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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: 9fc3a43e17
("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>
This commit is contained in:
parent
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@ -373,8 +373,9 @@ static void domain_dirty_limits(struct dirty_throttle_control *dtc)
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struct dirty_throttle_control *gdtc = mdtc_gdtc(dtc);
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unsigned long bytes = vm_dirty_bytes;
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unsigned long bg_bytes = dirty_background_bytes;
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unsigned long ratio = vm_dirty_ratio;
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unsigned long bg_ratio = dirty_background_ratio;
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/* convert ratios to per-PAGE_SIZE for higher precision */
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unsigned long ratio = (vm_dirty_ratio * PAGE_SIZE) / 100;
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unsigned long bg_ratio = (dirty_background_ratio * PAGE_SIZE) / 100;
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unsigned long thresh;
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unsigned long bg_thresh;
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struct task_struct *tsk;
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@ -386,26 +387,28 @@ static void domain_dirty_limits(struct dirty_throttle_control *dtc)
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/*
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* The byte settings can't be applied directly to memcg
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* domains. Convert them to ratios by scaling against
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* globally available memory.
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* globally available memory. As the ratios are in
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* per-PAGE_SIZE, they can be obtained by dividing bytes by
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* number of pages.
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*/
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if (bytes)
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ratio = min(DIV_ROUND_UP(bytes, PAGE_SIZE) * 100 /
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global_avail, 100UL);
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ratio = min(DIV_ROUND_UP(bytes, global_avail),
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PAGE_SIZE);
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if (bg_bytes)
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bg_ratio = min(DIV_ROUND_UP(bg_bytes, PAGE_SIZE) * 100 /
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global_avail, 100UL);
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bg_ratio = min(DIV_ROUND_UP(bg_bytes, global_avail),
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PAGE_SIZE);
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bytes = bg_bytes = 0;
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}
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if (bytes)
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thresh = DIV_ROUND_UP(bytes, PAGE_SIZE);
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else
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thresh = (ratio * available_memory) / 100;
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thresh = (ratio * available_memory) / PAGE_SIZE;
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if (bg_bytes)
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bg_thresh = DIV_ROUND_UP(bg_bytes, PAGE_SIZE);
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else
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bg_thresh = (bg_ratio * available_memory) / 100;
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bg_thresh = (bg_ratio * available_memory) / PAGE_SIZE;
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if (bg_thresh >= thresh)
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bg_thresh = thresh / 2;
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