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Date: Thu, 18 Aug 2011 09:17:50 +0900
From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To: Michal Hocko <mhocko@...e.cz>
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>,
"hannes@...xchg.org" <hannes@...xchg.org>,
"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>
Subject: Re: [PATCH v5 4/6] memg: calculate numa weight for vmscan
On Wed, 17 Aug 2011 16:34:18 +0200
Michal Hocko <mhocko@...e.cz> wrote:
> Sorry it took so long but I was quite busy recently.
>
> On Tue 09-08-11 19:11:00, KAMEZAWA Hiroyuki wrote:
> > caclculate node scan weight.
> >
> > Now, memory cgroup selects a scan target node in round-robin.
> > It's not very good...there is not scheduling based on page usages.
> >
> > This patch is for calculating each node's weight for scanning.
> > If weight of a node is high, the node is worth to be scanned.
> >
> > The weight is now calucauted on following concept.
> >
> > - make use of swappiness.
> > - If inactive-file is enough, ignore active-file
> > - If file is enough (w.r.t swappiness), ignore anon
> > - make use of recent_scan/rotated reclaim stats.
>
> The concept looks good (see the specific comments bellow). I would
> appreciate if the description was more descriptive (especially in the
> reclaim statistics part with the reasoning why it is better).
>
> > Then, a node contains many inactive file pages will be a 1st victim.
> > Node selection logic based on this weight will be in the next patch.
> >
> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> > ---
> > mm/memcontrol.c | 110 +++++++++++++++++++++++++++++++++++++++++++++++++++++---
> > 1 file changed, 105 insertions(+), 5 deletions(-)
> >
> > Index: mmotm-Aug3/mm/memcontrol.c
> > ===================================================================
> > --- mmotm-Aug3.orig/mm/memcontrol.c
> > +++ mmotm-Aug3/mm/memcontrol.c
> [...]
> > @@ -1568,18 +1570,108 @@ static bool test_mem_cgroup_node_reclaim
> > }
> > #if MAX_NUMNODES > 1
> >
> > +static unsigned long
> > +__mem_cgroup_calc_numascan_weight(struct mem_cgroup * memcg,
> > + int nid,
> > + unsigned long anon_prio,
> > + unsigned long file_prio,
> > + int lru_mask)
> > +{
> > + u64 file, anon;
> > + unsigned long weight, mask;
>
> mask is not used anywhere.
>
I'll remove this.
> > + unsigned long rotated[2], scanned[2];
> > + int zid;
> > +
> > + scanned[0] = 0;
> > + scanned[1] = 0;
> > + rotated[0] = 0;
> > + rotated[1] = 0;
> > +
> > + for (zid = 0; zid < MAX_NR_ZONES; zid++) {
> > + struct mem_cgroup_per_zone *mz;
> > +
> > + mz = mem_cgroup_zoneinfo(memcg, nid, zid);
> > + scanned[0] += mz->reclaim_stat.recent_scanned[0];
> > + scanned[1] += mz->reclaim_stat.recent_scanned[1];
> > + rotated[0] += mz->reclaim_stat.recent_rotated[0];
> > + rotated[1] += mz->reclaim_stat.recent_rotated[1];
> > + }
> > + file = mem_cgroup_node_nr_lru_pages(memcg, nid, lru_mask & LRU_ALL_FILE);
> > +
> > + if (total_swap_pages)
>
> What about ((lru_mask & LRU_ALL_ANON) && total_swap_pages)?
Ok. will add that.
> Why should we go down the mem_cgroup_node_nr_lru_pages if are not getting anything?
>
> > + anon = mem_cgroup_node_nr_lru_pages(memcg,
> > + nid, mask & LRU_ALL_ANON);
>
> btw. s/mask/lru_mask/
>
yes...
> > + else
> > + anon = 0;
>
> Can be initialized during declaration (makes patch smaller).
>
Sure.
> > + if (!(file + anon))
> > + node_clear(nid, memcg->scan_nodes);
>
> In that case we can return with 0 right away.
>
yes.
> > +
> > + /* 'scanned - rotated/scanned' means ratio of finding not active. */
> > + anon = anon * (scanned[0] - rotated[0]) / (scanned[0] + 1);
> > + file = file * (scanned[1] - rotated[1]) / (scanned[1] + 1);
>
> OK, makes sense. We should not reclaim from nodes that are known to be
> hard to reclaim from. We, however, have to be careful to not exclude the
> node from reclaiming completely.
>
> > +
> > + weight = (anon * anon_prio + file * file_prio) / 200;
>
> Shouldn't we rather normalize the weight to the node size? This way we
> are punishing bigger nodes, aren't we.
>
Here, the routine is for reclaiming memory in a memcg in smooth way.
And not for balancing zone. It will be kswapd+memcg(softlimit) work.
The size of node in this memcg is represented by file + anon.
> > + return weight;
> > +}
> > +
> > +/*
> > + * Calculate each NUMA node's scan weight. scan weight is determined by
> > + * amount of pages and recent scan ratio, swappiness.
> > + */
> > +static unsigned long
> > +mem_cgroup_calc_numascan_weight(struct mem_cgroup *memcg)
> > +{
> > + unsigned long weight, total_weight;
> > + u64 anon_prio, file_prio, nr_anon, nr_file;
> > + int lru_mask;
> > + int nid;
> > +
> > + anon_prio = mem_cgroup_swappiness(memcg) + 1;
> > + file_prio = 200 - anon_prio + 1;
>
> What is +1 good for. I do not see that anon_prio would be used as a
> denominator.
>
weight = (anon * anon_prio + file * file_prio) / 200;
Just for avoiding the influence of anon never be 0 (by wrong value
set to swappiness by user.)
> > +
> > + lru_mask = BIT(LRU_INACTIVE_FILE);
> > + if (mem_cgroup_inactive_file_is_low(memcg))
> > + lru_mask |= BIT(LRU_ACTIVE_FILE);
> > + /*
> > + * In vmscan.c, we'll scan anonymous pages with regard to memcg/zone's
> > + * amounts of file/anon pages and swappiness and reclaim_stat. Here,
> > + * we try to find good node to be scanned. If the memcg contains enough
> > + * file caches, we'll ignore anon's weight.
> > + * (Note) scanning anon-only node tends to be waste of time.
> > + */
> > +
> > + nr_file = mem_cgroup_nr_lru_pages(memcg, LRU_ALL_FILE);
> > + nr_anon = mem_cgroup_nr_lru_pages(memcg, LRU_ALL_ANON);
> > +
> > + /* If file cache is small w.r.t swappiness, check anon page's weight */
> > + if (nr_file * file_prio >= nr_anon * anon_prio)
> > + lru_mask |= BIT(LRU_INACTIVE_ANON);
>
> Why we do not care about active anon (e.g. if inactive anon is low)?
>
This condition is wrong...
if (nr_file * file_prio <= nr_anon * anon_prio)
lru_mask |= BIT(LRU_INACTIVE_ANON);
I was worried about LRU_ACTIVE_ANON. I considered
- We can't handle ACTIVE_ANON and INACTIVE_ANON in the same weight.
But I don't want to add more magic numbers.
- vmscan.c:shrink_zone() scans ACTIVE_ANON whenever/only when
inactive_anon_is_low()==true. SWAP_CLUSTER_MAX per priority.
It's specially handled.
So, I thought involing the number of ACTIVE_ANON to the weight is difficult
and ignored ACTIVE_ANON, here. Do you have idea ?
> > +
> > + total_weight = 0;
>
> Can be initialized during declaration.
>
will fix.
Thanks,
-Kame
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