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Date: Mon, 16 Oct 2017 23:19:02 +0100
From: Al Viro <viro@ZenIV.linux.org.uk>
To: Leon Yang <leon.gh.yang@gmail.com>
Cc: "open list:FILESYSTEMS (VFS and infrastructure)" 
        <linux-fsdevel@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] Batch unmount cleanup
Message-ID: <20171016221902.GM21978@ZenIV.linux.org.uk>
References: <1508179936-15591-1-git-send-email-leon.gh.yang@gmail.com>
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On Mon, Oct 16, 2017 at 01:52:16PM -0500, Leon Yang wrote:
> From: Leon Yang <leon.gh.yang@gmail.com>
> 
> Each time the unmounted list is cleanup, synchronize_rcu() is
> called, which is relatively costly. Scheduling the cleanup in a
> workqueue, similar to what is being done in
> net/core/net_namespace.c:cleanup_net, makes unmounting faster
> without adding too much overhead. This is useful especially for
> servers with many containers where mounting/unmounting happens a
> lot.

NAK.  You really do _not_ want to return from umount(2) too early.