linux-kernel - Re: [PATCH RFC] extent mapped page cache

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Date:	Wed, 25 Jul 2007 04:32:17 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	Chris Mason <chris.mason@...cle.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Trond Myklebust <trond.myklebust@....uio.no>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH RFC] extent mapped page cache

On Tue, Jul 24, 2007 at 07:25:09PM -0400, Chris Mason wrote:
> On Tue, 24 Jul 2007 23:25:43 +0200
> Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
> 
> The tree is a critical part of the patch, but it is also the easiest to
> rip out and replace.  Basically the code stores a range by inserting
> an object at an index corresponding to the end of the range.
> 
> Then it does searches by looking forward from the start of the range.
> More or less any tree that can search and return the first key >=
> than the requested key will work.
> 
> So, I'd be happy to rip out the tree and replace with something else.
> Going completely lockless will be tricky, its something that will deep
> thought once the rest of the interface is sane.

Just having the other tree and managing it is what makes me a little
less positive of this approach, especially using it to store pagecache
state when we already have the pagecache tree.

Having another tree to store block state I think is a good idea as I
said in the fsblock thread with Dave, but I haven't clicked as to why
it is a big advantage to use it to manage pagecache state. (and I can
see some possible disadvantages in locking and tree manipulation overhead).

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