The patch titled
Subject: mm/page_alloc: factor out setting of pcp->high and pcp->batch
has been added to the -mm tree. Its filename is
mm-page_alloc-factor-out-setting-of-pcp-high-and-pcp-batch.patch
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From: Cody P Schafer <cody@xxxxxxxxxxxxxxxxxx>
Subject: mm/page_alloc: factor out setting of pcp->high and pcp->batch
"Problems" with the current code:
1: there is a lack of synchronization in setting ->high and ->batch in
percpu_pagelist_fraction_sysctl_handler()
2: stop_machine() in zone_pcp_update() is unnecissary.
3: zone_pcp_update() does not consider the case where
percpu_pagelist_fraction is non-zero
To fix:
1: add memory barriers, a safe ->batch value, an update side mutex when
updating ->high and ->batch, and use ACCESS_ONCE() for ->batch users
that expect a stable value.
2: avoid draining pages in zone_pcp_update(), rely upon the memory
barriers added to fix #1
3: factor out quite a few functions, and then call the appropriate one.
Note that it results in a change to the behavior of zone_pcp_update(),
which is used by memory_hotplug. I'm rather certain that I've diserned
(and preserved) the essential behavior (changing ->high and ->batch), and
only eliminated unneeded actions (draining the per cpu pages), but this
may not be the case.
Further note that the draining of pages that previously took place in
zone_pcp_update() occured after repeated draining when attempting to
offline a page, and after the offline has "succeeded". It appears that
the draining was added to zone_pcp_update() to avoid refactoring
setup_pageset() into 2 funtions.
This patch:
Creates pageset_set_batch() for use in setup_pageset().
pageset_set_batch() imitates the functionality of
setup_pagelist_highmark(), but uses the boot time
(percpu_pagelist_fraction == 0) calculations for determining ->high based
on ->batch.
Signed-off-by: Cody P Schafer <cody@xxxxxxxxxxxxxxxxxx>
Cc: Gilad Ben-Yossef <gilad@xxxxxxxxxxxxx>
Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Pekka Enberg <penberg@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 12 +++++++++---
1 file changed, 9 insertions(+), 3 deletions(-)
diff -puN mm/page_alloc.c~mm-page_alloc-factor-out-setting-of-pcp-high-and-pcp-batch mm/page_alloc.c
--- a/mm/page_alloc.c~mm-page_alloc-factor-out-setting-of-pcp-high-and-pcp-batch
+++ a/mm/page_alloc.c
@@ -4032,6 +4032,14 @@ static int __meminit zone_batchsize(stru
#endif
}
+/* 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);
+}
+
static void setup_pageset(struct per_cpu_pageset *p, unsigned long batch)
{
struct per_cpu_pages *pcp;
@@ -4041,8 +4049,7 @@ static void setup_pageset(struct per_cpu
pcp = &p->pcp;
pcp->count = 0;
- pcp->high = 6 * batch;
- pcp->batch = max(1UL, 1 * batch);
+ pageset_set_batch(p, batch);
for (migratetype = 0; migratetype < MIGRATE_PCPTYPES; migratetype++)
INIT_LIST_HEAD(&pcp->lists[migratetype]);
}
@@ -4051,7 +4058,6 @@ static void setup_pageset(struct per_cpu
* setup_pagelist_highmark() sets the high water mark for hot per_cpu_pagelist
* to the value high for the pageset p.
*/
-
static void setup_pagelist_highmark(struct per_cpu_pageset *p,
unsigned long high)
{
_
Patches currently in -mm which might be from cody@xxxxxxxxxxxxxxxxxx are
mm-page_alloc-factor-out-setting-of-pcp-high-and-pcp-batch.patch
mm-page_alloc-prevent-concurrent-updaters-of-pcp-batch-and-high.patch
mm-page_alloc-insert-memory-barriers-to-allow-async-update-of-pcp-batch-and-high.patch
mm-page_alloc-protect-pcp-batch-accesses-with-access_once.patch
mm-page_alloc-convert-zone_pcp_update-to-rely-on-memory-barriers-instead-of-stop_machine.patch
mm-page_alloc-when-handling-percpu_pagelist_fraction-dont-unneedly-recalulate-high.patch
mm-page_alloc-factor-setup_pageset-into-pageset_init-and-pageset_set_batch.patch
mm-page_alloc-relocate-comment-to-be-directly-above-code-it-refers-to.patch
mm-page_alloc-factor-zone_pageset_init-out-of-setup_zone_pageset.patch
mm-page_alloc-in-zone_pcp_update-uze-zone_pageset_init.patch
mm-page_alloc-rename-setup_pagelist_highmark-to-match-naming-of-pageset_set_batch.patch
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