[PATCH resend] mm: drain percpu lru add/rotate page-vectors on cpu hot-unplug

[PATCH resend] mm: drain percpu lru add/rotate page-vectors on cpu hot-unplug

[Konstantin Khlebnikov]

This cpu hotplug hook was accidentally removed in commit v2.6.30-rc4-18-g00a62ce
("mm: fix Committed_AS underflow on large NR_CPUS environment")

Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
---
 include/linux/swap.h |    1 +
 mm/page_alloc.c      |    1 +
 mm/swap.c            |    4 ++--
 3 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index f7df3ea..ba2c8d7 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -229,6 +229,7 @@ extern void lru_add_page_tail(struct zone* zone,
 extern void activate_page(struct page *);
 extern void mark_page_accessed(struct page *);
 extern void lru_add_drain(void);
+extern void lru_add_drain_cpu(int cpu);
 extern int lru_add_drain_all(void);
 extern void rotate_reclaimable_page(struct page *page);
 extern void deactivate_page(struct page *page);
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 864d1b7..2b7f07b 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -4874,6 +4874,7 @@ static int page_alloc_cpu_notify(struct notifier_block *self,
 	int cpu = (unsigned long)hcpu;
 
 	if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
+		lru_add_drain_cpu(cpu);
 		drain_pages(cpu);
 
 		/*
diff --git a/mm/swap.c b/mm/swap.c
index fff1ff7..38b2686 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -496,7 +496,7 @@ static void lru_deactivate_fn(struct page *page, void *arg)
  * Either "cpu" is the current CPU, and preemption has already been
  * disabled; or "cpu" is being hot-unplugged, and is already dead.
  */
-static void drain_cpu_pagevecs(int cpu)
+void lru_add_drain_cpu(int cpu)
 {
 	struct pagevec *pvecs = per_cpu(lru_add_pvecs, cpu);
 	struct pagevec *pvec;
@@ -553,7 +553,7 @@ void deactivate_page(struct page *page)
 
 void lru_add_drain(void)
 {
-	drain_cpu_pagevecs(get_cpu());
+	lru_add_drain_cpu(get_cpu());
 	put_cpu();
 }
 

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Re: [PATCH resend] mm: drain percpu lru add/rotate page-vectors on cpu hot-unplug

[KAMEZAWA Hiroyuki]

On Tue, 28 Feb 2012 23:40:45 +0400
Konstantin Khlebnikov <khlebnikov@openvz.org> wrote:

> This cpu hotplug hook was accidentally removed in commit v2.6.30-rc4-18-g00a62ce
> ("mm: fix Committed_AS underflow on large NR_CPUS environment")
> 
> Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>

Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

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Re: [PATCH resend] mm: drain percpu lru add/rotate page-vectors on cpu hot-unplug

[Andrew Morton]

On Tue, 28 Feb 2012 23:40:45 +0400
Konstantin Khlebnikov <khlebnikov@openvz.org> wrote:

> This cpu hotplug hook was accidentally removed in commit v2.6.30-rc4-18-g00a62ce
> ("mm: fix Committed_AS underflow on large NR_CPUS environment")

That was a long time ago - maybe we should leave it removed ;) I mean,
did this bug(?) have any visible effect?  If so, what was that effect?

IOW, the changelog didn't give anyone any reason to apply the patch to
anything!

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Re: [PATCH resend] mm: drain percpu lru add/rotate page-vectors on cpu hot-unplug

[Konstantin Khlebnikov]

Andrew Morton wrote:
> On Tue, 28 Feb 2012 23:40:45 +0400
> Konstantin Khlebnikov<khlebnikov@openvz.org>  wrote:
>
>> This cpu hotplug hook was accidentally removed in commit v2.6.30-rc4-18-g00a62ce
>> ("mm: fix Committed_AS underflow on large NR_CPUS environment")
>
> That was a long time ago - maybe we should leave it removed ;) I mean,
> did this bug(?) have any visible effect?  If so, what was that effect?

It's because cpu hotplug/unplug isn't widely used feature.
Visible effect -- some pages are borrowed in per-cpu page-vectors.
Truncate can deal with it, but these pages cannot be reused while this cpu is offline.
So this is like temporary memory leak.

>
> IOW, the changelog didn't give anyone any reason to apply the patch to
> anything!

Sorry, I'm just stuck in pile of patches. It seems I should stop and send them one by one.
This one isn't critical, so there no reasons for pushing it into stable branches.

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