From d1dbc59200b54944f00251ca4dfbb2b318beca13 Mon Sep 17 00:00:00 2001 From: Baokun Li Date: Sat, 1 Aug 2026 16:24:51 +0800 Subject: [PATCH] fuse: wake one waiter per freed slot when raising max_background MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit fuse_get_req() parks background allocations on fch->blocked_waitq via wait_event_state_exclusive(), so each wakeup releases exactly one waiter. fuse_chan_max_background_set() clears fch->blocked when the new limit exceeds num_background, but the accompanying wake_up() releases a single waiter regardless of how many slots just became available. Raising max_background from 10 to 100 therefore admits one request instead of ninety. The remaining waiters are not permanently stranded — the "else if (!fch->blocked)" branch in fuse_request_end() wakes one more per completion — but that only helps while requests keep completing. Consider a fixed pool of threads doing readahead or async direct I/O with the quota exhausted: every thread is either in flight or parked, and each completion wakes one waiter while freeing one slot, a net change of zero. num_background oscillates around the old limit and the added quota is never taken up. Waking one waiter per freed slot also preserves submission order: once fch->blocked is clear, new callers of fuse_get_req() skip the waitqueue entirely, overtaking waiters that parked before the limit was raised. Use wake_up_nr() with the number of slots that just became available. Since the wakeup is guarded by !fch->blocked, num_background is strictly below max_background, so the count is at least 1 and never degenerates into wake_up_all(). Signed-off-by: Baokun Li Reviewed-By: Horst Birthelmer Signed-off-by: Miklos Szeredi --- fs/fuse/dev.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c index 3f498630f421..4fec31fc0b84 100644 --- a/fs/fuse/dev.c +++ b/fs/fuse/dev.c @@ -406,7 +406,8 @@ void fuse_chan_max_background_set(struct fuse_chan *fch, unsigned int val) fch->max_background = val; fch->blocked = fch->num_background >= fch->max_background; if (!fch->blocked) - wake_up(&fch->blocked_waitq); + wake_up_nr(&fch->blocked_waitq, + fch->max_background - fch->num_background); spin_unlock(&fch->bg_lock); }