linux-kernel - Re: [PATCH] mm/filemap.c: unconditionally call mark_page

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Date:	Thu, 15 Mar 2007 17:29:44 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	Chuck Ebbert <cebbert@...hat.com>
Cc:	Ashif Harji <asharji@...uwaterloo.ca>, linux-mm@...ck.org,
	Jan Kara <jack@...e.cz>, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org
Subject: Re: [PATCH] mm/filemap.c: unconditionally call mark_page_accessed

On Thu, Mar 15, 2007 at 11:56:59AM -0400, Chuck Ebbert wrote:
> Ashif Harji wrote:
> > 
> > This patch unconditionally calls mark_page_accessed to prevent pages,
> > especially for small files, from being evicted from the page cache
> > despite frequent access.
> > 
> > Signed-off-by: Ashif Harji <asharji@...a.uwaterloo.ca>
> > 
> 
> I like mine better -- it leaves the comment:

How about this? It also doesn't break the use-once heuristic.

--
A change to make database style random read() workloads perform better, by
calling mark_page_accessed for some non-page-aligned reads broke the case of
< PAGE_CACHE_SIZE files, which will not get their prev_index moved past the
first page.

Combine both heuristics for marking the page accessed.

Signed-off-by: Nick Piggin <npiggin@...e.de>

Index: linux-2.6/mm/filemap.c
===================================================================
--- linux-2.6.orig/mm/filemap.c
+++ linux-2.6/mm/filemap.c
@@ -929,7 +929,7 @@ page_ok:
 		 * When (part of) the same page is read multiple times
 		 * in succession, only mark it as accessed the first time.
 		 */
-		if (prev_index != index)
+		if (prev_index != index || !offset)
 			mark_page_accessed(page);
 		prev_index = index;
 
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