linux-kernel - Re: [PATCH 0/7] Kill PF

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Message-ID: <20091117124715.GA22834@infradead.org>
Date:	Tue, 17 Nov 2009 07:47:15 -0500
From:	Christoph Hellwig <hch@...radead.org>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 0/7] Kill PF_MEMALLOC abuse

On Tue, Nov 17, 2009 at 09:24:24PM +0900, KOSAKI Motohiro wrote:
> > On Tue, Nov 17, 2009 at 07:24:42PM +0900, KOSAKI Motohiro wrote:
> > > if xfsbufd doesn't only write out dirty data but also drop page,
> > > I agree you. 
> > 
> > It then drops the reference to the buffer which drops references to the
> > pages, which often are the last references, yes.
> 
> I though it is not typical case. Am I wrong?
> if so, I'm sorry. I'm not XFS expert.

I think in the typical case it's the last reference.  The are two
reasons why it might not be:

 - we're on a filesystem with block size < page size in which case two
   buffers can share a page and we'd need to write out and release both
   buffers to free the page
 - someone else might have a reference on the buffer.  Offhand I can't
   remember a place where we do this for delayed write buffers (which
   is what xfsbufd writes out) as it would be a bit against the purpose
   of those delayed write buffers.

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