linux-kernel - Re: [PATCH 1/4] mm, page_alloc: add likely macro to help compiler optimization

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Message-ID: <20130802204710.GX715@cmpxchg.org>
Date:	Fri, 2 Aug 2013 16:47:10 -0400
From:	Johannes Weiner <hannes@...xchg.org>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Joonsoo Kim <js1304@...il.com>,
	Minchan Kim <minchan@...nel.org>, Mel Gorman <mgorman@...e.de>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH 1/4] mm, page_alloc: add likely macro to help compiler
 optimization

On Fri, Aug 02, 2013 at 06:27:22PM +0200, Michal Hocko wrote:
> On Fri 02-08-13 11:07:56, Joonsoo Kim wrote:
> > We rarely allocate a page with ALLOC_NO_WATERMARKS and it is used
> > in slow path. For making fast path more faster, add likely macro to
> > help compiler optimization.
> 
> The code is different in mmotm tree (see mm: page_alloc: rearrange
> watermark checking in get_page_from_freelist)

Yes, please rebase this on top.

> Besides that, make sure you provide numbers which prove your claims
> about performance optimizations.

Isn't that a bit overkill?  We know it's a likely path (we would
deadlock constantly if a sizable portion of allocations were to ignore
the watermarks).  Does he have to justify that likely in general makes
sense?
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