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Date: Mon, 25 Jun 2012 10:10:25 +0900
From: Minchan Kim <minchan@...nel.org>
To: KOSAKI Motohiro <kosaki.motohiro@...il.com>
CC: Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.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
Hi KOSAKI,
On 06/23/2012 11:56 AM, KOSAKI Motohiro wrote:
> (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?
Now I am seeing how to handle CONFIG_{MEMORY_HOTPLUG | CMA | MEMORY_FAILURE}.
>
>
>> } ____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. :-)
If it's a bug, I want to fix it as another patch in next chance all at once.
>
>
>> + 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?
If we don't change it, zone_watermark_pages_ok can see stale the number of free pages because
nr_migrate_isolate count is zero but still remains several pages in MIGRATE_ISOLATE in buddy.
>
>
> Other than that, looks very good to me.
Thanks!
--
Kind regards,
Minchan Kim
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