From: NeilBrown Date: Thu, 29 Nov 2018 23:33:18 +0000 (+1100) Subject: VFS: use synchronize_rcu_expedited() in namespace_unlock() X-Git-Tag: Ubuntu-5.10.0-12.13~6243^2~2 X-Git-Url: https://git.proxmox.com/?a=commitdiff_plain;h=22cb7405fada5305926d9bbcb476c1cd638d2dab;p=mirror_ubuntu-hirsute-kernel.git VFS: use synchronize_rcu_expedited() in namespace_unlock() The synchronize_rcu() in namespace_unlock() is called every time a filesystem is unmounted. If a great many filesystems are mounted, this can cause a noticable slow-down in, for example, system shutdown. The sequence: mkdir -p /tmp/Mtest/{0..5000} time for i in /tmp/Mtest/*; do mount -t tmpfs tmpfs $i ; done time umount /tmp/Mtest/* on a 4-cpu VM can report 8 seconds to mount the tmpfs filesystems, and 100 seconds to unmount them. Boot the same VM with 1 CPU and it takes 18 seconds to mount the tmpfs filesystems, but only 36 to unmount. If we change the synchronize_rcu() to synchronize_rcu_expedited() the umount time on a 4-cpu VM drop to 0.6 seconds I think this 200-fold speed up is worth the slightly high system impact of using synchronize_rcu_expedited(). Acked-by: Paul E. McKenney (from general rcu perspective) Signed-off-by: NeilBrown Signed-off-by: Al Viro --- diff --git a/fs/namespace.c b/fs/namespace.c index 98d27da43304..9cd4fcc0de94 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1360,7 +1360,7 @@ static void namespace_unlock(void) if (likely(hlist_empty(&head))) return; - synchronize_rcu(); + synchronize_rcu_expedited(); group_pin_kill(&head); }