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>,
linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
Josh Triplett <josh@joshtriplett.org>
Subject: Re: [PATCH - resend] VFS: use synchronize_rcu_expedited() in namespace_unlock()
Date: Tue, 06 Nov 2018 14:15:35 +1100 [thread overview]
Message-ID: <87tvkuyjzc.fsf@notabene.neil.brown.name> (raw)
In-Reply-To: <87tvm1rxme.fsf@notabene.neil.brown.name>
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On Fri, Oct 05 2018, NeilBrown wrote:
> 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....
Hi Al,
this isn't in 4.20-rc1. Are you still waiting for something?
Thanks,
NeilBrown
>
> 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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prev parent reply other threads:[~2018-11-06 12:38 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 ` [PATCH - resend] " NeilBrown
2018-10-05 1:40 ` 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 ` NeilBrown [this message]
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