From 39ac99852fca98ca44d52716d792dfaf24981f53 Mon Sep 17 00:00:00 2001 From: Jim Zhao Date: Wed, 23 Oct 2024 18:00:32 +0800 Subject: 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: Jim Zhao Cc: Matthew Wilcox Signed-off-by: Andrew Morton --- mm/page-writeback.c | 25 ++++++++++++++++++++++--- 1 file changed, 22 insertions(+), 3 deletions(-) (limited to 'mm/page-writeback.c') diff --git a/mm/page-writeback.c b/mm/page-writeback.c index fcd4c1439cb9..1d7179aba8e3 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; } -- cgit