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SubjectRe: [PATCH] mm: get rid of unnecessary pageblock scanning in setup_zone_migrate_reserve
On Wed, Oct 30, 2013 at 04:19:07PM -0400, KOSAKI Motohiro wrote:
> >@@ -3926,11 +3929,11 @@ static void setup_zone_migrate_reserve(struct zone *zone)
> > /*
> > * Reserve blocks are generally in place to help high-order atomic
> > * allocations that are short-lived. A min_free_kbytes value that
> >- * would result in more than 2 reserve blocks for atomic allocations
> >- * is assumed to be in place to help anti-fragmentation for the
> >- * future allocation of hugepages at runtime.
> >+ * would result in more than MAX_MIGRATE_RESERVE_BLOCKS reserve blocks
> >+ * for atomic allocations is assumed to be in place to help
> >+ * anti-fragmentation for the future allocation of hugepages at runtime.
> > */
> >- reserve = min(2, reserve);
> >+ reserve = min(MAX_MIGRATE_RESERVE_BLOCKS, reserve);
> >
> > for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages) {
> > if (!pfn_valid(pfn))
> >@@ -3956,6 +3959,7 @@ static void setup_zone_migrate_reserve(struct zone *zone)
> > /* If this block is reserved, account for it */
> > if (block_migratetype == MIGRATE_RESERVE) {
> > reserve--;
> >+ found++;
> > continue;
> > }
> >
> >@@ -3970,6 +3974,10 @@ static void setup_zone_migrate_reserve(struct zone *zone)
> > }
> > }
> >
> >+ /* If all possible reserve blocks have been found, we're done */
> >+ if (found >= MAX_MIGRATE_RESERVE_BLOCKS)
> >+ break;
> >+
> > /*
> > * If the reserve is met and this is a previous reserved block,
> > * take it back
>
> Nit. I would like to add following hunk. This is just nit because moving
> reserve pageblock is extreme rare.
>
> if (block_migratetype == MIGRATE_RESERVE) {
> + found++;
> set_pageblock_migratetype(page, MIGRATE_MOVABLE);
> move_freepages_block(zone, page, MIGRATE_MOVABLE);
> }

I don't really see the advantage but if you think it is necessary then I
do not object either.

--
Mel Gorman
SUSE Labs


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