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Message-Id: <20241023100032.62952-1-jimzhao.ai@gmail.com>
Date: Wed, 23 Oct 2024 18:00:32 +0800
From: Jim Zhao <jimzhao.ai@...il.com>
To: willy@...radead.org,
akpm@...ux-foundation.org
Cc: linux-fsdevel@...r.kernel.org,
linux-mm@...ck.org,
linux-kernel@...r.kernel.org,
Jim Zhao <jimzhao.ai@...il.com>
Subject: [PATCH] mm/page-writeback: Raise wb_thresh to prevent write blocking with strictlimit
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.
Signed-off-by: Jim Zhao <jimzhao.ai@...il.com>
---
mm/page-writeback.c | 25 ++++++++++++++++++++++---
1 file changed, 22 insertions(+), 3 deletions(-)
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 72a5d8836425..f21d856c408b 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -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;
}
--
2.34.1
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