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Date: Wed, 27 Apr 2011 13:28:14 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To: Ying Han <yinghan@...gle.com>
Cc: "linux-mm@...ck.org" <linux-mm@...ck.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
Daisuke Nishimura <nishmura@....nes.nec.co.jp>,
"kosaki.motohiro@...fujitsu.com" <kosaki.motohiro@...fujitsu.com>
Subject: Re: [PATCH] memcg: reclaim memory from nodes in round robin
On Tue, 26 Apr 2011 20:52:39 -0700
Ying Han <yinghan@...gle.com> wrote:
> On Tue, Apr 26, 2011 at 7:57 PM, KAMEZAWA Hiroyuki
> <kamezawa.hiroyu@...fujitsu.com> wrote:
> > Now, memory cgroup's direct reclaim frees memory from the current node.
> > But this has some troubles. In usual, when a set of threads works in
> > cooperative way, they are tend to on the same node. So, if they hit
> > limits under memcg, it will reclaim memory from themselves, it may be
> > active working set.
> >
> > For example, assume 2 node system which has Node 0 and Node 1
> > and a memcg which has 1G limit. After some work, file cacne remains and
> > and usages are
> > Node 0: 1M
> > Node 1: 998M.
> >
> > and run an application on Node 0, it will eats its foot before freeing
> > unnecessary file caches.
> >
> > This patch adds round-robin for NUMA and adds equal pressure to each
> > node. When using cpuset's spread memory feature, this will work very well.
> >
> > But yes, better algorithm is appreciated.
> >
> > From: Ying Han <yinghan@...gle.com>
> > Signed-off-by: Ying Han <yinghan@...gle.com>
> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> > ---
> > include/linux/memcontrol.h | 1 +
> > mm/memcontrol.c | 25 +++++++++++++++++++++++++
> > mm/vmscan.c | 9 ++++++++-
> > 3 files changed, 34 insertions(+), 1 deletion(-)
> >
> > Index: memcg/include/linux/memcontrol.h
> > ===================================================================
> > --- memcg.orig/include/linux/memcontrol.h
> > +++ memcg/include/linux/memcontrol.h
> > @@ -108,6 +108,7 @@ extern void mem_cgroup_end_migration(str
> > */
> > int mem_cgroup_inactive_anon_is_low(struct mem_cgroup *memcg);
> > int mem_cgroup_inactive_file_is_low(struct mem_cgroup *memcg);
> > +int mem_cgroup_select_victim_node(struct mem_cgroup *memcg);
> > unsigned long mem_cgroup_zone_nr_pages(struct mem_cgroup *memcg,
> > struct zone *zone,
> > enum lru_list lru);
> > Index: memcg/mm/memcontrol.c
> > ===================================================================
> > --- memcg.orig/mm/memcontrol.c
> > +++ memcg/mm/memcontrol.c
> > @@ -237,6 +237,7 @@ struct mem_cgroup {
> > * reclaimed from.
> > */
> > int last_scanned_child;
> > + int last_scanned_node;
> > /*
> > * Should the accounting and control be hierarchical, per subtree?
> > */
> > @@ -1472,6 +1473,29 @@ mem_cgroup_select_victim(struct mem_cgro
> > }
> >
> > /*
> > + * Selecting a node where we start reclaim from. Because what we need is just
> > + * reducing usage counter, start from anywhere is O,K. When considering
> > + * memory reclaim from current node, there are pros. and cons.
> > + * Freeing memory from current node means freeing memory from a node which
> > + * we'll use or we've used. So, it may make LRU bad. And if several threads
> > + * hit limits, it will see a contention on a node. But freeing from remote
> > + * node mean more costs for memory reclaim because of memory latency.
> > + *
> > + * Now, we use round-robin. Better algorithm is welcomed.
> > + */
> > +int mem_cgroup_select_victim_node(struct mem_cgroup *mem)
> > +{
> > + int node;
> > +
> > + node = next_node(mem->last_scanned_node, node_states[N_HIGH_MEMORY]);
> > + if (node == MAX_NUMNODES)
> > + node = first_node(node_states[N_HIGH_MEMORY]);
> > +
> > + mem->last_scanned_node = node;
> > + return node;
> > +}
> > +
> > +/*
> > * Scan the hierarchy if needed to reclaim memory. We remember the last child
> > * we reclaimed from, so that we don't end up penalizing one child extensively
> > * based on its position in the children list.
> > @@ -4678,6 +4702,7 @@ mem_cgroup_create(struct cgroup_subsys *
> > res_counter_init(&mem->memsw, NULL);
> > }
> > mem->last_scanned_child = 0;
> > + mem->last_scanned_node = MAX_NUMNODES;
> > INIT_LIST_HEAD(&mem->oom_notify);
> >
> > if (parent)
> > Index: memcg/mm/vmscan.c
> > ===================================================================
> > --- memcg.orig/mm/vmscan.c
> > +++ memcg/mm/vmscan.c
> > @@ -2198,6 +2198,7 @@ unsigned long try_to_free_mem_cgroup_pag
> > {
> > struct zonelist *zonelist;
> > unsigned long nr_reclaimed;
> > + int nid;
> > struct scan_control sc = {
> > .may_writepage = !laptop_mode,
> > .may_unmap = 1,
> > @@ -2208,10 +2209,16 @@ unsigned long try_to_free_mem_cgroup_pag
> > .mem_cgroup = mem_cont,
> > .nodemask = NULL, /* we don't care the placement */
> > };
> > + /*
> > + * Unlike direct reclaim via allo_pages(), memcg's reclaim
> > + * don't take care from where we get free resouce. So, the node where
> > + * we need to start scan is not need to be current node.
> > + */
> Sorry, some typos. alloc_pages() instead of alloc_pages(). And "free resource".
>
ok, will fix. Thank you for pointing out.
Thanks,
-Kame
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