Re: [PATCH 14/14] fs,xfs: Allow kswapd to writeback pages

From: Mel Gorman
Date: Tue Jun 29 2010 - 08:52:13 EST

On Tue, Jun 29, 2010 at 08:37:22AM -0400, Christoph Hellwig wrote:
> I don't see a patch in this set which refuses writeback from the memcg
> context, which we identified as having large stack footprint in hte
> discussion of the last patch set.

It wasn't clear to me what the right approach was there and should
have noted that in the intro. The last note I have on it is this message which might
avoid the deep stack usage but I wasn't 100% sure. As kswapd doesn't clean
pages for memcg, I left memcg being able to direct writeback to see what
the memcg people preferred.

> Meanwhile I've submitted a patch to xfs to allow reclaim from kswapd,
> and just prevent it from direct and memcg reclaim.

Good stuff.

> Btw, it might be worth to also allow kswap to all writeout on ext4,
> but doing that will be a bit more complicated than the btrfs and xfs
> variants as the code is rather convoluted.

Fully agreed. I looked into it and got caught in its twisty web so
postponed it until this much can be finalised, agreed upon or rejected -
all pre-requisities to making the ext4 work worthwhile.

Mel Gorman
Part-time Phd Student Linux Technology Center
University of Limerick IBM Dublin Software Lab
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