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Date: Fri, 27 May 2011 11:39:07 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Daisuke Nishimura <nishimura@....nes.nec.co.jp>,
Ying Han <yinghan@...gle.com>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>
Subject: Re: [PATCHv4] memcg: reclaim memory from node in round-robin
On Fri, 27 May 2011 08:54:40 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> On Thu, 26 May 2011 12:52:07 -0700
> Andrew Morton <akpm@...ux-foundation.org> wrote:
>
> > On Fri, 6 May 2011 15:13:02 +0900
> > KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> wrote:
> >
> > > > It would be much better to work out the optimum time at which to rotate
> > > > the index via some deterministic means.
> > > >
> > > > If we can't think of a way of doing that then we should at least pace
> > > > the rotation frequency via something saner than wall-time. Such as
> > > > number-of-pages-scanned.
> > > >
> > >
> > >
> > > What I think now is using reclaim_stat or usigng some fairness based on
> > > the ratio of inactive file caches. We can calculate the total sum of
> > > recalaim_stat which gives us a scan_ratio for a whole memcg. And we can
> > > calculate LRU rotate/scan ratio per node. If rotate/scan ratio is small,
> > > it will be a good candidate of reclaim target. Hmm,
> > >
> > > - check which memory(anon or file) should be scanned.
> > > (If file is too small, rotate/scan ratio of file is meaningless.)
> > > - check rotate/scan ratio of each nodes.
> > > - calculate weights for each nodes (by some logic ?)
> > > - give a fair scan w.r.t node's weight.
> > >
> > > Hmm, I'll have a study on this.
> >
> > How's the study coming along ;)
> >
> > I'll send this in to Linus today, but I'll feel grumpy while doing so.
> > We really should do something smarter here - the magic constant will
> > basically always be suboptimal for everyone and we end up tweaking its
> > value (if we don't, then the feature just wasn't valuable in the first
> > place) and then we add a tunable and then people try to tweak the
> > default setting of the tunable and then I deride them for not setting
> > the tunable in initscripts and then we have to maintain the stupid
> > tunable after we've changed the internal implementation and it's all
> > basically screwed up.
> >
> > How to we automatically determine the optimum time at which to rotate,
> > at runtime?
> >
>
> Ah, I think I should check it after dirty page accounting comes...because
> ratio of dirty pages is an important information..
>
> Ok, what I think now is just comparing the number of INACTIVE_FILE or the number
> of FILE CACHES per node.
>
> I think we can periodically update per-node and total amount of file caches
> and we can record per-node
> node-file-cache * 100/ total-file cache
> information into memcg's per-node structure.
>
Hmmm..something like this ?
==
This will not be able to be applied mmotm directly.
This patch is made from tons of magic numbers....I need more study
and will be able to write a simple one.
At first, mem_cgroup can reclaim memory from anywhere, it just checks
amount of memory. Now, victim node to be reclaimed is just determined
by round-robin.
This patch adds a scheduler simliar to a weighted fair share scanning
among nodes. Now, we periodically update mem->scan_nodes to know
which node has evictable memory. This patch gathers more information.
This patch caluculate "weight" of node as
(nr_inactive_file + nr_active_file/10) * (200-swappiness)
+ (nr_inactive_anon) * (swappiness)
(see vmscan.c::get_scan_count() for meaning of swappiness)
And select some nodes in a fair way proportional to the weight.
selected nodes are cached into mem->victim_nodes, victime_nodes
will be visited in round robin.
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
---
mm/memcontrol.c | 102 ++++++++++++++++++++++++++++++++++++++++++++++----------
1 file changed, 84 insertions(+), 18 deletions(-)
Index: memcg_async/mm/memcontrol.c
===================================================================
--- memcg_async.orig/mm/memcontrol.c
+++ memcg_async/mm/memcontrol.c
@@ -48,6 +48,7 @@
#include <linux/page_cgroup.h>
#include <linux/cpu.h>
#include <linux/oom.h>
+#include <linux/random.h>
#include "internal.h"
#include <asm/uaccess.h>
@@ -149,6 +150,7 @@ struct mem_cgroup_per_zone {
#define MEM_CGROUP_ZSTAT(mz, idx) ((mz)->count[(idx)])
struct mem_cgroup_per_node {
+ u64 scan_weight;
struct mem_cgroup_per_zone zoneinfo[MAX_NR_ZONES];
};
@@ -257,6 +259,7 @@ struct mem_cgroup {
int last_scanned_node;
#if MAX_NUMNODES > 1
nodemask_t scan_nodes;
+ nodemask_t victim_nodes;
unsigned long next_scan_node_update;
#endif
/*
@@ -1732,9 +1735,21 @@ u64 mem_cgroup_get_limit(struct mem_cgro
* nodes based on the zonelist. So update the list loosely once per 10 secs.
*
*/
+
+/*
+ * This is for selecting a victim node with lottery proportional share
+ * scheduling. This LOTTEY value can be arbitrary but must be higher
+ * than max number of nodes.
+ */
+#define NODE_SCAN_LOTTERY (1 << 15)
+#define NODE_SCAN_LOTTERY_MASK (NODE_SCAN_LOTTERY - 1)
+
static void mem_cgroup_may_update_nodemask(struct mem_cgroup *mem, bool force)
{
int nid;
+ u64 total_weight;
+ unsigned long swappiness;
+ int nr_selection;
if (!force && time_after(mem->next_scan_node_update, jiffies))
return;
@@ -1742,18 +1757,77 @@ static void mem_cgroup_may_update_nodema
mem->next_scan_node_update = jiffies + 10*HZ;
/* make a nodemask where this memcg uses memory from */
mem->scan_nodes = node_states[N_HIGH_MEMORY];
+ nodes_clear(mem->victim_nodes);
+
+ swappiness = mem_cgroup_swappiness(mem);
+ total_weight = 0;
for_each_node_mask(nid, node_states[N_HIGH_MEMORY]) {
+ u64 val, file_weight, anon_weight, pages;
+ int lru;
- if (mem_cgroup_get_zonestat_node(mem, nid, LRU_INACTIVE_FILE) ||
- mem_cgroup_get_zonestat_node(mem, nid, LRU_ACTIVE_FILE))
- continue;
+ lru = LRU_INACTIVE_FILE;
+ val = mem_cgroup_get_zonestat_node(mem, nid, lru);
+ file_weight = val;
+ pages = val;
- if (total_swap_pages &&
- (mem_cgroup_get_zonestat_node(mem, nid, LRU_INACTIVE_ANON) ||
- mem_cgroup_get_zonestat_node(mem, nid, LRU_ACTIVE_ANON)))
- continue;
- node_clear(nid, mem->scan_nodes);
+ lru = LRU_ACTIVE_FILE;
+ val = mem_cgroup_get_zonestat_node(mem, nid, lru);
+ /*
+ * This is a magic calculation. We add 10% of active file
+ * to weight. This should be tweaked..
+ */
+ if (val)
+ file_weight += val/10;
+ pages += val;
+
+ if (total_swap_pages) {
+ lru = LRU_INACTIVE_ANON;
+ val = mem_cgroup_get_zonestat_node(mem, nid, lru);
+ anon_weight = val;
+ pages += val;
+ lru = LRU_ACTIVE_ANON;
+ val = mem_cgroup_get_zonestat_node(mem, nid, lru);
+ /*
+ * Magic again. We don't want to active_anon take into
+ * account but cannot ignore....add +1.
+ */
+ if (val)
+ anon_weight += 1;
+ pages += val;
+ } else
+ anon_weight = 0;
+ mem->info.nodeinfo[nid]->scan_weight =
+ file_weight * (200 - swappiness) +
+ anon_weight * swappiness;
+ if (!pages)
+ node_clear(nid, mem->scan_nodes);
+
+ total_weight += mem->info.nodeinfo[nid]->scan_weight;
+ }
+ /* NORMALIZE weight information.*/
+ for_each_node_mask(nid, node_states[N_HIGH_MEMORY]) {
+
+ mem->info.nodeinfo[nid]->scan_weight =
+ mem->info.nodeinfo[nid]->scan_weight
+ * NODE_SCAN_LOTTERY/ total_weight;
+ }
+ /*
+ * because checking lottery at every scan is heavy. we cache
+ * some results. These victims will be used for the next 10sec.
+ * Even if scan_nodes is empty, the victim_nodes includes node 0
+ * at least.
+ */
+ nr_selection = int_sqrt(nodes_weight(mem->scan_nodes)) + 1;
+
+ while (nr_selection >= 0) {
+ int lottery = random32();
+ for_each_node_mask(nid, mem->scan_nodes) {
+ lottery -= mem->info.nodeinfo[nid]->scan_weight;
+ if (lottery <= 0)
+ break;
+ }
+ node_set(nid, mem->victim_nodes);
}
}
@@ -1776,17 +1850,9 @@ int mem_cgroup_select_victim_node(struct
mem_cgroup_may_update_nodemask(mem, false);
node = mem->last_scanned_node;
- node = next_node(node, mem->scan_nodes);
+ node = next_node(node, mem->victim_nodes);
if (node == MAX_NUMNODES)
- node = first_node(mem->scan_nodes);
- /*
- * We call this when we hit limit, not when pages are added to LRU.
- * No LRU may hold pages because all pages are UNEVICTABLE or
- * memcg is too small and all pages are not on LRU. In that case,
- * we use curret node.
- */
- if (unlikely(node == MAX_NUMNODES))
- node = numa_node_id();
+ node = first_node(mem->victim_nodes);
mem->last_scanned_node = node;
return node;
--
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