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, 1 insertions, 0 deletions

diff --git a/fs/fuse/inode.c b/fs/fuse/inode.c
index e5e80d1a4687..c90f633d0b57 100644
--- a/fs/fuse/inode.c
+++ b/fs/fuse/inode.c
@@ -465,6 +465,7 @@ static struct fuse_conn *new_conn(void)
                 INIT_LIST_HEAD(&fc->processing);
                 INIT_LIST_HEAD(&fc->io);
                 INIT_LIST_HEAD(&fc->interrupts);
+                INIT_LIST_HEAD(&fc->bg_queue);
                 atomic_set(&fc->num_waiting, 0);
                 fc->bdi.ra_pages = (VM_MAX_READAHEAD * 1024) / PAGE_CACHE_SIZE;
                 fc->bdi.unplug_io_fn = default_unplug_io_fn;