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    SubjectRe: [PATCH 08/15] mm: mmzone: MIGRATE_CMA migration type added
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    From
    > On Thu, Jan 26, 2012 at 10:00:50AM +0100, Marek Szyprowski wrote:
    >> From: Michal Nazarewicz <mina86@mina86.com>
    >> @@ -875,10 +895,15 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,
    >> * This array describes the order lists are fallen back to when
    >> * the free lists for the desirable migrate type are depleted
    >> */
    >> -static int fallbacks[MIGRATE_TYPES][3] = {
    >> +static int fallbacks[MIGRATE_TYPES][4] = {
    >> [MIGRATE_UNMOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_MOVABLE, MIGRATE_RESERVE },
    >> [MIGRATE_RECLAIMABLE] = { MIGRATE_UNMOVABLE, MIGRATE_MOVABLE, MIGRATE_RESERVE },
    >> +#ifdef CONFIG_CMA
    >> + [MIGRATE_MOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE, MIGRATE_CMA , MIGRATE_RESERVE },

    On Mon, 30 Jan 2012 13:35:42 +0100, Mel Gorman <mel@csn.ul.ie> wrote:
    > This is a curious choice. MIGRATE_CMA is allowed to contain movable
    > pages. By using MIGRATE_RECLAIMABLE and MIGRATE_UNMOVABLE for movable
    > pages instead of MIGRATE_CMA, you increase the changes that unmovable
    > pages will need to use MIGRATE_MOVABLE in the future which impacts
    > fragmentation avoidance. I would recommend that you change this to
    >
    > { MIGRATE_CMA, MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE, MIGRATE_RESERVE }

    At the beginning the idea was to try hard not to get pages from MIGRATE_CMA
    allocated at all, thus it was put at the end of the fallbacks list, but on
    a busy system this probably won't help anyway, so I'll change it per your
    suggestion.

    >> @@ -1017,11 +1049,14 @@ __rmqueue_fallback(struct zone *zone, int order, int start_migratetype)
    >> rmv_page_order(page);
    >>
    >> /* Take ownership for orders >= pageblock_order */
    >> - if (current_order >= pageblock_order)
    >> + if (current_order >= pageblock_order &&
    >> + !is_pageblock_cma(page))
    >> change_pageblock_range(page, current_order,
    >> start_migratetype);
    >>
    >> - expand(zone, page, order, current_order, area, migratetype);
    >> + expand(zone, page, order, current_order, area,
    >> + is_migrate_cma(start_migratetype)
    >> + ? start_migratetype : migratetype);
    >>
    >
    > What is this check meant to be doing?
    >
    > start_migratetype is determined by allocflags_to_migratetype() and
    > that never will be MIGRATE_CMA so is_migrate_cma(start_migratetype)
    > should always be false.

    Right, thanks! This should be the other way around, ie.:

    + expand(zone, page, order, current_order, area,
    + is_migrate_cma(migratetype)
    + ? migratetype : start_migratetype);

    I'll fix this and the calls to is_pageblock_cma().

    --
    Best regards, _ _
    .o. | Liege of Serenely Enlightened Majesty of o' \,=./ `o
    ..o | Computer Science, Michał “mina86” Nazarewicz (o o)
    ooo +----<email/xmpp: mpn@google.com>--------------ooO--(_)--Ooo--
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