From 45a2966fd64147518dc5bca25f447bd0fb5359ac Mon Sep 17 00:00:00 2001 From: Jan Kara Date: Thu, 2 Sep 2021 14:53:09 -0700 Subject: writeback: fix bandwidth estimate for spiky workload Michael Stapelberg has reported that for workload with short big spikes of writes (GCC linker seem to trigger this frequently) the write throughput is heavily underestimated and tends to steadily sink until it reaches zero. This has rather bad impact on writeback throttling (causing stalls). The problem is that writeback throughput estimate gets updated at most once per 200 ms. One update happens early after we submit pages for writeback (at that point writeout of only small fraction of pages is completed and thus observed throughput is tiny). Next update happens only during the next write spike (updates happen only from inode writeback and dirty throttling code) and if that is more than 1s after previous spike, we decide system was idle and just ignore whatever was written until this moment. Fix the problem by making sure writeback throughput estimate is also updated shortly after writeback completes to get reasonable estimate of throughput for spiky workloads. [jack@suse.cz: avoid division by 0 in wb_update_dirty_ratelimit()] Link: https://lore.kernel.org/lkml/20210617095309.3542373-1-stapelberg+linux@google.com Link: https://lkml.kernel.org/r/20210713104716.22868-3-jack@suse.cz Signed-off-by: Jan Kara Reported-by: Michael Stapelberg Tested-by: Michael Stapelberg Cc: Wu Fengguang Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/writeback.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include/linux/writeback.h') diff --git a/include/linux/writeback.h b/include/linux/writeback.h index 2480322c06a7..cbaef099645e 100644 --- a/include/linux/writeback.h +++ b/include/linux/writeback.h @@ -379,6 +379,7 @@ int dirty_writeback_centisecs_handler(struct ctl_table *table, int write, void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty); unsigned long wb_calc_thresh(struct bdi_writeback *wb, unsigned long thresh); +void wb_update_bandwidth(struct bdi_writeback *wb); void balance_dirty_pages_ratelimited(struct address_space *mapping); bool wb_over_bg_thresh(struct bdi_writeback *wb); -- cgit v1.2.3