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Date: Thu, 12 Jul 2012 14:01:54 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Minchan Kim <minchan@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
Mel Gorman <mgorman@...e.de>,
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
Aaditya Kumar <aaditya.kumar@...sony.com>
Subject: Re: [PATCH 3/3 v3] memory-hotplug: fix kswapd looping forever
problem
On Thu, 12 Jul 2012 11:50:49 +0900
Minchan Kim <minchan@...nel.org> wrote:
> When hotplug offlining happens on zone A, it starts to mark freed page
> as MIGRATE_ISOLATE type in buddy for preventing further allocation.
> (MIGRATE_ISOLATE is very irony type because it's apparently on buddy
> but we can't allocate them).
> When the memory shortage happens during hotplug offlining,
> current task starts to reclaim, then wake up kswapd.
> Kswapd checks watermark, then go sleep because current zone_watermark_ok_safe
> doesn't consider MIGRATE_ISOLATE freed page count.
> Current task continue to reclaim in direct reclaim path without kswapd's helping.
> The problem is that zone->all_unreclaimable is set by only kswapd
> so that current task would be looping forever like below.
>
> __alloc_pages_slowpath
> restart:
> wake_all_kswapd
> rebalance:
> __alloc_pages_direct_reclaim
> do_try_to_free_pages
> if global_reclaim && !all_unreclaimable
> return 1; /* It means we did did_some_progress */
> skip __alloc_pages_may_oom
> should_alloc_retry
> goto rebalance;
>
> If we apply KOSAKI's patch[1] which doesn't depends on kswapd
> about setting zone->all_unreclaimable, we can solve this problem
> by killing some task in direct reclaim path. But it doesn't wake up kswapd, still.
> It could be a problem still if other subsystem needs GFP_ATOMIC request.
> So kswapd should consider MIGRATE_ISOLATE when it calculate free pages
> BEFORE going sleep.
>
> This patch counts the number of MIGRATE_ISOLATE page block and
> zone_watermark_ok_safe will consider it if the system has such blocks
> (fortunately, it's very rare so no problem in POV overhead and kswapd is never
> hotpath).
>
> Copy/modify from Mel's quote
> "
> Ideal solution would be "allocating" the pageblock.
> It would keep the free space accounting as it is but historically,
> memory hotplug didn't allocate pages because it would be difficult to
> detect if a pageblock was isolated or if part of some balloon.
> Allocating just full pageblocks would work around this, However,
> it would play very badly with CMA.
> "
>
> [1] http://lkml.org/lkml/2012/6/14/74
>
> ...
>
> +#ifdef CONFIG_MEMORY_ISOLATION
> +static inline unsigned long nr_zone_isolate_freepages(struct zone *zone)
> +{
> + unsigned long nr_pages = 0;
> +
> + if (unlikely(zone->nr_pageblock_isolate)) {
> + nr_pages = zone->nr_pageblock_isolate * pageblock_nr_pages;
> + }
> + return nr_pages;
> +}
That's pretty verbose. I couldn't resist fiddling with it ;)
> +#else
> +static inline unsigned long nr_zone_isolate_freepages(struct zone *zone)
> +{
> + return 0;
> +}
> +#endif
> +
> bool zone_watermark_ok(struct zone *z, int order, unsigned long mark,
> int classzone_idx, int alloc_flags)
> {
> @@ -1633,6 +1655,14 @@ bool zone_watermark_ok_safe(struct zone *z, int order, unsigned long mark,
> if (z->percpu_drift_mark && free_pages < z->percpu_drift_mark)
> free_pages = zone_page_state_snapshot(z, NR_FREE_PAGES);
>
> + /*
> + * If the zone has MIGRATE_ISOLATE type free page,
> + * we should consider it. nr_zone_isolate_freepages is never
> + * accurate so kswapd might not sleep although she can.
> + * But it's more desirable for memory hotplug rather than
> + * forever sleep which cause livelock in direct reclaim path.
> + */
I had a go at clarifying this comment. Please review the result.
> + free_pages -= nr_zone_isolate_freepages(z);
> return __zone_watermark_ok(z, order, mark, classzone_idx, alloc_flags,
> free_pages);
> }
> @@ -4397,6 +4427,7 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat,
> lruvec_init(&zone->lruvec, zone);
> zap_zone_vm_stats(zone);
> zone->flags = 0;
> + zone->nr_pageblock_isolate = 0;
> if (!size)
> continue;
>
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index fb482cf..64abb33 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -8,6 +8,31 @@
> #include <linux/memory.h>
> #include "internal.h"
>
> +/* called by holding zone->lock */
> +static void set_pageblock_isolate(struct zone *zone, struct page *page)
> +{
> + BUG_ON(page_zone(page) != zone);
Well. If this is the case then why not eliminate this function's
`zone' argument?
> + if (get_pageblock_migratetype(page) == MIGRATE_ISOLATE)
> + return;
> +
> + set_pageblock_migratetype(page, MIGRATE_ISOLATE);
> + zone->nr_pageblock_isolate++;
> +}
> +
> +/* called by holding zone->lock */
> +static void restore_pageblock_isolate(struct zone *zone, struct page *page,
> + int migratetype)
> +{
> + BUG_ON(page_zone(page) != zone);
ditto
> + if (WARN_ON(get_pageblock_migratetype(page) != MIGRATE_ISOLATE))
> + return;
> +
> + BUG_ON(zone->nr_pageblock_isolate <= 0);
> + set_pageblock_migratetype(page, migratetype);
> + zone->nr_pageblock_isolate--;
> +}
From: Andrew Morton <akpm@...ux-foundation.org>
Subject: memory-hotplug-fix-kswapd-looping-forever-problem-fix
simplify nr_zone_isolate_freepages(), rework zone_watermark_ok_safe() comment, simplify set_pageblock_isolate() and restore_pageblock_isolate().
Cc: Aaditya Kumar <aaditya.kumar.30@...il.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc: Mel Gorman <mgorman@...e.de>
Cc: Michal Hocko <mhocko@...e.cz>
Cc: Minchan Kim <minchan@...nel.org>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
---
mm/page_alloc.c | 19 ++++++++-----------
mm/page_isolation.c | 19 ++++++++-----------
2 files changed, 16 insertions(+), 22 deletions(-)
diff -puN include/linux/mmzone.h~memory-hotplug-fix-kswapd-looping-forever-problem-fix include/linux/mmzone.h
diff -puN mm/page_alloc.c~memory-hotplug-fix-kswapd-looping-forever-problem-fix mm/page_alloc.c
--- a/mm/page_alloc.c~memory-hotplug-fix-kswapd-looping-forever-problem-fix
+++ a/mm/page_alloc.c
@@ -1626,12 +1626,9 @@ static bool __zone_watermark_ok(struct z
#ifdef CONFIG_MEMORY_ISOLATION
static inline unsigned long nr_zone_isolate_freepages(struct zone *zone)
{
- unsigned long nr_pages = 0;
-
- if (unlikely(zone->nr_pageblock_isolate)) {
- nr_pages = zone->nr_pageblock_isolate * pageblock_nr_pages;
- }
- return nr_pages;
+ if (unlikely(zone->nr_pageblock_isolate))
+ return zone->nr_pageblock_isolate * pageblock_nr_pages;
+ return 0;
}
#else
static inline unsigned long nr_zone_isolate_freepages(struct zone *zone)
@@ -1656,11 +1653,11 @@ bool zone_watermark_ok_safe(struct zone
free_pages = zone_page_state_snapshot(z, NR_FREE_PAGES);
/*
- * If the zone has MIGRATE_ISOLATE type free page,
- * we should consider it. nr_zone_isolate_freepages is never
- * accurate so kswapd might not sleep although she can.
- * But it's more desirable for memory hotplug rather than
- * forever sleep which cause livelock in direct reclaim path.
+ * If the zone has MIGRATE_ISOLATE type free pages, we should consider
+ * it. nr_zone_isolate_freepages is never accurate so kswapd might not
+ * sleep although it could do so. But this is more desirable for memory
+ * hotplug than sleeping which can cause a livelock in the direct
+ * reclaim path.
*/
free_pages -= nr_zone_isolate_freepages(z);
return __zone_watermark_ok(z, order, mark, classzone_idx, alloc_flags,
diff -puN mm/page_isolation.c~memory-hotplug-fix-kswapd-looping-forever-problem-fix mm/page_isolation.c
--- a/mm/page_isolation.c~memory-hotplug-fix-kswapd-looping-forever-problem-fix
+++ a/mm/page_isolation.c
@@ -8,23 +8,20 @@
#include <linux/memory.h>
#include "internal.h"
-/* called by holding zone->lock */
-static void set_pageblock_isolate(struct zone *zone, struct page *page)
+/* called while holding zone->lock */
+static void set_pageblock_isolate(struct page *page)
{
- BUG_ON(page_zone(page) != zone);
-
if (get_pageblock_migratetype(page) == MIGRATE_ISOLATE)
return;
set_pageblock_migratetype(page, MIGRATE_ISOLATE);
- zone->nr_pageblock_isolate++;
+ page_zone(page)->nr_pageblock_isolate++;
}
-/* called by holding zone->lock */
-static void restore_pageblock_isolate(struct zone *zone, struct page *page,
- int migratetype)
+/* called while holding zone->lock */
+static void restore_pageblock_isolate(struct page *page, int migratetype)
{
- BUG_ON(page_zone(page) != zone);
+ struct zone *zone = page_zone(page);
if (WARN_ON(get_pageblock_migratetype(page) != MIGRATE_ISOLATE))
return;
@@ -79,7 +76,7 @@ int set_migratetype_isolate(struct page
out:
if (!ret) {
- set_pageblock_isolate(zone, page);
+ set_pageblock_isolate(page);
move_freepages_block(zone, page, MIGRATE_ISOLATE);
}
@@ -98,7 +95,7 @@ void unset_migratetype_isolate(struct pa
if (get_pageblock_migratetype(page) != MIGRATE_ISOLATE)
goto out;
move_freepages_block(zone, page, migratetype);
- restore_pageblock_isolate(zone, page, migratetype);
+ restore_pageblock_isolate(page, migratetype);
out:
spin_unlock_irqrestore(&zone->lock, flags);
}
_
--
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