linux-kernel - Re: [PATCH 0/5] blkcg: Limit maximum number of aio requests available for cgroup

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Date:   Tue, 5 Dec 2017 07:51:25 -0800
From:   Tejun Heo <tj@...nel.org>
To:     Jeff Moyer <jmoyer@...hat.com>
Cc:     Kirill Tkhai <ktkhai@...tuozzo.com>, axboe@...nel.dk,
        bcrl@...ck.org, viro@...iv.linux.org.uk,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-aio@...ck.org, oleg@...hat.com
Subject: Re: [PATCH 0/5] blkcg: Limit maximum number of aio requests
 available for cgroup

Hello, Jeff.

On Tue, Dec 05, 2017 at 10:41:11AM -0500, Jeff Moyer wrote:
> Kirill Tkhai <ktkhai@...tuozzo.com> writes:
> 
> >> I think you just need to account the completion ring.
> >
> > A request of struct aio_kiocb type consumes much more memory, than
> > struct io_event does. Shouldn't we account it too?
> 
> Not in my opinion.  The completion ring is the part that gets pinned for
> long periods of time.

For memcg, it should account all possibly significant memory
consumptions whether long term or transitional.  Otherwise, isolation
doesn't really work that well.

> Just be sure to document this where appropriate.  Users/admins should
> know that the aio completion ring now contributes to their memory
> budget.

Yeah, the memory section in cgroup-v2.txt does have a section for
this.

Thanks.

-- 
tejun