linux-kernel - Re: [RFC 5/5] Memory controller soft limit reclaim on contention

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Date:	Mon, 30 Jun 2008 16:56:34 +0900
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	balbir@...ux.vnet.ibm.com
Cc:	kosaki.motohiro@...fujitsu.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	YAMAMOTO Takashi <yamamoto@...inux.co.jp>,
	Paul Menage <menage@...gle.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [RFC 5/5] Memory controller soft limit reclaim on contention

> >>  #endif /* _LINUX_MEMCONTROL_H */
> >> diff -puN mm/vmscan.c~memory-controller-soft-limit-reclaim-on-contention mm/vmscan.c
> >> diff -puN mm/page_alloc.c~memory-controller-soft-limit-reclaim-on-contention mm/page_alloc.c
> >> --- linux-2.6.26-rc5/mm/page_alloc.c~memory-controller-soft-limit-reclaim-on-contention	2008-06-27 20:43:10.000000000 +0530
> >> +++ linux-2.6.26-rc5-balbir/mm/page_alloc.c	2008-06-27 20:43:10.000000000 +0530
> >> @@ -1669,7 +1669,14 @@ nofail_alloc:
> >>  	reclaim_state.reclaimed_slab = 0;
> >>  	p->reclaim_state = &reclaim_state;
> >>  
> >> -	did_some_progress = try_to_free_pages(zonelist, order, gfp_mask);
> >> +	/*
> >> +	 * First try to reclaim from memory control groups that have
> >> +	 * exceeded their soft limit
> >> +	 */
> >> +	did_some_progress = mem_cgroup_reclaim_on_contention(gfp_mask);
> >> +	if (!did_some_progress)
> >> +		did_some_progress = try_to_free_pages(zonelist, order,
> >> +							gfp_mask);
> > 
> > try_to_free_mem_cgroup_pages() assume memcg need only one page.
> > but this code break it.
> > 
> > if anyone need several continuous memory, mem_cgroup_reclaim_on_contention() reclaim 
> > one or a very few page and return >0, then cause page allocation failure.
> > 
> > shouldn't we extend try_to_free_mem_cgroup_pages() agruments?
> > 
> > 
> > in addition, if we don't assume try_to_free_mem_cgroup_pages() need one page,
> > we should implement lumpy reclaim to mem_cgroup_isolate_pages().
> > otherwise, cpu wasting significant increase.
> 
> The memory controller currently controls just *user* pages, which are all of
> order 1. Since pages are faulted in at different times, lumpy reclaim was not
> the highest priority for the memory controller. NOTE: the pages are duplicated
> on the per-zone LRU, so lumpy reclaim from there should work just fine.

yes, memcg used only one page.
but mem_cgroup_reclaim_on_contention() reclaim for generic alloc_pages(), instead for memcg.
we can't assume memcg usage.
isn't it?




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