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authorNeilBrown <neilb@suse.com>2018-11-30 10:33:18 +1100
committerAl Viro <viro@zeniv.linux.org.uk>2018-11-29 18:55:10 -0500
commit22cb7405fada5305926d9bbcb476c1cd638d2dab (patch)
treec21cde60f75baa4f607d8d04ffd22ba7fb30b9ad /fs
parent651022382c7f8da46cb4872a545ee1da6d097d2a (diff)
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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 <paulmck@linux.vnet.ibm.com> (from general rcu perspective) Signed-off-by: NeilBrown <neilb@suse.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Diffstat (limited to 'fs')
-rw-r--r--fs/namespace.c2
1 files changed, 1 insertions, 1 deletions
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);
}