From 722d2bea8c601d0744e4a37170533fdf6214a678 Mon Sep 17 00:00:00 2001 From: Maxim Patlasov Date: Thu, 21 Mar 2013 18:02:36 +0400 Subject: [PATCH] fuse: implement exclusive wakeup for blocked_waitq The patch solves thundering herd problem. So far as previous patches ensured that only allocations for background may block, it's safe to wake up one waiter. Whoever it is, it will wake up another one in request_end() afterwards. Signed-off-by: Maxim Patlasov Signed-off-by: Miklos Szeredi --- fs/fuse/dev.c | 29 ++++++++++++++++++++++++----- 1 file changed, 24 insertions(+), 5 deletions(-) diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c index d692b85..3673105 100644 --- a/fs/fuse/dev.c +++ b/fs/fuse/dev.c @@ -147,7 +147,7 @@ static struct fuse_req *__fuse_get_req(struct fuse_conn *fc, unsigned npages, int intr; block_sigs(&oldset); - intr = wait_event_interruptible(fc->blocked_waitq, + intr = wait_event_interruptible_exclusive(fc->blocked_waitq, !fuse_block_alloc(fc, for_background)); restore_sigs(&oldset); err = -EINTR; @@ -161,8 +161,11 @@ static struct fuse_req *__fuse_get_req(struct fuse_conn *fc, unsigned npages, req = fuse_request_alloc(npages); err = -ENOMEM; - if (!req) + if (!req) { + if (for_background) + wake_up(&fc->blocked_waitq); goto out; + } fuse_req_init_context(req); req->waiting = 1; @@ -262,6 +265,17 @@ struct fuse_req *fuse_get_req_nofail_nopages(struct fuse_conn *fc, void fuse_put_request(struct fuse_conn *fc, struct fuse_req *req) { if (atomic_dec_and_test(&req->count)) { + if (unlikely(req->background)) { + /* + * We get here in the unlikely case that a background + * request was allocated but not sent + */ + spin_lock(&fc->lock); + if (!fc->blocked) + wake_up(&fc->blocked_waitq); + spin_unlock(&fc->lock); + } + if (req->waiting) atomic_dec(&fc->num_waiting); @@ -359,10 +373,15 @@ __releases(fc->lock) list_del(&req->intr_entry); req->state = FUSE_REQ_FINISHED; if (req->background) { - if (fc->num_background == fc->max_background) { + req->background = 0; + + if (fc->num_background == fc->max_background) fc->blocked = 0; - wake_up_all(&fc->blocked_waitq); - } + + /* Wake up next waiter, if any */ + if (!fc->blocked) + wake_up(&fc->blocked_waitq); + if (fc->num_background == fc->congestion_threshold && fc->connected && fc->bdi_initialized) { clear_bdi_congested(&fc->bdi, BLK_RW_SYNC); -- 2.7.4