summaryrefslogtreecommitdiffstats
diff options
context:
space:
mode:
authorCody P Schafer <cody@linux.vnet.ibm.com>2013-07-03 15:01:31 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2013-07-03 16:07:27 -0700
commit8d7a8fa97abeb4fd6b3975d32c9f859875157770 (patch)
tree99e057e6b90bd514e645ed0539d1d1b8178046d3
parentc8e251fadc6220261f6e0c6b8a4f1cdf27626165 (diff)
downloadlinux-8d7a8fa97abeb4fd6b3975d32c9f859875157770.tar.bz2
mm/page_alloc: insert memory barriers to allow async update of pcp batch and high
Introduce pageset_update() to perform a safe transision from one set of pcp->{batch,high} to a new set using memory barriers. This ensures that batch is always set to a safe value (1) prior to updating high, and ensure that high is fully updated before setting the real value of batch. It avoids ->batch ever rising above ->high. Suggested by Gilad Ben-Yossef in these threads: https://lkml.org/lkml/2013/4/9/23 https://lkml.org/lkml/2013/4/10/49 Also reproduces his proposed comment. Signed-off-by: Cody P Schafer <cody@linux.vnet.ibm.com> Reviewed-by: Gilad Ben-Yossef <gilad@benyossef.com> Cc: KOSAKI Motohiro <kosaki.motohiro@gmail.com> Cc: Mel Gorman <mgorman@suse.de> Cc: Pekka Enberg <penberg@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/page_alloc.c41
1 files changed, 32 insertions, 9 deletions
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 8d4335779633..eaaef2a09424 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4035,12 +4035,37 @@ static int __meminit zone_batchsize(struct zone *zone)
#endif
}
+/*
+ * pcp->high and pcp->batch values are related and dependent on one another:
+ * ->batch must never be higher then ->high.
+ * The following function updates them in a safe manner without read side
+ * locking.
+ *
+ * Any new users of pcp->batch and pcp->high should ensure they can cope with
+ * those fields changing asynchronously (acording the the above rule).
+ *
+ * mutex_is_locked(&pcp_batch_high_lock) required when calling this function
+ * outside of boot time (or some other assurance that no concurrent updaters
+ * exist).
+ */
+static void pageset_update(struct per_cpu_pages *pcp, unsigned long high,
+ unsigned long batch)
+{
+ /* start with a fail safe value for batch */
+ pcp->batch = 1;
+ smp_wmb();
+
+ /* Update high, then batch, in order */
+ pcp->high = high;
+ smp_wmb();
+
+ pcp->batch = batch;
+}
+
/* a companion to setup_pagelist_highmark() */
static void pageset_set_batch(struct per_cpu_pageset *p, unsigned long batch)
{
- struct per_cpu_pages *pcp = &p->pcp;
- pcp->high = 6 * batch;
- pcp->batch = max(1UL, 1 * batch);
+ pageset_update(&p->pcp, 6 * batch, max(1UL, 1 * batch));
}
static void setup_pageset(struct per_cpu_pageset *p, unsigned long batch)
@@ -4064,13 +4089,11 @@ static void setup_pageset(struct per_cpu_pageset *p, unsigned long batch)
static void setup_pagelist_highmark(struct per_cpu_pageset *p,
unsigned long high)
{
- struct per_cpu_pages *pcp;
+ unsigned long batch = max(1UL, high / 4);
+ if ((high / 4) > (PAGE_SHIFT * 8))
+ batch = PAGE_SHIFT * 8;
- pcp = &p->pcp;
- pcp->high = high;
- pcp->batch = max(1UL, high/4);
- if ((high/4) > (PAGE_SHIFT * 8))
- pcp->batch = PAGE_SHIFT * 8;
+ pageset_update(&p->pcp, high, batch);
}
static void __meminit setup_zone_pageset(struct zone *zone)