linux-kernel - Re: [GIT PULL] cgroup changes for v4.18-rc1

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Date:   Wed, 6 Jun 2018 08:22:26 -0700
From:   Tejun Heo <tj@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Li Zefan <lizefan@...wei.com>,
        Johannes Weiner <hannes@...xchg.org>,
        cgroups <cgroups@...r.kernel.org>
Subject: Re: [GIT PULL] cgroup changes for v4.18-rc1

On Wed, Jun 06, 2018 at 08:14:27AM -0700, Linus Torvalds wrote:
> On Wed, Jun 6, 2018 at 8:04 AM Tejun Heo <tj@...nel.org> wrote:
> >
> > The notification implementation isn't super light weight, so the patch
> > ratelimits the notifications by capping minimum notification interval
> > interval to 10ms.
> 
> Yeah, I looked at the patch (and the code) to make sense of the explanation.
> 
> My reaction to that was that it might be a better idea to simply not
> notify if a notification was already pending, rather than have the
> timeout. Or perhaps in addition to. The path _to_ the fsnotify code
> looked quite messy, though.

Yeah, getting to the inode is currently quite involved.  Some of the
complications come from the fact that a kernfs node can be associated
with multiple inodes for sysfs namespace support.

The right thing to do could be linking the inodes to the kernfs node
and protect it with a spinlock so that we don't have to punt and walk
them directly from notification path.

For now, I think the 10ms thing is an acceptable workaround but this
likely needs more work in the future.

Thanks.

-- 
tejun