Message-ID: <457FBDBE.10102@FreeBSD.org>
Date: Wed, 13 Dec 2006 00:45:50 -0800
From: Suleiman Souhlal <ssouhlal@FreeBSD.org>
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To: akpm@osdl.org
CC: linux-kernel@vger.kernel.org, balbir@in.ibm.com, csturtiv@sgi.com,
       daw@sgi.com, guillaume.thouvenin@bull.net, jlan@sgi.com,
       nagar@watson.ibm.com, tee@sgi.com
Subject: Re: [patch 03/13] io-accounting: write accounting
References: <200612081152.kB8BqQvb019756@shell0.pdx.osdl.net>
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akpm@osdl.org wrote:
> From: Andrew Morton <akpm@osdl.org>
> 
> Accounting writes is fairly simple: whenever a process flips a page from clean
> to dirty, we accuse it of having caused a write to underlying storage of
> PAGE_CACHE_SIZE bytes.

On architectures where dirtying a page doesn't cause a page fault (like i386), couldn't you end up billing the wrong process (in fact, I think that even on other archituctures set_page_dirty() doesn't get called immediately in the page fault handler)? 

AFAICS, set_page_dirty() is mostly called when trying to unmap a page when trying to shrink LRU lists, and there is no guarantee that this happens under the process that dirtied it (in fact, the set_page_dirty() is often done by kswapd).

-- Suleiman
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