Re: [RFC PATCH 0/6] Do not call ->writepage[s] from direct reclaim and use a_ops->writepages() where possible

Christoph Hellwig
2010-06-11T16:29:15Z

On Tue, Jun 08, 2010 at 10:28:14AM +0100, Mel Gorman wrote:
> > - we also need to care about ->releasepage. At least for XFS it
> > can end up in the same deep allocator chain as ->writepage because
> > it does all the extent state conversions, even if it doesn't
> > start I/O.
>
> Dang.
>
> > I haven't managed yet to decode the ext4/btrfs codepaths
> > for ->releasepage yet to figure out how they release a page that
> > covers a delayed allocated or unwritten range.
> >
>
> If ext4/btrfs are also very deep call-chains and this series is going more
> or less the right direction, then avoiding calling ->releasepage from direct
> reclaim is one, somewhat unfortunate, option. The second is to avoid it on
> a per-filesystem basis for direct reclaim using PF_MEMALLOC to detect
> reclaimers and PF_KSWAPD to tell the difference between direct
> reclaimers and kswapd.

I went throught this a bit more and I can't actually hit that code in
XFS ->releasepage anymore. I've also audited the caller and can't see
how we could theoretically hit it anymore. Do the VM gurus know a case
where we would call ->releasepage on a page that's actually dirty and
hasn't been through block_invalidatepage before?