fuse: limit queued background requests
Libfuse basically creates a new thread for each new request. This is fine for
synchronous requests, which are naturally limited. However background
requests (especially writepage) can cause a thread creation storm.
To avoid this, limit the number of background requests available to userspace.
This is done by introducing another queue for background requests, and a
counter for the number of "active" requests, which are currently available for
userspace.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index db534bc..af639807 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -201,6 +201,55 @@
}
}
+static unsigned len_args(unsigned numargs, struct fuse_arg *args)
+{
+ unsigned nbytes = 0;
+ unsigned i;
+
+ for (i = 0; i < numargs; i++)
+ nbytes += args[i].size;
+
+ return nbytes;
+}
+
+static u64 fuse_get_unique(struct fuse_conn *fc)
+{
+ fc->reqctr++;
+ /* zero is special */
+ if (fc->reqctr == 0)
+ fc->reqctr = 1;
+
+ return fc->reqctr;
+}
+
+static void queue_request(struct fuse_conn *fc, struct fuse_req *req)
+{
+ req->in.h.unique = fuse_get_unique(fc);
+ req->in.h.len = sizeof(struct fuse_in_header) +
+ len_args(req->in.numargs, (struct fuse_arg *) req->in.args);
+ list_add_tail(&req->list, &fc->pending);
+ req->state = FUSE_REQ_PENDING;
+ if (!req->waiting) {
+ req->waiting = 1;
+ atomic_inc(&fc->num_waiting);
+ }
+ wake_up(&fc->waitq);
+ kill_fasync(&fc->fasync, SIGIO, POLL_IN);
+}
+
+static void flush_bg_queue(struct fuse_conn *fc)
+{
+ while (fc->active_background < FUSE_MAX_BACKGROUND &&
+ !list_empty(&fc->bg_queue)) {
+ struct fuse_req *req;
+
+ req = list_entry(fc->bg_queue.next, struct fuse_req, list);
+ list_del(&req->list);
+ fc->active_background++;
+ queue_request(fc, req);
+ }
+}
+
/*
* This function is called when a request is finished. Either a reply
* has arrived or it was aborted (and not yet sent) or some error
@@ -229,6 +278,8 @@
clear_bdi_congested(&fc->bdi, WRITE);
}
fc->num_background--;
+ fc->active_background--;
+ flush_bg_queue(fc);
}
spin_unlock(&fc->lock);
wake_up(&req->waitq);
@@ -320,42 +371,6 @@
}
}
-static unsigned len_args(unsigned numargs, struct fuse_arg *args)
-{
- unsigned nbytes = 0;
- unsigned i;
-
- for (i = 0; i < numargs; i++)
- nbytes += args[i].size;
-
- return nbytes;
-}
-
-static u64 fuse_get_unique(struct fuse_conn *fc)
- {
- fc->reqctr++;
- /* zero is special */
- if (fc->reqctr == 0)
- fc->reqctr = 1;
-
- return fc->reqctr;
-}
-
-static void queue_request(struct fuse_conn *fc, struct fuse_req *req)
-{
- req->in.h.unique = fuse_get_unique(fc);
- req->in.h.len = sizeof(struct fuse_in_header) +
- len_args(req->in.numargs, (struct fuse_arg *) req->in.args);
- list_add_tail(&req->list, &fc->pending);
- req->state = FUSE_REQ_PENDING;
- if (!req->waiting) {
- req->waiting = 1;
- atomic_inc(&fc->num_waiting);
- }
- wake_up(&fc->waitq);
- kill_fasync(&fc->fasync, SIGIO, POLL_IN);
-}
-
void request_send(struct fuse_conn *fc, struct fuse_req *req)
{
req->isreply = 1;
@@ -375,20 +390,26 @@
spin_unlock(&fc->lock);
}
+static void request_send_nowait_locked(struct fuse_conn *fc,
+ struct fuse_req *req)
+{
+ req->background = 1;
+ fc->num_background++;
+ if (fc->num_background == FUSE_MAX_BACKGROUND)
+ fc->blocked = 1;
+ if (fc->num_background == FUSE_CONGESTION_THRESHOLD) {
+ set_bdi_congested(&fc->bdi, READ);
+ set_bdi_congested(&fc->bdi, WRITE);
+ }
+ list_add_tail(&req->list, &fc->bg_queue);
+ flush_bg_queue(fc);
+}
+
static void request_send_nowait(struct fuse_conn *fc, struct fuse_req *req)
{
spin_lock(&fc->lock);
if (fc->connected) {
- req->background = 1;
- fc->num_background++;
- if (fc->num_background == FUSE_MAX_BACKGROUND)
- fc->blocked = 1;
- if (fc->num_background == FUSE_CONGESTION_THRESHOLD) {
- set_bdi_congested(&fc->bdi, READ);
- set_bdi_congested(&fc->bdi, WRITE);
- }
-
- queue_request(fc, req);
+ request_send_nowait_locked(fc, req);
spin_unlock(&fc->lock);
} else {
req->out.h.error = -ENOTCONN;