linux-kernel - Re: Bloat caused by unnecessary calls to compound

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Message-ID: <20160327204413.GB9638@node.shutemov.name>
Date:	Sun, 27 Mar 2016 23:44:13 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	George Spelvin <linux@...izon.com>
Cc:	ebiggers3@...il.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: Bloat caused by unnecessary calls to compound_head()?

On Sun, Mar 27, 2016 at 04:33:04PM -0400, George Spelvin wrote:
> Could you just mark compound_head __pure?  That would tell the compiler
> that it's safe to re-use the return value as long as there is no memory
> mutation in between.
> 

Hm. It has some positive impact, but it's not dramatic. For instance,
mm/swap.o results:

add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-43 (-43)
function                                     old     new   delta
__page_cache_release                         319     298     -21
release_pages                                722     700     -22

mark_page_accessed() problem was not fixed by that.

-- 
 Kirill A. Shutemov