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author | NeilBrown <neilb@suse.com> | 2018-11-30 10:33:18 +1100 |
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committer | Al Viro <viro@zeniv.linux.org.uk> | 2018-11-29 18:55:10 -0500 |
commit | 22cb7405fada5305926d9bbcb476c1cd638d2dab (patch) | |
tree | c21cde60f75baa4f607d8d04ffd22ba7fb30b9ad /fs | |
parent | 651022382c7f8da46cb4872a545ee1da6d097d2a (diff) | |
download | linux-22cb7405fada5305926d9bbcb476c1cd638d2dab.tar.gz linux-22cb7405fada5305926d9bbcb476c1cd638d2dab.tar.bz2 linux-22cb7405fada5305926d9bbcb476c1cd638d2dab.zip |
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.c | 2 |
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); } |