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 <mpatlasov@parallels.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
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 @@
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 @@
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 @@
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 @@
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);