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    SubjectRe: [PATCH -mm v2] mm: have order > 0 compaction start off where it left
    On Wed, Jul 04, 2012 at 12:42:19AM -0700, Andrew Morton wrote:
    > On Wed, 04 Jul 2012 11:34:09 +0900 Minchan Kim <minchan@kernel.org> wrote:
    >
    > > > The rest of this patch takes care to ensure that
    > > > ->compact_cached_free_pfn is aligned to pageblock_nr_pages. But it now
    > > > appears that this particular site will violate that.
    > > >
    > > > What's up? Do we need to fix this site, or do we remove all that
    > > > make-compact_cached_free_pfn-aligned code?
    > >
    > >
    > > I vote removing the warning because it doesn't related to Rik's incremental compaction.
    > > Let's see.
    > >
    > > high_pfn = min(low_pfn, pfn) = cc->migrate_pfn + pageblock_nr_pages.
    > > In here, cc->migrate_pfn isn't necessarily pageblock aligined.
    > > So if we don't consider compact_cached_free_pfn, it can hit.
    > >
    > > static void isolate_freepages()
    > > {
    > > high_pfn = min(low_pfn, pfn) = cc->migrate_pfn + pageblock_nr_pages;
    > > for (..) {
    > > ...
    > > WARN_ON_ONCE(high_pfn & (pageblock_nr_pages - 1));
    > >
    > > }
    > > }
    >
    > Please, look at the patch. In numerous places it is aligning
    > compact_cached_free_pfn to a multiple of pageblock_nr_pages. But in
    > one place it doesn't do that. So are all those alignment operations
    > necessary?
    >

    I don't think the alignments are necessary. The main importance is that
    it does not leave the zone.

    --
    Mel Gorman
    SUSE Labs


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