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>

1 files changed, 6 insertions, 0 deletions

diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index c5c1ebff1e2d..67aaf6ee38ea 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -296,6 +296,12 @@ struct fuse_conn {
         /** Number of requests currently in the background */
         unsigned num_background;
 
+        /** Number of background requests currently queued for userspace */
+        unsigned active_background;
+
+        /** The list of background requests set aside for later queuing */
+        struct list_head bg_queue;
+
         /** Pending interrupts */
         struct list_head interrupts;