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Date: Mon, 3 Jun 2013 11:01:54 -0400
From: Johannes Weiner <hannes@...xchg.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: linux-mm@...ck.org, Andi Kleen <andi@...stfloor.org>,
Andrea Arcangeli <aarcange@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Greg Thelen <gthelen@...gle.com>,
Christoph Hellwig <hch@...radead.org>,
Hugh Dickins <hughd@...gle.com>, Jan Kara <jack@...e.cz>,
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
Mel Gorman <mgorman@...e.de>,
Minchan Kim <minchan.kim@...il.com>,
Rik van Riel <riel@...hat.com>,
Michel Lespinasse <walken@...gle.com>,
Seth Jennings <sjenning@...ux.vnet.ibm.com>,
Roman Gushchin <klamm@...dex-team.ru>,
metin d <metdos@...oo.com>, linux-kernel@...r.kernel.org,
linux-fsdevel@...r.kernel.org
Subject: Re: [patch 10/10] mm: workingset: keep shadow entries in check
On Mon, Jun 03, 2013 at 10:22:09AM +0200, Peter Zijlstra wrote:
> On Thu, May 30, 2013 at 02:04:06PM -0400, Johannes Weiner wrote:
> > 2. a list of files that contain shadow entries is maintained. If the
> > global number of shadows exceeds a certain threshold, a shrinker is
> > activated that reclaims old entries from the mappings. This is
> > heavy-handed but it should not be a common case and is only there
> > to protect from accidentally/maliciously induced OOM kills.
>
> Grrr.. another global files list. We've been trying rather hard to get
> rid of the first one :/
>
> I see why you want it but ugh.
I'll try to make it per-SB like the inode list. It probably won't be
per-SB shrinkers because of the global nature of the shadow limit, but
at least per-SB inode lists should be doable.
> I have similar worries for your global time counter, large machines
> might thrash on that one cacheline.
Fair enough.
So I'm trying the following idea: instead of the global time counter,
have per-zone time counters and store the zone along with those local
timestamps in the shadow entries (nid | zid | time). On refault, we
can calculate the zone-local distance first and then use the inverse
of the zone's eviction proportion to scale it to a global distance.
Delta for 9/10:
---
include/linux/mmzone.h | 1 +
mm/workingset.c | 74 ++++++++++++++++++++++++++++++--------------------
2 files changed, 46 insertions(+), 29 deletions(-)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 505bd80..24e9805 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -206,6 +206,7 @@ struct zone_reclaim_stat {
struct lruvec {
struct list_head lists[NR_LRU_LISTS];
struct zone_reclaim_stat reclaim_stat;
+ atomic_long_t workingset_time;
struct prop_local_percpu evictions;
long shrink_active;
#ifdef CONFIG_MEMCG
diff --git a/mm/workingset.c b/mm/workingset.c
index 7986aa4..5fd7277 100644
--- a/mm/workingset.c
+++ b/mm/workingset.c
@@ -85,27 +85,10 @@
*/
/*
- * Monotonic workingset clock for non-resident pages.
- *
- * The refault distance of a page is the number of ticks that occurred
- * between that page's eviction and subsequent refault.
- *
- * Every page slot that is taken away from the inactive list is one
- * more slot the inactive list would have to grow again in order to
- * hold the current non-resident pages in memory as well.
- *
- * As the refault distance needs to reflect the space missing on the
- * inactive list, the workingset time is advanced every time the
- * inactive list is shrunk. This means eviction, but also activation.
- */
-static atomic_long_t workingset_time;
-
-/*
* Workingset clock snapshots are stored in the page cache radix tree
* as exceptional entries (shadows).
*/
#define EV_SHIFT RADIX_TREE_EXCEPTIONAL_SHIFT
-#define EV_MASK (~0UL >> EV_SHIFT)
/*
* Per-zone proportional eviction counter to keep track of recent zone
@@ -115,12 +98,12 @@ static struct prop_descriptor global_evictions;
void *workingset_eviction(struct address_space *mapping, struct page *page)
{
+ struct zone *zone = page_zone(page);
struct lruvec *lruvec;
unsigned long time;
- time = atomic_long_inc_return(&workingset_time);
-
- lruvec = mem_cgroup_zone_lruvec(page_zone(page), NULL);
+ lruvec = mem_cgroup_zone_lruvec(zone, NULL);
+ time = atomic_long_inc_return(&lruvec->workingset_time);
prop_inc_percpu(&global_evictions, &lruvec->evictions);
/*
@@ -132,21 +115,57 @@ void *workingset_eviction(struct address_space *mapping, struct page *page)
if (mapping_exiting(mapping))
return NULL;
+ time = (time << NODES_SHIFT) | zone->node;
+ time = (time << ZONES_SHIFT) | zone_idx(zone);
+
return (void *)((time << EV_SHIFT) | RADIX_TREE_EXCEPTIONAL_ENTRY);
}
-unsigned long workingset_refault_distance(struct page *page)
+static void lruvec_refault_distance(unsigned long shadow,
+ struct lruvec **lruvec,
+ unsigned long *distance)
{
unsigned long time_of_eviction;
+ struct zone *zone;
unsigned long now;
+ int zid, nid;
+
+ shadow >>= EV_SHIFT;
+ zid = shadow & ((1UL << ZONES_SHIFT) - 1);
+ shadow >>= ZONES_SHIFT;
+ nid = shadow & ((1UL << NODES_SHIFT) - 1);
+ shadow >>= NODES_SHIFT;
+ time_of_eviction = shadow;
+ zone = NODE_DATA(nid)->node_zones + zid;
+
+ *lruvec = mem_cgroup_zone_lruvec(zone, NULL);
+
+ now = atomic_long_read(&(*lruvec)->workingset_time);
+
+ *distance = (now - time_of_eviction) &
+ (~0UL >> (EV_SHIFT + ZONES_SHIFT + NODES_SHIFT));
+}
+
+unsigned long workingset_refault_distance(struct page *page)
+{
+ unsigned long refault_distance;
+ unsigned long lruvec_distance;
+ struct lruvec *lruvec;
+ long denominator;
+ long numerator;
if (!page)
return ~0UL;
BUG_ON(!radix_tree_exceptional_entry(page));
- time_of_eviction = (unsigned long)page >> EV_SHIFT;
- now = atomic_long_read(&workingset_time);
- return (now - time_of_eviction) & EV_MASK;
+ lruvec_refault_distance((unsigned long)page,
+ &lruvec, &lruvec_distance);
+ prop_fraction_percpu(&global_evictions, &lruvec->evictions,
+ &numerator, &denominator);
+ if (!numerator)
+ numerator = 1;
+ refault_distance = mult_frac(lruvec_distance, denominator, numerator);
+ return refault_distance;
}
EXPORT_SYMBOL(workingset_refault_distance);
@@ -187,8 +206,7 @@ void workingset_zone_balance(struct zone *zone, unsigned long refault_distance)
*/
prop_fraction_percpu(&global_evictions, &lruvec->evictions,
&numerator, &denominator);
- missing = refault_distance * numerator;
- do_div(missing, denominator);
+ missing = mult_frac(refault_distance, numerator, denominator);
/*
* Protected pages should be challenged when the refault
@@ -207,9 +225,6 @@ void workingset_zone_balance(struct zone *zone, unsigned long refault_distance)
void workingset_activation(struct page *page)
{
struct lruvec *lruvec;
-
- atomic_long_inc(&workingset_time);
-
/*
* The lists are rebalanced when the inactive list is observed
* to be too small for activations. An activation means that
@@ -217,6 +232,7 @@ void workingset_activation(struct page *page)
* page, so back off further deactivation.
*/
lruvec = mem_cgroup_zone_lruvec(page_zone(page), NULL);
+ atomic_long_inc(&lruvec->workingset_time);
if (lruvec->shrink_active > 0)
lruvec->shrink_active--;
}
--
1.8.2.3
--
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