Commit 39ac9985 authored by Jim Zhao's avatar Jim Zhao Committed by Andrew Morton
Browse files

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.

Link: https://lkml.kernel.org/r/20241023100032.62952-1-jimzhao.ai@gmail.com


Signed-off-by: default avatarJim Zhao <jimzhao.ai@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 72237693

mm/page-writeback.c

+22 −3
Original line number Diff line number Diff line
@@ -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;

}