Re: [PATCH] memory-hotplug: fix zone stat mismatch

[Minchan Kim <minchan@kernel.org>]

On Thu, Sep 20, 2012 at 11:12:40AM +0800, Wen Congyang wrote:
> At 09/20/2012 10:30 AM, Minchan Kim Wrote:
> > On Thu, Sep 20, 2012 at 09:17:43AM +0800, Wen Congyang wrote:
> >> At 09/20/2012 04:17 AM, Minchan Kim Wrote:
> >>> Hi KOSAKI,
> >>>
> >>> On Wed, Sep 19, 2012 at 02:05:20PM -0400, KOSAKI Motohiro wrote:
> >>>> On Wed, Sep 19, 2012 at 3:29 AM, Minchan Kim <minchan@kernel.org> wrote:
> >>>>> During memory-hotplug stress test, I found NR_ISOLATED_[ANON|FILE]
> >>>>> are increasing so that kernel are hang out.
> >>>>>
> >>>>> The cause is that when we do memory-hotadd after memory-remove,
> >>>>> __zone_pcp_update clear out zone's ZONE_STAT_ITEMS in setup_pageset
> >>>>> without draining vm_stat_diff of all CPU.
> >>>>>
> >>>>> This patch fixes it.
> >>>>
> >>>> zone_pcp_update() is called from online pages path. but IMHO,
> >>>> the statistics should be drained offline path. isn't it?
> >>>
> >>> It isn't necessary because statistics is right until we reset it to zero
> >>> in online path.
> >>> Do you have something on your mind that we have to drain it in offline path?
> >>
> >> When a node is offlined and onlined again. We create node_data[i] in the
> > 
> > I would like to clarify your word.
> > Create or recreate?
> > Why I have a question is as I look over the source code, hotadd_new_pgdat
> > seem to be called if we do hotadd *new* memory. It's not the case for
> > offline and online again you mentioned. If you're right, I should find 
> > arch_free_nodedata to free pgdat when node is disappear but I can't find it.
> > Do I miss something?
> 
> Hmm, when a memory is removed, we don't do cleanup now. We(Fujitsu) posted
> a patchset to do this:
> https://lkml.org/lkml/2012/9/5/201
> 
> We don't free pgdat in this patchset now. We have two choice:
> 1. free pgdat
> 2. don't free it, and reuse it when it is onlined again
> 
> I'm not sure which choice is better.

I have no idea because I don't know how you guys uses.
If there is use case that sometime you ues many node burstly but
ues a few node in most time, 1) would be good POV memory efficiency
although it makes code rather complicated.

Anyway, it's another story with this patch because it's not merged yet.

> 
> > 
> > 
> >> function hotadd_new_pgdat(), and we will lost the statistics stored in
> >> zone->pageset. So we should drain it in offline path.
> > 
> > Even we drain in offline patch, it still has a problem.
> > 
> > 1. offline
> > 2. drain -> OKAY 
> > 3. schedule
> > 4. Process A increase zone stat
> > 5. Process B increase zone stat
> > 6. online
> > 7. reset it -> we ends up lost zone stat counter which is modified between 2-6
> > 
> 
> I understand why you drain it in online path now. But it still should drain it
> in offline path because if all pages in this zone are offlined, we will call
> zone_pcp_reset() to reset zone's pcp. We should also drop it in the function
> zone_pcp_reset().

Good point.
How about this?

>From e92bf3e96720c89cb18ec32c5db095a27ad4133c Mon Sep 17 00:00:00 2001
From: Minchan Kim <minchan@kernel.org>
Date: Thu, 20 Sep 2012 14:11:49 +0900
Subject: [PATCH v2] memory-hotplug: fix zone stat mismatch

During memory-hotplug, I found NR_ISOLATED_[ANON|FILE]
are increasing so that kernel are hang out.

The cause is that when we do memory-hotadd after memory-remove,
__zone_pcp_update clear out zone's ZONE_STAT_ITEMS in setup_pageset
although vm_stat_diff of all CPU still have value.

In addtion, when we offline all pages of the zone, we reset them
in zone_pcp_reset without drain so that we lost zone stat item.

This patch fixes it.

* from v1
  * drain offline patch - KOSAKI, Wen

Cc: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
Cc: Wen Congyang <wency@cn.fujitsu.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 include/linux/vmstat.h |    4 ++++
 mm/page_alloc.c        |    7 +++++++
 mm/vmstat.c            |   12 ++++++++++++
 3 files changed, 23 insertions(+)

diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index ad2cfd5..5d31876 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -198,6 +198,8 @@ extern void __dec_zone_state(struct zone *, enum zone_stat_item);
 void refresh_cpu_vm_stats(int);
 void refresh_zone_stat_thresholds(void);
 
+void drain_zonestat(struct zone *zone, struct per_cpu_pageset *);
+
 int calculate_pressure_threshold(struct zone *zone);
 int calculate_normal_threshold(struct zone *zone);
 void set_pgdat_percpu_threshold(pg_data_t *pgdat,
@@ -251,6 +253,8 @@ static inline void __dec_zone_page_state(struct page *page,
 static inline void refresh_cpu_vm_stats(int cpu) { }
 static inline void refresh_zone_stat_thresholds(void) { }
 
+static inline void drain_zonestat(struct zone *zone,
+			struct per_cpu_pageset *pset) { }
 #endif		/* CONFIG_SMP */
 
 extern const char * const vmstat_text[];
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index ab58346..980f2e7 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5904,6 +5904,7 @@ static int __meminit __zone_pcp_update(void *data)
 		local_irq_save(flags);
 		if (pcp->count > 0)
 			free_pcppages_bulk(zone, pcp->count, pcp);
+		drain_zonestat(zone, pset);
 		setup_pageset(pset, batch);
 		local_irq_restore(flags);
 	}
@@ -5920,10 +5921,16 @@ void __meminit zone_pcp_update(struct zone *zone)
 void zone_pcp_reset(struct zone *zone)
 {
 	unsigned long flags;
+	int cpu;
+	struct per_cpu_pageset *pset;
 
 	/* avoid races with drain_pages()  */
 	local_irq_save(flags);
 	if (zone->pageset != &boot_pageset) {
+		for_each_online_cpu(cpu) {
+			pset = per_cpu_ptr(zone->pageset, cpu);
+			drain_zonestat(zone, pset);
+		}
 		free_percpu(zone->pageset);
 		zone->pageset = &boot_pageset;
 	}
diff --git a/mm/vmstat.c b/mm/vmstat.c
index b3e3b9d..d4cc1c2 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -495,6 +495,18 @@ void refresh_cpu_vm_stats(int cpu)
 			atomic_long_add(global_diff[i], &vm_stat[i]);
 }
 
+void drain_zonestat(struct zone *zone, struct per_cpu_pageset *pset)
+{
+	int i;
+
+	for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)
+		if (pset->vm_stat_diff[i]) {
+			int v = pset->vm_stat_diff[i];
+			pset->vm_stat_diff[i] = 0;
+			atomic_long_add(v, &zone->vm_stat[i]);
+			atomic_long_add(v, &vm_stat[i]);
+		}
+}
 #endif
 
 #ifdef CONFIG_NUMA
-- 
1.7.9.5





-- 
Kind regards,
Minchan Kim