Re: [patch 3/3] mm: keep pages from unevictable mappings off the LRU lists

[KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>]

> On Mon, Mar 23, 2009 at 11:21:36AM +0900, KOSAKI Motohiro wrote:
> > > Hmm,,
> > > 
> > > This patch is another thing unlike previous series patches.
> > > Firstly, It looked good to me.
> > > 
> > > I think add_to_page_cache_lru have to become a fast path.
> > > But, how often would ramfs and shmem function be called ?
> > > 
> > > I have a concern for this patch to add another burden.
> > > so, we need any numbers for getting pros and cons.
> > > 
> > > Any thoughts ?
> > 
> > this is the just reason why current code don't call add_page_to_unevictable_list().
> > add_page_to_unevictable_list() don't use pagevec. it is needed for avoiding race.
> > 
> > then, if readahead path (i.e. add_to_page_cache_lru()) use add_page_to_unevictable_list(),
> > it can cause zone->lru_lock contention storm.
> 
> How is it different then shrink_page_list()?  If readahead put a
> contiguous chunk of unevictable pages to the file lru, then
> shrink_page_list() will as well call add_page_to_unevictable_list() in
> a loop.

it's probability issue.

readahead: we need to concern
	(1) readahead vs readahead
	(2) readahead vs reclaim

vmscan: we need to concern
	(3) background reclaim vs foreground reclaim

So, (3) is rarely event than (1) and (2).
Am I missing anything?