB_file
/media/my-usb-storage/" may return in a few seconds, but subsequent
"umount /media/my-usb-storage/" will take more than two hours if effective
throughput of the storage is, to say, 1MB/sec.

After inclusion of strictlimit feature, it will be trivial to add a knob
(e.g.  /sys/devices/virtual/bdi/x:y/strictlimit) to enable it on demand.
Manually or via udev rule.  May be I'm wrong, but it seems to be quite a
natural desire to limit the amount of dirty memory for some devices we are
not fully trust (in the sense of sustainable throughput).

[akpm@linux-foundation.org: fix warning in page-writeback.c]
Signed-off-by: NMaxim Patlasov <MPatlasov@parallels.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Wu Fengguang <fengguang.wu@intel.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      5a537485
    • L
      mm: vmscan: fix do_try_to_free_pages() livelock · 6e543d57
      由 Lisa Du 提交于 
      This patch is based on KOSAKI's work and I add a little more description,
please refer https://lkml.org/lkml/2012/6/14/74.

Currently, I found system can enter a state that there are lots of free
pages in a zone but only order-0 and order-1 pages which means the zone is
heavily fragmented, then high order allocation could make direct reclaim
path's long stall(ex, 60 seconds) especially in no swap and no compaciton
enviroment.  This problem happened on v3.4, but it seems issue still lives
in current tree, the reason is do_try_to_free_pages enter live lock:

kswapd will go to sleep if the zones have been fully scanned and are still
not balanced.  As kswapd thinks there's little point trying all over again
to avoid infinite loop.  Instead it changes order from high-order to
0-order because kswapd think order-0 is the most important.  Look at
73ce02e9 in detail.  If watermarks are ok, kswapd will go back to sleep
and may leave zone->all_unreclaimable =3D 0.  It assume high-order users
can still perform direct reclaim if they wish.

Direct reclaim continue to reclaim for a high order which is not a
COSTLY_ORDER without oom-killer until kswapd turn on
zone->all_unreclaimble= .  This is because to avoid too early oom-kill.
So it means direct_reclaim depends on kswapd to break this loop.

In worst case, direct-reclaim may continue to page reclaim forever when
kswapd sleeps forever until someone like watchdog detect and finally kill
the process.  As described in:
http://thread.gmane.org/gmane.linux.kernel.mm/103737

We can't turn on zone->all_unreclaimable from direct reclaim path because
direct reclaim path don't take any lock and this way is racy.  Thus this
patch removes zone->all_unreclaimable field completely and recalculates
zone reclaimable state every time.

Note: we can't take the idea that direct-reclaim see zone->pages_scanned
directly and kswapd continue to use zone->all_unreclaimable.  Because, it
is racy.  commit 929bea7c (vmscan: all_unreclaimable() use
zone->all_unreclaimable as a name) describes the detail.

[akpm@linux-foundation.org: uninline zone_reclaimable_pages() and zone_reclaimable()]
Cc: Aaditya Kumar <aaditya.kumar.30@gmail.com>
Cc: Ying Han <yinghan@google.com>
Cc: Nick Piggin <npiggin@gmail.com>
Acked-by: NRik van Riel <riel@redhat.com>
Cc: Mel Gorman <mel@csn.ul.ie>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Bob Liu <lliubbo@gmail.com>
Cc: Neil Zhang <zhangwm@marvell.com>
Cc: Russell King - ARM Linux <linux@arm.linux.org.uk>
Reviewed-by: NMichal Hocko <mhocko@suse.cz>
Acked-by: NMinchan Kim <minchan@kernel.org>
Acked-by: NJohannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: NLisa Du <cldu@marvell.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      6e543d57
    • J
      mm: revert "page-writeback.c: subtract min_free_kbytes from dirtyable memory" · 72457c0a
      由 Johannes Weiner 提交于 
      This reverts commit 75f7ad8e.  It was the result of a problem
observed with a 3.2 kernel and merged in 3.9, while the issue had been
resolved upstream in 3.3 (commit ab8fabd4: "mm: exclude reserved
pages from dirtyable memory").

The "reserved pages" are a superset of min_free_kbytes, thus this change
is redundant and confusing.  Revert it.
Signed-off-by: NJohannes Weiner <hannes@cmpxchg.org>
Cc: Paul Szabo <psz@maths.usyd.edu.au>
Cc: Rik van Riel <riel@redhat.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>
      72457c0a
  49. 15 7月, 2013 1 次提交
    • P
      kernel: delete __cpuinit usage from all core kernel files · 0db0628d
      由 Paul Gortmaker 提交于 
      The __cpuinit type of throwaway sections might have made sense
some time ago when RAM was more constrained, but now the savings
do not offset the cost and complications.  For example, the fix in
commit 5e427ec2 ("x86: Fix bit corruption at CPU resume time")
is a good example of the nasty type of bugs that can be created
with improper use of the various __init prefixes.

After a discussion on LKML[1] it was decided that cpuinit should go
the way of devinit and be phased out.  Once all the users are gone,
we can then finally remove the macros themselves from linux/init.h.

This removes all the uses of the __cpuinit macros from C files in
the core kernel directories (kernel, init, lib, mm, and include)
that don't really have a specific maintainer.

[1] https://lkml.org/lkml/2013/5/20/589Signed-off-by: NPaul Gortmaker <paul.gortmaker@windriver.com>
      0db0628d
  51. 30 4月, 2013 1 次提交
    • D
      mm: make snapshotting pages for stable writes a per-bio operation · 71368511
      由 Darrick J. Wong 提交于 
      Walking a bio's page mappings has proved problematic, so create a new
bio flag to indicate that a bio's data needs to be snapshotted in order
to guarantee stable pages during writeback.  Next, for the one user
(ext3/jbd) of snapshotting, hook all the places where writes can be
initiated without PG_writeback set, and set BIO_SNAP_STABLE there.

We must also flag journal "metadata" bios for stable writeout, since
file data can be written through the journal.  Finally, the
MS_SNAP_STABLE mount flag (only used by ext3) is now superfluous, so get
rid of it.

[akpm@linux-foundation.org: rename _submit_bh()'s `flags' to `bio_flags', delobotomize the _submit_bh declaration]
[akpm@linux-foundation.org: teeny cleanup]
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Artem Bityutskiy <dedekind1@gmail.com>
Reviewed-by: NJan Kara <jack@suse.cz>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      71368511
  53. 24 2月, 2013 1 次提交
  55. 22 2月, 2013 2 次提交
    • D
      block: optionally snapshot page contents to provide stable pages during write · ffecfd1a
      由 Darrick J. Wong 提交于 
      This provides a band-aid to provide stable page writes on jbd without
needing to backport the fixed locking and page writeback bit handling
schemes of jbd2.  The band-aid works by using bounce buffers to snapshot
page contents instead of waiting.

For those wondering about the ext3 bandage -- fixing the jbd locking
(which was done as part of ext4dev years ago) is a lot of surgery, and
setting PG_writeback on data pages when we actually hold the page lock
dropped ext3 performance by nearly an order of magnitude.  If we're
going to migrate iscsi and raid to use stable page writes, the
complaints about high latency will likely return.  We might as well
centralize their page snapshotting thing to one place.
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>
Tested-by: NAndy Lutomirski <luto@amacapital.net>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Artem Bityutskiy <dedekind1@gmail.com>
Reviewed-by: NJan Kara <jack@suse.cz>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Mark Fasheh <mfasheh@suse.com>
Cc: Steven Whitehouse <swhiteho@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Eric Van Hensbergen <ericvh@gmail.com>
Cc: Ron Minnich <rminnich@sandia.gov>
Cc: Latchesar Ionkov <lucho@ionkov.net>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      ffecfd1a
    • D
      mm: only enforce stable page writes if the backing device requires it · 1d1d1a76
      由 Darrick J. Wong 提交于 
      Create a helper function to check if a backing device requires stable
page writes and, if so, performs the necessary wait.  Then, make it so
that all points in the memory manager that handle making pages writable
use the helper function.  This should provide stable page write support
to most filesystems, while eliminating unnecessary waiting for devices
that don't require the feature.

Before this patchset, all filesystems would block, regardless of whether
or not it was necessary.  ext3 would wait, but still generate occasional
checksum errors.  The network filesystems were left to do their own
thing, so they'd wait too.

After this patchset, all the disk filesystems except ext3 and btrfs will
wait only if the hardware requires it.  ext3 (if necessary) snapshots
pages instead of blocking, and btrfs provides its own bdi so the mm will
never wait.  Network filesystems haven't been touched, so either they
provide their own stable page guarantees or they don't block at all.
The blocking behavior is back to what it was before 3.0 if you don't
have a disk requiring stable page writes.

Here's the result of using dbench to test latency on ext2:

3.8.0-rc3:
 Operation      Count    AvgLat    MaxLat
 ----------------------------------------
 WriteX        109347     0.028    59.817
 ReadX         347180     0.004     3.391
 Flush          15514    29.828   287.283

Throughput 57.429 MB/sec  4 clients  4 procs  max_latency=287.290 ms

3.8.0-rc3 + patches:
 WriteX        105556     0.029     4.273
 ReadX         335004     0.005     4.112
 Flush          14982    30.540   298.634

Throughput 55.4496 MB/sec  4 clients  4 procs  max_latency=298.650 ms

As you can see, the maximum write latency drops considerably with this
patch enabled.  The other filesystems (ext3/ext4/xfs/btrfs) behave
similarly, but see the cover letter for those results.
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>
Acked-by: NSteven Whitehouse <swhiteho@redhat.com>
Reviewed-by: NJan Kara <jack@suse.cz>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Artem Bityutskiy <dedekind1@gmail.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Mark Fasheh <mfasheh@suse.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Eric Van Hensbergen <ericvh@gmail.com>
Cc: Ron Minnich <rminnich@sandia.gov>
Cc: Latchesar Ionkov <lucho@ionkov.net>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
      1d1d1a76
  57. 08 2月, 2013 1 次提交
  59. 24 1月, 2013 1 次提交
  61. 14 1月, 2013 1 次提交
    • T
      writeback: add more tracepoints · 9fb0a7da
      由 Tejun Heo 提交于 
      Add tracepoints for page dirtying, writeback_single_inode start, inode
dirtying and writeback.  For the latter two inode events, a pair of
events are defined to denote start and end of the operations (the
starting one has _start suffix and the one w/o suffix happens after
the operation is complete).  These inode ops are FS specific and can
be non-trivial and having enclosing tracepoints is useful for external
tracers.

This is part of tracepoint additions to improve visiblity into
dirtying / writeback operations for io tracer and userland.

v2: writeback_dirty_inode[_start] TPs may be called for files on
    pseudo FSes w/ unregistered bdi.  Check whether bdi->dev is %NULL
    before dereferencing.

v3: buffer dirtying moved to a block TP.
Signed-off-by: NTejun Heo <tj@kernel.org>
Reviewed-by: NJan Kara <jack@suse.cz>
Signed-off-by: NJens Axboe <axboe@kernel.dk>
      9fb0a7da
  63. 21 12月, 2012 1 次提交
  65. 12 12月, 2012 1 次提交