linux-kernel - Re: [PATCH 3/8] mm, page_alloc: don't retry initial attempt in slowpath

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Message-ID: <6a427871-c1fb-77e7-2f45-1c4be436fa23@suse.cz>
Date:	Mon, 18 Jul 2016 13:34:29 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Michal Hocko <mhocko@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Mel Gorman <mgorman@...hsingularity.net>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	David Rientjes <rientjes@...gle.com>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 3/8] mm, page_alloc: don't retry initial attempt in
 slowpath

On 07/18/2016 01:29 PM, Michal Hocko wrote:
> On Mon 18-07-16 13:22:57, Vlastimil Babka wrote:
>> After __alloc_pages_slowpath() sets up new alloc_flags and wakes up kswapd, it
>> first tries get_page_from_freelist() with the new alloc_flags, as it may
>> succeed e.g. due to using min watermark instead of low watermark. It makes
>> sense to to do this attempt before adjusting zonelist based on
>> alloc_flags/gfp_mask, as it's still relatively a fast path if we just wake up
>> kswapd and successfully allocate.
>>
>> This patch therefore moves the initial attempt above the retry label and
>> reorganizes a bit the part below the retry label. We still have to attempt
>> get_page_from_freelist() on each retry, as some allocations cannot do that
>> as part of direct reclaim or compaction, and yet are not allowed to fail
>> (even though they do a WARN_ON_ONCE() and thus should not exist). We can reuse
>> the call meant for ALLOC_NO_WATERMARKS attempt and just set alloc_flags to
>> ALLOC_NO_WATERMARKS if the context allows it. As a side-effect, the attempts
>> from direct reclaim/compaction will also no longer obey watermarks once this
>> is set, but there's little harm in that.
>>
>> Kswapd wakeups are also done on each retry to be safe from potential races
>> resulting in kswapd going to sleep while a process (that may not be able to
>> reclaim by itself) is still looping.
>>
>> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
>
> Same here, my ack still holds
> Acked-by: Michal Hocko <mhocko@...e.com>

Sorry, forgot to add them before sending. Thanks for both!