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@xxxxxxxxxx> 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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