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mm/page-writeback: raise wb_thresh to prevent write blocking with strictlimit

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With the strictlimit flag, wb_thresh acts as a hard limit in
balance_dirty_pages() and wb_position_ratio().  When device write
operations are inactive, wb_thresh can drop to 0, causing writes to be
blocked.  The issue occasionally occurs in fuse fs, particularly with
network backends, the write thread is blocked frequently during a period. 
To address it, this patch raises the minimum wb_thresh to a controllable
level, similar to the non-strictlimit case.

Link: https://lkml.kernel.org/r/20241023100032.62952-1-jimzhao.ai@gmail.com
Signed-off-by: Jim Zhao <jimzhao.ai@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Jim Zhao 2024-10-23 18:00:32 +08:00 committed by Andrew Morton
parent 722376934b
commit 39ac99852f
1 changed files with 22 additions and 3 deletions
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25
mm/page-writeback.c
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@ -917,7 +917,9 @@ static unsigned long __wb_calc_thresh(struct dirty_throttle_control *dtc,
unsigned long thresh)
{
struct wb_domain *dom = dtc_dom(dtc);
struct bdi_writeback *wb = dtc->wb;
u64 wb_thresh;
u64 wb_max_thresh;
unsigned long numerator, denominator;
unsigned long wb_min_ratio, wb_max_ratio;
@ -931,11 +933,28 @@ static unsigned long __wb_calc_thresh(struct dirty_throttle_control *dtc,
wb_thresh *= numerator;
wb_thresh = div64_ul(wb_thresh, denominator);
wb_min_max_ratio(dtc->wb, &wb_min_ratio, &wb_max_ratio);
wb_min_max_ratio(wb, &wb_min_ratio, &wb_max_ratio);
wb_thresh += (thresh * wb_min_ratio) / (100 * BDI_RATIO_SCALE);
if (wb_thresh > (thresh * wb_max_ratio) / (100 * BDI_RATIO_SCALE))
wb_thresh = thresh * wb_max_ratio / (100 * BDI_RATIO_SCALE);
wb_max_thresh = thresh * wb_max_ratio / (100 * BDI_RATIO_SCALE);
if (wb_thresh > wb_max_thresh)
wb_thresh = wb_max_thresh;
/*
* With strictlimit flag, the wb_thresh is treated as
* a hard limit in balance_dirty_pages() and wb_position_ratio().
* It's possible that wb_thresh is close to zero, not because
* the device is slow, but because it has been inactive.
* To prevent occasional writes from being blocked, we raise wb_thresh.
*/
if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
unsigned long limit = hard_dirty_limit(dom, dtc->thresh);
u64 wb_scale_thresh = 0;
if (limit > dtc->dirty)
wb_scale_thresh = (limit - dtc->dirty) / 100;
wb_thresh = max(wb_thresh, min(wb_scale_thresh, wb_max_thresh / 4));
}
return wb_thresh;
}