The patch titled
Subject: mm/page-writeback: raise wb_thresh to prevent write blocking with strictlimit
has been added to the -mm mm-unstable branch. Its filename is
mm-page-writeback-raise-wb_thresh-to-prevent-write-blocking-with-strictlimit.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-page-writeback-raise-wb_thresh-to-prevent-write-blocking-with-strictlimit.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Before you just go and hit "reply", please:
a) Consider who else should be cc'ed
b) Prefer to cc a suitable mailing list as well
c) Ideally: find the original patch on the mailing list and do a
reply-to-all to that, adding suitable additional cc's
*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
The -mm tree is included into linux-next via the mm-everything
branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days
------------------------------------------------------
From: Jim Zhao <jimzhao.ai@xxxxxxxxx>
Subject: mm/page-writeback: raise wb_thresh to prevent write blocking with strictlimit
Date: Wed, 23 Oct 2024 18:00:32 +0800
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@xxxxxxxxx
Signed-off-by: Jim Zhao <jimzhao.ai@xxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page-writeback.c | 25 ++++++++++++++++++++++---
1 file changed, 22 insertions(+), 3 deletions(-)
--- a/mm/page-writeback.c~mm-page-writeback-raise-wb_thresh-to-prevent-write-blocking-with-strictlimit
+++ a/mm/page-writeback.c
@@ -917,7 +917,9 @@ static unsigned long __wb_calc_thresh(st
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(st
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;
}
_
Patches currently in -mm which might be from jimzhao.ai@xxxxxxxxx are
mm-page-writeback-raise-wb_thresh-to-prevent-write-blocking-with-strictlimit.patch
