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

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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.

-- 
Mel Gorman
SUSE Labs

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[RFC 0/2] Use HighAtomic against long-term fragmentation Hui Zhu <zhuhui@xiaomi.com> - 2017-09-26 11:10 +0200
  [RFC 1/2] Try to use HighAtomic if try to alloc umovable page that order is not 0 Hui Zhu <zhuhui@xiaomi.com> - 2017-09-26 11:10 +0200
    Re: [RFC 1/2] Try to use HighAtomic if try to alloc umovable page  that order is not 0 Michal Hocko <mhocko@kernel.org> - 2017-09-26 12:50 +0200
  Re: [RFC 0/2] Use HighAtomic against long-term fragmentation Mel Gorman <mgorman@techsingularity.net> - 2017-09-26 12:00 +0200
    Re: [RFC 0/2] Use HighAtomic against long-term fragmentation Hui Zhu <teawater@gmail.com> - 2017-09-26 12:10 +0200
      Re: [RFC 0/2] Use HighAtomic against long-term fragmentation Mel Gorman <mgorman@techsingularity.net> - 2017-09-26 12:50 +0200

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