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

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Message-ID: <20171204230233.GQ2421075@devbig577.frc2.facebook.com>
Date:   Mon, 4 Dec 2017 15:02:33 -0800
From:   Tejun Heo <tj@...nel.org>
To:     Kirill Tkhai <ktkhai@...tuozzo.com>
Cc:     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, Kirill.

On Tue, Dec 05, 2017 at 01:49:42AM +0300, Kirill Tkhai wrote:
> > If the only reason is kernel memory consumption protection, the only
> > thing we need to do is making sure that memory used for aio commands
> > are accounted against cgroup kernel memory consumption and
> > relaxing/removing system wide limit.
> 
> So, we just use GFP_KERNEL_ACCOUNT flag for allocation of internal aio
> structures and pages, and all the memory will be accounted in kmem and
> limited by memcg. Looks very good.

Yeah.

> One detail about memory consumption. io_submit() calls primitives
> file_operations::write_iter and read_iter. It's not clear for me whether
> they consume the same memory as if writev() or readv() system calls
> would be used instead. writev() may delay the actual write till dirty
> pages limit will be reached, so it seems logic of the accounting should
> be the same. So aio mustn't use more not accounted system memory in file
> system internals, then simple writev().
> 
> Could you please to say if you have thoughts about this?

I'm not too familiar with vfs / filesystems but I don't think there's
gonna be significant unaccounted memory consumption.  It shouldn't be
too difficult to find out with experiments too.

Thanks.

-- 
tejun