linux-kernel - Re: [PATCH] mm: fix page_mkclean_one (was: 2.6.19 file content corruption on ext3)

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Message-Id: <1166655553.9726.9.camel@kleikamp.austin.ibm.com>
Date:	Wed, 20 Dec 2006 16:59:13 -0600
From:	Dave Kleikamp <shaggy@...ux.vnet.ibm.com>
To:	Linus Torvalds <torvalds@...l.org>
Cc:	Martin Michlmayr <tbm@...ius.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Hugh Dickins <hugh@...itas.com>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Arjan van de Ven <arjan@...radead.org>,
	Andrei Popa <andrei.popa@...eo.ro>,
	Andrew Morton <akpm@...l.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Florian Weimer <fw@...eb.enyo.de>,
	Marc Haber <mh+linux-kernel@...schlus.de>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Arnd Bergmann <arnd.bergmann@...ibm.com>,
	gordonfarquharson@...il.com
Subject: Re: [PATCH] mm: fix page_mkclean_one (was: 2.6.19 file content
	corruption on ext3)

On Wed, 2006-12-20 at 14:25 -0800, Linus Torvalds wrote:
> 
> On Wed, 20 Dec 2006, Dave Kleikamp wrote:
> >
> > This patch removes some questionable code that attempted to make a
> > no-longer-used page easier to reclaim.
> 
> If so, "cancel_dirty_page()" may actually be the right thing to use, but
> only if you can guarantee that the page isn't mapped anywhere (and from
> the name of the function I guess it's not something that you'll ever map?)

That's correct.  It can't be mapped.  It's a private mapping only used
for metadata.

I'm really not sure the code in question is having the intended effect.
Maybe one of the gurus on cc: can take a look at the code and tell me if
it's worth keeping.  I apologize in advance if it makes anyone lose
their lunch.

> So the JFS code _looks_ like you could just replace the
> 
> 	clear_page_dirty(page);
> 
> with
> 
> 	cancel_dirty_page(page, PAGE_CACHE_SIZE);
> 
> (where that second parameter is just used for statistics - it updates the
> "cancelled IO" byte-counts if CONFIG_TASK_IO_ACCOUNTING is set - so the
> number doesn't really matter, you could make it zero if you never want the
> thing to show up in the IO accounting).

I'm not sure whether zero or PAGE_CACHE_SIZE would be better.  The
situation is where some page of metadata is no longer used, say
shrinking a directory tree or truncating a file and throwing out the
extent tree.

Thanks,
Shaggy
-- 
David Kleikamp
IBM Linux Technology Center

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