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    SubjectRe: [PATCH -mm v2] mm: have order > 0 compaction start off where it left
    On 07/03/2012 09:57 AM, Rik van Riel wrote:

    > On 07/02/2012 01:42 PM, Sasha Levin wrote:
    >> On Thu, 2012-06-28 at 14:35 -0700, Andrew Morton wrote:
    >>> On Thu, 28 Jun 2012 17:24:25 -0400 Rik van Riel<riel@redhat.com> wrote:
    >>>>
    >>>>>> @@ -463,6 +474,8 @@ static void isolate_freepages(struct zone *zone,
    >>>>>> */
    >>>>>> if (isolated)
    >>>>>> high_pfn = max(high_pfn, pfn);
    >>>>>> + if (cc->order> 0)
    >>>>>> + zone->compact_cached_free_pfn = high_pfn;
    >>>>>
    >>>>> Is high_pfn guaranteed to be aligned to pageblock_nr_pages here? I
    >>>>> assume so, if lots of code in other places is correct but it's
    >>>>> unobvious from reading this function.
    >>>>
    >>>> Reading the code a few more times, I believe that it is
    >>>> indeed aligned to pageblock size.
    >>>
    >>> I'll slip this into -next for a while.
    >>>
    >>> ---
    >>> a/mm/compaction.c~isolate_freepages-check-that-high_pfn-is-aligned-as-expected
    >>>
    >>> +++ a/mm/compaction.c
    >>> @@ -456,6 +456,7 @@ static void isolate_freepages(struct zon
    >>> }
    >>> spin_unlock_irqrestore(&zone->lock, flags);
    >>>
    >>> + WARN_ON_ONCE(high_pfn& (pageblock_nr_pages - 1));
    >>> /*
    >>> * Record the highest PFN we isolated pages from.
    >>> When next
    >>> * looking for free pages, the search will restart
    >>> here as
    >>
    >> I've triggered the following with today's -next:
    >
    > I've been staring at the migrate code for most of the afternoon,
    > and am not sure how this is triggered.
    >
    > At this point, I'm going to focus my attention on addressing
    > Minchan's comments on my code, and hoping someone who is more
    > familiar with the migrate code knows how high_pfn ends up
    > being not pageblock_nr_pages aligned...
    >


    migrate_pfn does not necessarily start aligned to a pageblock.

    /* Setup to move all movable pages to the end of the zone */
    cc->migrate_pfn = zone->zone_start_pfn;

    In isolate_freepages, high_pfn = low_pfn = cc->migrate_pfn + pageblock_nr_pages /* migrate_pfn doesn't aligned to a pageblock */

    --
    Kind regards,
    Minchan Kim


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