linux-kernel - Re: Status of buffered write path (deadlock fixes)

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Date:	Tue, 12 Dec 2006 20:47:38 -0500
From:	Trond Myklebust <trond.myklebust@....uio.no>
To:	Nick Piggin <nickpiggin@...oo.com.au>
Cc:	Mark Fasheh <mark.fasheh@...cle.com>,
	Linux Memory Management <linux-mm@...ck.org>,
	linux-fsdevel@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>,
	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	Andrew Morton <akpm@...gle.com>
Subject: Re: Status of buffered write path (deadlock fixes)

On Wed, 2006-12-13 at 11:53 +1100, Nick Piggin wrote:

> Not silly -- I guess that is the main sticking point. Luckily *most*
> !uptodate pages will be ones that we have newly allocated so will
> not be in pagecache yet.
> 
> If it is in pagecache, we could do one of a number of things: either
> remove it or try to bring it uptodate ourselves. I'm not yet sure if
> either of these actions will cause other problems, though :P
> 
> If both of those are really going to cause problems, then we could
> solve this in a more brute force way (assuming that !uptodate, locked
> pages, in pagecache at this point are very rare -- AFAIKS these will
> only be caused by IO errors?). We could allocate another, temporary
> page and copy the contents into there first, then into the target
> page after the prepare_write.

We are NOT going to mandate read-modify-write behaviour on
prepare_write()/commit_write(). That would be a completely unnecessary
slowdown for write-only workloads on NFS.

Trond

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