linux-kernel - Re: [PATCH RFC] mnt: umount mounts one by one in umount

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Message-ID: <87wp8ec3lc.fsf@xmission.com>
Date:   Wed, 14 Jun 2017 04:37:19 -0500
From:   ebiederm@...ssion.com (Eric W. Biederman)
To:     Ian Kent <raven@...maw.net>
Cc:     Andrei Vagin <avagin@...nvz.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Linux Containers <containers@...ts.linux-foundation.org>
Subject: Re: [PATCH RFC] mnt: umount mounts one by one in umount_tree()

Ian Kent <raven@...maw.net> writes:

> On Fri, 2017-05-12 at 00:08 -0700, Andrei Vagin wrote:
>> With this patch, we don't try to umount all mounts of a tree together.
>> Instead of this we umount them one by one. In this case, we see a significant
>> improvement in performance for the worsе case.
>
> Indeed, umount has been very slow for a while now.
> Even a moderately large number of mounts (~10000) become painfully slow.
>
> Re you still perusing this?
> Anything I can do to help?
>
> Eric, what are your thoughts on this latest attempt?

I have something slightly more recent.  Please checkout my for-next
branch of my userns tree:

git://git.kernel.org/pub/scm/linux/kernel/git/ebiederm/user-namespace.git for-next

There is one open area of semantics that I looking at with Ram Pai in
the hopes we can drive consensus before we take any patches for
better checkpoint-restart support.

Eric