linux-kernel - Re: [PATCH 1/3] mm, page_alloc: un-inline the bad part of free_pages

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Message-ID: <5720B643.6060908@suse.cz>
Date:	Wed, 27 Apr 2016 14:53:23 +0200
From:	Vlastimil Babka <vbabka@...e.cz>
To:	Mel Gorman <mgorman@...hsingularity.net>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Jesper Dangaard Brouer <brouer@...hat.com>
Subject: Re: [PATCH 1/3] mm, page_alloc: un-inline the bad part of
 free_pages_check

On 04/27/2016 02:37 PM, Mel Gorman wrote:
> On Wed, Apr 27, 2016 at 02:01:14PM +0200, Vlastimil Babka wrote:
>> !DEBUG_VM bloat-o-meter:
>>
>> add/remove: 1/0 grow/shrink: 0/2 up/down: 124/-383 (-259)
>> function                                     old     new   delta
>> free_pages_check_bad                           -     124    +124
>> free_pcppages_bulk                          1509    1403    -106
>> __free_pages_ok                             1025     748    -277
>>
>> DEBUG_VM:
>>
>> add/remove: 1/0 grow/shrink: 0/1 up/down: 124/-242 (-118)
>> function                                     old     new   delta
>> free_pages_check_bad                           -     124    +124
>> free_pages_prepare                          1048     806    -242
>>
>> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
>
> This uninlines the check all right but it also introduces new function
> calls into the free path. As it's the free fast path, I suspect it would
> be a step in the wrong direction from a performance perspective.

Oh expected this to be a non-issue as the call only happens when a bad 
page is actually encountered, which is rare? But if you can measure some 
overhead here then sure.