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Date: Thu, 20 Sep 2012 14:16:28 +0900
From: Minchan Kim <minchan@...nel.org>
To: Wen Congyang <wency@...fujitsu.com>
Cc: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
KOSAKI Motohiro <kosaki.motohiro@...il.com>,
Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org,
Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
Shaohua Li <shli@...ionio.com>
Subject: Re: [PATCH] memory-hotplug: fix zone stat mismatch
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@...nel.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@...nel.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@...fujitsu.com>
Cc: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
Cc: Wen Congyang <wency@...fujitsu.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Signed-off-by: Minchan Kim <minchan@...nel.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
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