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SubjectRe: Accounting problem of MIGRATE_ISOLATED freed page
(2012/06/22 15:45), 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.
>

I like this 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;
> } ____cacheline_internodealigned_in_smp;

Isn't this counter modified only under zone->lock ?


>
> 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));
> }

I'm glad if this function can be static...Hm. With easy grep, I think it can be...

Thanks,
-Kame



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