linux-kernel - Re: [RFC 0/2] Use HighAtomic against long-term fragmentation

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Date:   Tue, 26 Sep 2017 18:04:04 +0800
From:   Hui Zhu <teawater@...il.com>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     Hui Zhu <zhuhui@...omi.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>, hillf.zj@...baba-inc.com,
        Linux Memory Management List <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 0/2] Use HighAtomic against long-term fragmentation

2017-09-26 17:51 GMT+08:00 Mel Gorman <mgorman@...hsingularity.net>:
> On Tue, Sep 26, 2017 at 04:46:42PM +0800, Hui Zhu wrote:
>> Current HighAtomic just to handle the high atomic page alloc.
>> But I found that use it handle the normal unmovable continuous page
>> alloc will help to against long-term fragmentation.
>>
>
> This is not wise. High-order atomic allocations do not always have a
> smooth recovery path such as network drivers with large MTUs that have no
> choice but to drop the traffic and hope for a retransmit. That's why they
> have the highatomic reserve. If the reserve is used for normal unmovable
> allocations then allocation requests that could have waited for reclaim
> may cause high-order atomic allocations to fail. Changing it may allow
> improve latencies in some limited cases while causing functional failures
> in others.  If there is a special case where there are a large number of
> other high-order allocations then I would suggest increasing min_free_kbytes
> instead as a workaround.

I think let 0 order unmovable page alloc and other order unmovable pages
alloc use different migrate types will help against long-term
fragmentation.

Do you think kernel can add a special migrate type for big than 0 order
unmovable pages alloc?

Thanks,
Hui

>
> --
> Mel Gorman
> SUSE Labs