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

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Date:	Thu, 15 Mar 2007 15:06:01 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Andrea Arcangeli <andrea@...e.de>
Cc:	Ashif Harji <asharji@...uwaterloo.ca>, dingxn@....ohio-state.edu,
	shaggy@...ux.vnet.ibm.com, andi@...x01.fht-esslingen.de,
	linux-mm@...ck.org, npiggin@...e.de, jack@...e.cz,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/filemap.c: unconditionally call mark_page_accessed

On Thu, 15 Mar 2007 22:49:23 +0100
Andrea Arcangeli <andrea@...e.de> wrote:

> On Thu, Mar 15, 2007 at 11:07:35AM -0800, Andrew Morton wrote:
> > > On Thu, 15 Mar 2007 01:22:45 -0400 (EDT) Ashif Harji <asharji@...uwaterloo.ca> wrote:
> > > I still think the simple fix of removing the 
> > > condition is the best approach, but I'm certainly open to alternatives.
> > 
> > Yes, the problem of falsely activating pages when the file is read in small
> > hunks is worse than the problem which your patch fixes.
> 
> Really? I would have expected all performance sensitive apps to read
> in >=PAGE_SIZE chunks. And if they don't because they split their
> dataset in blocks (like some database), it may not be so wrong to
> activate those pages that have two "hot" blocks more aggressively than
> those pages with a single hot block.

But the problem which is being fixed here is really obscure: an application
repeatedly reading the first page and only the first page of a file, always
via the same fd.

I'd expect that the sub-page-size read scenarion happens heaps more often
than that, especially when dealing with larger PAGE_SIZEs.


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