Re: [PATCH 4/8] vmscan: Do not writeback filesystem pages in direct reclaim

Mel Gorman
2010-07-19T14:26:40Z

On Mon, Jul 19, 2010 at 10:19:34AM -0400, Christoph Hellwig wrote:
> On Mon, Jul 19, 2010 at 02:11:26PM +0100, Mel Gorman wrote:
> > As the call-chain for writing anonymous pages is not expected to be deep
> > and they are not cleaned by flusher threads, anonymous pages are still
> > written back in direct reclaim.
>
> While it is not quite as deep as it skips the filesystem allocator and
> extent mapping code it can still be quite deep for swap given that it
> still has to traverse the whole I/O stack. Probably not worth worrying
> about now, but we need to keep an eye on it.
>

Agreed that we need to keep an eye on it. If this ever becomes a
problem, we're going to need to consider a flusher for anonymous pages.
If you look at the figures, we are still doing a lot of writeback of
anonymous pages. Granted, the layout of swap sucks anyway but it's
something to keep at the back of the mind.

> The patch looks fine to me anyway.
>

Thanks.

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