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Subject: Re: [PATCH 5/8] mm, page_alloc: make THP-specific decisions more
 generic
References: <20160718112302.27381-1-vbabka@suse.cz>
 <20160718112302.27381-6-vbabka@suse.cz>
 <alpine.DEB.2.10.1607191608550.19940@chino.kir.corp.google.com>
From: Vlastimil Babka <vbabka@suse.cz>
Message-ID: <59bfd68b-2333-d762-6bc1-5f156e83c3d3@suse.cz>
Date: Thu, 21 Jul 2016 09:13:39 +0200
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To: David Rientjes <rientjes@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Michal Hocko <mhocko@kernel.org>, Mel Gorman <mgorman@techsingularity.net>, Joonsoo Kim <iamjoonsoo.kim@lge.com>, Rik van Riel <riel@redhat.com>

On 07/20/2016 01:10 AM, David Rientjes wrote:
> On Mon, 18 Jul 2016, Vlastimil Babka wrote:
>
>> This means we can further distinguish allocations that are costly order *and*
>> additionally include the __GFP_NORETRY flag. As it happens, GFP_TRANSHUGE
>> allocations do already fall into this category. This will also allow other
>> costly allocations with similar high-order benefit vs latency considerations to
>> use this semantic. Furthermore, we can distinguish THP allocations that should
>> try a bit harder (such as from khugepageed) by removing __GFP_NORETRY, as will
>> be done in the next patch.
>>
>> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
>> Acked-by: Michal Hocko <mhocko@suse.com>
>
> I think this is fine, but I would hope that we could check
> gfp_pfmemalloc_allowed() before compacting and failing even for costly
> orders when otherwise the first get_page_from_freelist() in the slowpath
> may have succeeded due to watermarks.

Hm ok, I will add it for the sake of avoiding goto nopage where 
previously it would have tried alloc without watermarks, as that would 
be unintended side-effect of the series... although I have some doubts 
about sanity of such scenarios (wants a costly order, can 
reclaim/compact but only with __GFP_NORETRY, yet is allowed to avoid 
watermarks?). Do you know about examples of such callers and think they 
do the right thing?

Thanks,
Vlastimil

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