From: NeilBrown <neilb@suse.com>
To: Alexander Viro <viro@zeniv.linux.org.uk>,
Andrew Morton <akpm@linux-foundation.org>
Cc: paulmck@linux.vnet.ibm.com, Florian Weimer <fweimer@redhat.com>
Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
Josh Triplett <josh@joshtriplett.org>
Subject: [PATCH - resend] VFS: use synchronize_rcu_expedited() in namespace_unlock()
Date: Fri, 05 Oct 2018 11:27:37 +1000 [thread overview]
Message-ID: <87tvm1rxme.fsf@notabene.neil.brown.name> (raw)
In-Reply-To: <87induxd3u.fsf@notabene.neil.brown.name>
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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>
---
I posted this last October, then again last November (cc:ing Linus)
Paul is happy enough with it, but no other response.
I'm hoping it can get applied this time....
Thanks,
NeilBrown
fs/namespace.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/namespace.c b/fs/namespace.c
index 99186556f8d3..02e978b22294 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);
}
--
2.14.0.rc0.dirty
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next prev parent reply other threads:[~2018-10-05 8:24 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-26 2:26 [PATCH] VFS: use synchronize_rcu_expedited() in namespace_unlock() NeilBrown
2017-10-26 12:27 ` Paul E. McKenney
2017-10-26 13:50 ` Paul E. McKenney
2017-10-27 0:45 ` NeilBrown
2017-10-27 1:24 ` Paul E. McKenney
2017-11-27 11:27 ` Florian Weimer
2017-11-27 14:41 ` Paul E. McKenney
2017-11-28 22:17 ` NeilBrown
2018-10-05 1:27 ` NeilBrown [this message]
2018-10-05 1:40 ` [PATCH - resend] " Al Viro
2018-10-05 2:53 ` NeilBrown
2018-10-05 4:08 ` Paul E. McKenney
2018-11-29 23:33 ` [PATCH - resend*2] " NeilBrown
2018-11-29 23:52 ` Al Viro
2018-11-30 1:09 ` NeilBrown
2018-11-06 3:15 ` [PATCH - resend] " NeilBrown
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