Re: [PATCH] vmscan: memcg needs may_swap (Re: [patch] vmscan: rename sc.may_swap to may_unmap)

[Johannes Weiner <hannes@cmpxchg.org>]

On Wed, Apr 01, 2009 at 06:55:45PM +0900, KOSAKI Motohiro wrote:
> > > > How about making may_swap mean the following:
> > > > 
> > > > 	@@ -642,6 +639,8 @@ static unsigned long shrink_page_list(st
> > > > 	 		 * Try to allocate it some swap space here.
> > > > 	 		 */
> > > > 	 		if (PageAnon(page) && !PageSwapCache(page)) {
> > > > 	+			if (!sc->map_swap)
> > > > 	+				goto keep_locked;
> > > > 	 			if (!(sc->gfp_mask & __GFP_IO))
> > > > 	 				goto keep_locked;
> > > > 	 			if (!add_to_swap(page))
> > > > 
> > > > try_to_free_pages() always sets it.
> > > > 
> > > What is the advantage than _not_ scanning ANON LRU at all ?
> > 
> > I thought we could collect anon pages that don't need swap io.
> 
> Yes. but Is this important?
> if memcg reclaim don't collect sleal swapcache, other global reclaim can.
> 
> Am I missing any viewpoint?

Nothing I am aware of, it should work as you suggest.  I just wasn't
sure about the memory controller.