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| author | Tejun Heo <tj@kernel.org> | 2016-05-27 14:34:46 -0400 |
|---|---|---|
| committer | Jens Axboe <axboe@fb.com> | 2016-05-30 08:54:40 -0600 |
| commit | 62a584fe05eef1f80ed49a286a29328f1a224fb9 (patch) | |
| tree | cf34bae00e267a9e5fb94a70d7f24f893d325e6b /mm/page-writeback.c | |
| parent | b02b1fbdd338f70e49efa9ca9899214134526701 (diff) | |
| download | lwn-62a584fe05eef1f80ed49a286a29328f1a224fb9.tar.gz lwn-62a584fe05eef1f80ed49a286a29328f1a224fb9.zip | |
writeback: use higher precision calculation in domain_dirty_limits()
As vm.dirty_[background_]bytes can't be applied verbatim to multiple
cgroup writeback domains, they get converted to percentages in
domain_dirty_limits() and applied the same way as
vm.dirty_[background]ratio. However, if the specified bytes is lower
than 1% of available memory, the calculated ratios become zero and the
writeback domain gets throttled constantly.
Fix it by using per-PAGE_SIZE instead of percentage for ratio
calculations. Also, the updated DIV_ROUND_UP() usages now should
yield 1/4096 (0.0244%) as the minimum ratio as long as the specified
bytes are above zero.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Miao Xie <miaoxie@huawei.com>
Link: http://lkml.kernel.org/g/57333E75.3080309@huawei.com
Cc: stable@vger.kernel.org # v4.2+
Fixes: 9fc3a43e1757 ("writeback: separate out domain_dirty_limits()")
Reviewed-by: Jan Kara <jack@suse.cz>
Adjusted comment based on Jan's suggestion.
Signed-off-by: Jens Axboe <axboe@fb.com>
Diffstat (limited to 'mm/page-writeback.c')
| -rw-r--r-- | mm/page-writeback.c | 21 |
1 files changed, 12 insertions, 9 deletions
diff --git a/mm/page-writeback.c b/mm/page-writeback.c index b9956fdee8f5..e2481949494c 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -373,8 +373,9 @@ static void domain_dirty_limits(struct dirty_throttle_control *dtc) struct dirty_throttle_control *gdtc = mdtc_gdtc(dtc); unsigned long bytes = vm_dirty_bytes; unsigned long bg_bytes = dirty_background_bytes; - unsigned long ratio = vm_dirty_ratio; - unsigned long bg_ratio = dirty_background_ratio; + /* convert ratios to per-PAGE_SIZE for higher precision */ + unsigned long ratio = (vm_dirty_ratio * PAGE_SIZE) / 100; + unsigned long bg_ratio = (dirty_background_ratio * PAGE_SIZE) / 100; unsigned long thresh; unsigned long bg_thresh; struct task_struct *tsk; @@ -386,26 +387,28 @@ static void domain_dirty_limits(struct dirty_throttle_control *dtc) /* * The byte settings can't be applied directly to memcg * domains. Convert them to ratios by scaling against - * globally available memory. + * globally available memory. As the ratios are in + * per-PAGE_SIZE, they can be obtained by dividing bytes by + * number of pages. */ if (bytes) - ratio = min(DIV_ROUND_UP(bytes, PAGE_SIZE) * 100 / - global_avail, 100UL); + ratio = min(DIV_ROUND_UP(bytes, global_avail), + PAGE_SIZE); if (bg_bytes) - bg_ratio = min(DIV_ROUND_UP(bg_bytes, PAGE_SIZE) * 100 / - global_avail, 100UL); + bg_ratio = min(DIV_ROUND_UP(bg_bytes, global_avail), + PAGE_SIZE); bytes = bg_bytes = 0; } if (bytes) thresh = DIV_ROUND_UP(bytes, PAGE_SIZE); else - thresh = (ratio * available_memory) / 100; + thresh = (ratio * available_memory) / PAGE_SIZE; if (bg_bytes) bg_thresh = DIV_ROUND_UP(bg_bytes, PAGE_SIZE); else - bg_thresh = (bg_ratio * available_memory) / 100; + bg_thresh = (bg_ratio * available_memory) / PAGE_SIZE; if (bg_thresh >= thresh) bg_thresh = thresh / 2; |