[PATCH 01/11] mm: page_alloc: handle MIGRATE_ISOLATE in free_pcppages_bulk()
From: Mel Gorman <hidden>
Date: 2011-12-12 13:42:44
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linux-media, linux-mm, lkml
On Fri, Nov 18, 2011 at 05:43:08PM +0100, Marek Szyprowski wrote:
quoted hunk ↗ jump to hunk
From: Michal Nazarewicz <redacted> 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 <redacted> 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. -- Mel Gorman SUSE Labs