Date: Fri, 11 Mar 2005 21:53:09 +0100
From: Andrea Arcangeli <andrea@suse.de>
To: Marcelo Tosatti <marcelo.tosatti@cyclades.com>
Cc: linux-kernel@vger.kernel.org
Subject: Re: 2.4 fix for write throttling on x86 >1G
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References: <20050311061035.GZ26348@opteron.random> <20050311160413.GK4816@logos.cnet>
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Hello Marcelo,

On Fri, Mar 11, 2005 at 01:04:13PM -0300, Marcelo Tosatti wrote:
> Out of curiosity, that was SuSE not mainline ? 

yep.

> Do we really want to limit dirty cache to low mem on HIGHIO capable 
> machines? I'm afraid doing so might hurt performance on such systems.
> 
> I think it might be wise to have nr_free_buffer_pages() take highmem
> into account if CONFIG_HIGHIO is set ?

The problem is the buffercache/blkdev-pagecache: it simply can't go in
highmem. A similar fix happened recently in 2.6 for the same reasons,
but in 2.6 we allowed it with some logic specific for the
blkdev-pagecache.

nr_free_buffer_pages() was never intended to take highmem into account,
that's why there's the GFP_USER thing already, except we didn't loop
into the zonelist, so I didn't try to make a fix similar to 2.6.
-
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