Re: 2.4 fix for write throttling on x86 >1G

Andrea Arcangeli
2005-03-11T20:56:21Z

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.