Re: [PATCH] Batch unmount cleanup

[Al Viro]

On Mon, Oct 16, 2017 at 01:52:16PM -0500, Leon Yang wrote:
> From: Leon Yang <leon.gh.yang@xxxxxxxxx>
> 
> 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.