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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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