linux-kernel - Re: RFC: CONFIG_PAGE_SHIFT (aka software PAGE

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Message-ID: <20070712144449.GZ31489@sgi.com>
Date:	Fri, 13 Jul 2007 00:44:49 +1000
From:	David Chinner <dgc@....com>
To:	Andrea Arcangeli <andrea@...e.de>
Cc:	David Chinner <dgc@....com>, linux-kernel@...r.kernel.org
Subject: Re: RFC: CONFIG_PAGE_SHIFT (aka software PAGE_SIZE)

On Thu, Jul 12, 2007 at 01:14:36PM +0200, Andrea Arcangeli wrote:
> On Thu, Jul 12, 2007 at 10:12:56AM +1000, David Chinner wrote:
> > I need really large filesystems that contain both small and large files to
> > work more efficiently on small boxes where we can't throw endless amounts of
> > RAM and CPUs at the problem.  Hence things like 64k page size are just not an
> > option because of the wastage that it entails.
> 
> I didn't know you were allocating 4k pages for the small files and 64k
> for the large ones in the same fs. That sounds quite a bit
> overkill.

We already have rudimentary multi-block size support via the
per-inode extent size hint, but we still cache based on the
filesystem block size ('coz we can't increase it).

All I want is to be able to change the index granularity in the page
cache with minimal impact and everything in XFS falls almost
straight out in a pretty optimal manner.

> I still think you should run those systems with PAGE_SIZE 64k even if
> it'll waste you more memory on the small files.

That's crap. Just because a machine has lots of memory does not
make it OK to waste lots of memory.

Cheers,

Dave.
-- 
Dave Chinner
Principal Engineer
SGI Australian Software Group
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