diff options
| author | Joanne Koong <joannelkoong@gmail.com> | 2026-03-27 02:46:29 +0300 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2026-04-27 15:54:24 +0300 |
| commit | 0437906841d0448121a7907b71b73c6cf2fc7afb (patch) | |
| tree | 94a58117c298a368f91473fef9c2f79e7d4111b0 | |
| parent | 9ec95329894864170a1a7685b9a11b739393131a (diff) | |
| download | linux-0437906841d0448121a7907b71b73c6cf2fc7afb.tar.xz | |
mm: start background writeback based on per-wb threshold for strictlimit BDIs
The proactive nr_dirty > gdtc->bg_thresh check in balance_dirty_pages()
only checks the global dirty threshold to start background writeback while
the writer is still free-running, but for strictlimit BDIs (eg fuse), the
per-wb dirty count can exceed the per-wb background threshold while the
global threshold is not yet exceeded, so background writeback for this
case never gets proactively started.
Add a per-wb threshold check for strictlimit BDIs so that background
writeback is started when wb_dirty exceeds wb_bg_thresh, which drains
dirty pages before the writer hits the throttle wall, matching the
proactive behavior that the global check provides for non-strictlimit
BDIs.
fio runs on fuse show about a 3-4% improvement in perf for buffered
writes:
fio --name=writeback_test --ioengine=psync --rw=write --bs=128k \
--size=2G --numjobs=4 --ramp_time=10 --runtime=20 \
--time_based --group_reporting=1 --direct=0
Link: https://lore.kernel.org/20260326234629.840938-2-joannelkoong@gmail.com
Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
| -rw-r--r-- | mm/page-writeback.c | 16 |
1 files changed, 6 insertions, 10 deletions
diff --git a/mm/page-writeback.c b/mm/page-writeback.c index 88cd53d4ba09..833f743f309f 100644 --- a/mm/page-writeback.c +++ b/mm/page-writeback.c @@ -1835,7 +1835,9 @@ static int balance_dirty_pages(struct bdi_writeback *wb, balance_domain_limits(mdtc, strictlimit); } - if (nr_dirty > gdtc->bg_thresh && !writeback_in_progress(wb)) + if (!writeback_in_progress(wb) && + (nr_dirty > gdtc->bg_thresh || + (strictlimit && gdtc->wb_dirty > gdtc->wb_bg_thresh))) wb_start_background_writeback(wb); /* @@ -1862,15 +1864,9 @@ free_running: * Unconditionally start background writeback if it's not * already in progress. We need to do this because the global * dirty threshold check above (nr_dirty > gdtc->bg_thresh) - * doesn't account for these cases: - * - * a) strictlimit BDIs: throttling is calculated using per-wb - * thresholds. The per-wb threshold can be exceeded even when - * nr_dirty < gdtc->bg_thresh - * - * b) memcg-based throttling: memcg uses its own dirty count and - * thresholds and can trigger throttling even when global - * nr_dirty < gdtc->bg_thresh + * doesn't account for the memcg-based throttling case. memcg + * uses its own dirty count and thresholds and can trigger + * throttling even when global nr_dirty < gdtc->bg_thresh * * Writeback needs to be started else the writer stalls in the * throttle loop waiting for dirty pages to be written back |