Re: [PATCH 5/5] mm: writeback: Prioritise dirty inodes encountered by direct reclaim for background flushing

[Christoph Hellwig <hch@xxxxxxxxxxxxx>]

On Wed, Jul 13, 2011 at 03:31:27PM +0100, Mel Gorman wrote:
> It is preferable that no dirty pages are dispatched from the page
> reclaim path. If reclaim is encountering dirty pages, it implies that
> either reclaim is getting ahead of writeback or use-once logic has
> prioritise pages for reclaiming that are young relative to when the
> inode was dirtied.

what does this buy us?  If at all we should prioritize by a zone,
e.g. tell write_cache_pages only to bother with writing things out
if the dirty page is in a given zone.   We'd probably still cluster
around it to make sure we get good I/O patterns, but would only start
I/O if it has a page we actually care about.