On Fri, Nov 18, 2011 at 05:43:08PM +0100, Marek Szyprowski wrote:
From: Michal Nazarewicz mina86@mina86.com
If page is on PCP list while pageblock it belongs to gets isolated, the page's private still holds the old migrate type. This means that free_pcppages_bulk() will put the page on a freelist of the old migrate type instead of MIGRATE_ISOLATE.
This commit changes that by explicitly checking whether page's pageblock's migrate type is MIGRATE_ISOLATE and if it is, overwrites page's private data.
Signed-off-by: Michal Nazarewicz mina86@mina86.com Signed-off-by: Marek Szyprowski m.szyprowski@samsung.com
mm/page_alloc.c | 12 ++++++++++++ 1 files changed, 12 insertions(+), 0 deletions(-)
diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 9dd443d..58d1a2e 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -628,6 +628,18 @@ static void free_pcppages_bulk(struct zone *zone, int count, page = list_entry(list->prev, struct page, lru); /* must delete as __free_one_page list manipulates */ list_del(&page->lru);
/** When page is isolated in set_migratetype_isolate()* function it's page_private is not changed since the* function has no way of knowing if it can touch it.* This means that when a page is on PCP list, it's* page_private no longer matches the desired migrate* type.*/if (get_pageblock_migratetype(page) == MIGRATE_ISOLATE)set_page_private(page, MIGRATE_ISOLATE);
How much of a problem is this in practice? It's adding overhead to the free path for what should be a very rare case which is undesirable. I know we are already calling get_pageblock_migrate() when freeing pages but it should be unnecessary to call it again. I'd go as far to say that it would be preferable to drain the per-CPU lists after you set pageblocks MIGRATE_ISOLATE. The IPIs also have overhead but it will be incurred for the rare rather than the common case.