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Date:   Wed, 21 Feb 2018 11:57:47 -0600 (CST)
From:   Christopher Lameter <cl@linux.com>
To:     Shakeel Butt <shakeelb@google.com>
cc:     Jan Kara <jack@suse.cz>, Amir Goldstein <amir73il@gmail.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Greg Thelen <gthelen@google.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Mel Gorman <mgorman@suse.de>, Vlastimil Babka <vbabka@suse.cz>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Linux MM <linux-mm@kvack.org>,
        Cgroups <cgroups@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 0/3] Directed kmem charging
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On Wed, 21 Feb 2018, Shakeel Butt wrote:

> On Wed, Feb 21, 2018 at 8:09 AM, Christopher Lameter <cl@linux.com> wrote:
> > Another way to solve this is to switch the user context right?
> >
> > Isnt it possible to avoid these patches if do the allocation in another
> > task context instead?
> >
>
> Sorry, can you please explain what you mean by 'switch the user
> context'. Is there any example in kernel which does something similar?

See include/linux/task_work.h. One use case is in mntput_no_expire() in
linux/fs/namespace.c

> > Are there really any other use cases beyond fsnotify?
> >
>
> Another use case I have in mind and plan to upstream is to bind a
> filesystem mount with a memcg. So, all the file pages (or anon pages
> for shmem) and kmem (like inodes and dentry) will be charged to that
> memcg.

The mount logic already uses task_work.h. That may be the approach to
expand there.