Subject: Re: [PATCH 0/5] blkcg: Limit maximum number of aio requests available
 for cgroup
To: Tejun Heo <tj@kernel.org>
Cc: axboe@kernel.dk, bcrl@kvack.org, viro@zeniv.linux.org.uk,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-aio@kvack.org, oleg@redhat.com
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From: Kirill Tkhai <ktkhai@virtuozzo.com>
Message-ID: <5d3d5f20-1800-b7b2-14c5-895aa4632f2a@virtuozzo.com>
Date: Tue, 5 Dec 2017 02:05:30 +0300
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On 05.12.2017 02:02, Tejun Heo wrote:
> 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.

Thanks, Tejun!

Kirill