linux-kernel - Re: [PATCH 0/8] readahead stats/tracing, backwards prefetching and more

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Message-ID: <20111121120027.GD8895@localhost>
Date:	Mon, 21 Nov 2011 20:00:27 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>
Subject: Re: [PATCH 0/8] readahead stats/tracing, backwards prefetching and
 more

On Mon, Nov 21, 2011 at 05:56:38PM +0800, Christoph Hellwig wrote:
> On Mon, Nov 21, 2011 at 05:18:19PM +0800, Wu Fengguang wrote:
> > Andrew,
> > 
> > I'm getting around to pick up the readahead works again :-)
> > 
> > This first series is mainly to add some debug facilities, to support the long
> > missed backwards prefetching capability, and some old patches that somehow get
> > delayed (shame me).
> > 
> > The next step would be to better handle the readahead thrashing situations.
> > That would require rewriting part of the algorithms, this is why I'd like to
> > keep the backwards prefetching simple and stupid for now.
> > 
> > When (almost) free of readahead thrashing, we'll be in a good position to lift
> > the default readahead size. Which I suspect would be the single most efficient
> > way to improve performance for the large volumes of casually maintained Linux
> > file servers.
> 
> Btw, if you work actively in that area I have a todo list item I was
> planning to look into sooner or later:  instead of embedding the ra
> state into the struct file allocate it dynamically.  That way files that
> either don't use the pagecache, or aren't read from won't need have to
> pay the price for increasing struct file size, and if we have to we
> could enlarge it more easily.

Agreed. That's good to have, please allow me to move it into my todo list :)

> Besides removing f_version in the common
> struct file and also allocting f_owner separately that seem to be the
> easiest ways to get struct file size down.

Yeah, there seems no much code accessing fown_struct.
I may consider that when I'm at file_ra_state, but no promise ;)

Thanks,
Fengguang
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