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Date: Fri, 22 Jun 2012 22:56:52 -0400
From: KOSAKI Motohiro <kosaki.motohiro@...il.com>
To: Minchan Kim <minchan@...nel.org>
CC: Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
KOSAKI Motohiro <kosaki.motohiro@...il.com>,
Aaditya Kumar <aaditya.kumar.30@...il.com>,
Mel Gorman <mel@....ul.ie>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: Accounting problem of MIGRATE_ISOLATED freed page
(6/22/12 2:45 AM), Minchan Kim wrote:
> On 06/22/2012 10:05 AM, Minchan Kim wrote:
>
>> Second approach which is suggested by KOSAKI is what you mentioned.
>> But the concern about second approach is how to make sure matched count increase/decrease of nr_isolated_areas.
>> I mean how to make sure nr_isolated_areas would be zero when isolation is done.
>> Of course, we can investigate all of current caller and make sure they don't make mistake
>> now. But it's very error-prone if we consider future's user.
>> So we might need test_set_pageblock_migratetype(page, MIGRATE_ISOLATE);
>
>
> It's an implementation about above approach.
>
> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index bf3404e..3e9a9e1 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -474,6 +474,11 @@ struct zone {
> * rarely used fields:
> */
> const char *name;
> + /*
> + * the number of MIGRATE_ISOLATE pageblock
> + * We need this for accurate free page counting.
> + */
> + atomic_t nr_migrate_isolate;
#ifdef CONFIG_MEMORY_HOTPLUG?
> } ____cacheline_internodealigned_in_smp;
>
> typedef enum {
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 2c29b1c..6cb1f9f 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -219,6 +219,11 @@ EXPORT_SYMBOL(nr_online_nodes);
>
> int page_group_by_mobility_disabled __read_mostly;
>
> +/*
> + * NOTE:
> + * Don't use set_pageblock_migratetype(page, MIGRATE_ISOLATE) direclty.
> + * Instead, use {un}set_pageblock_isolate.
> + */
> void set_pageblock_migratetype(struct page *page, int migratetype)
> {
> if (unlikely(page_group_by_mobility_disabled))
> @@ -1622,6 +1627,28 @@ bool zone_watermark_ok(struct zone *z, int order, unsigned long mark,
> zone_page_state(z, NR_FREE_PAGES));
> }
>
> +unsigned long migrate_isolate_pages(struct zone *zone)
> +{
> + unsigned long nr_pages = 0;
> +
> + if (unlikely(atomic_read(&zone->nr_migrate_isolate))) {
> + unsigned long flags;
> + int order;
> + spin_lock_irqsave(&zone->lock, flags);
> + for (order = 0; order < MAX_ORDER; order++) {
> + struct free_area *area = &zone->free_area[order];
> + long count = 0;
> + struct list_head *curr;
> +
> + list_for_each(curr, &area->free_list[MIGRATE_ISOLATE])
> + count++;
> + nr_pages += (count << order);
> + }
> + spin_unlock_irqrestore(&zone->lock, flags);
> + }
> + return nr_pages;
> +}
> +
> bool zone_watermark_ok_safe(struct zone *z, int order, unsigned long mark,
> int classzone_idx, int alloc_flags)
> {
> @@ -1630,6 +1657,14 @@ 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, too. Otherwise, kswapd can sleep forever.
> + */
> + free_pages -= migrate_isolate_pages(z);
> + if (free_pages < 0)
> + free_pages = 0;
> +
> return __zone_watermark_ok(z, order, mark, classzone_idx, alloc_flags,
> free_pages);
> }
> @@ -4408,6 +4443,7 @@ static void __paginginit free_area_init_core(struct pglist_data *pgdat,
> lruvec_init(&zone->lruvec, zone);
> zap_zone_vm_stats(zone);
> zone->flags = 0;
> + atomic_set(&zone->nr_migrate_isolate, 0);
> if (!size)
> continue;
>
> @@ -5555,6 +5591,45 @@ bool is_pageblock_removable_nolock(struct page *page)
> return __count_immobile_pages(zone, page, 0);
> }
>
> +static void set_pageblock_isolate(struct zone *zone, struct page *page)
> +{
> + int old_migratetype;
> + assert_spin_locked(&zone->lock);
> +
> + if (unlikely(page_group_by_mobility_disabled)) {
We don't need this check. page_group_by_mobility_disabled is an optimization for
low memory system. but memory hotplug should work even though run on low memory.
In other words, current upstream code is buggy. :-)
> + set_pageblock_flags_group(page, MIGRATE_UNMOVABLE,
> + PB_migrate, PB_migrate_end);
> + return;
> + }
> +
> + old_migratetype = get_pageblock_migratetype(page);
> + set_pageblock_flags_group(page, MIGRATE_ISOLATE,
> + PB_migrate, PB_migrate_end);
> +
> + if (old_migratetype != MIGRATE_ISOLATE)
> + atomic_inc(&zone->nr_migrate_isolate);
> +}
> +
> +static void unset_pageblock_isolate(struct zone *zone, struct page *page,
> + unsigned long migratetype)
> +{
> + assert_spin_locked(&zone->lock);
> +
> + if (unlikely(page_group_by_mobility_disabled)) {
> + set_pageblock_flags_group(page, migratetype,
> + PB_migrate, PB_migrate_end);
> + return;
> + }
> +
> + BUG_ON(get_pageblock_migratetype(page) != MIGRATE_ISOLATE);
> + BUG_ON(migratetype == MIGRATE_ISOLATE);
> +
> + set_pageblock_flags_group(page, migratetype,
> + PB_migrate, PB_migrate_end);
> + atomic_dec(&zone->nr_migrate_isolate);
> + BUG_ON(atomic_read(&zone->nr_migrate_isolate) < 0);
> +}
> +
> int set_migratetype_isolate(struct page *page)
> {
> struct zone *zone;
> @@ -5601,7 +5676,7 @@ int set_migratetype_isolate(struct page *page)
>
> out:
> if (!ret) {
> - set_pageblock_migratetype(page, MIGRATE_ISOLATE);
> + set_pageblock_isolate(zone, page);
> move_freepages_block(zone, page, MIGRATE_ISOLATE);
> }
>
> @@ -5619,8 +5694,8 @@ void unset_migratetype_isolate(struct page *page, unsigned migratetype)
> spin_lock_irqsave(&zone->lock, flags);
> if (get_pageblock_migratetype(page) != MIGRATE_ISOLATE)
> goto out;
> - set_pageblock_migratetype(page, migratetype);
> move_freepages_block(zone, page, migratetype);
> + unset_pageblock_isolate(zone, page, migratetype);
I don't think this order change is unnecessary. Why did you swap?
Other than that, looks very good to me.
> out:
> spin_unlock_irqrestore(&zone->lock, flags);
> }
--
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