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authorVlastimil Babka <vbabka@suse.cz>2015-09-08 15:01:22 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2015-09-08 15:35:28 -0700
commitaa016d145d4c3b8a7273429528f19d5b423ddbc7 (patch)
tree9af9eb30f650e202cdb3fc97a2959ef352fc5940
parent156408c0edaacbea1137f58b28fd6ec341064310 (diff)
mm, page_isolation: remove bogus tests for isolated pages
The __test_page_isolated_in_pageblock() is used to verify whether all pages in pageblock were either successfully isolated, or are hwpoisoned. Two of the possible state of pages, that are tested, are however bogus and misleading. Both tests rely on get_freepage_migratetype(page), which however has no guarantees about pages on freelists. Specifically, it doesn't guarantee that the migratetype returned by the function actually matches the migratetype of the freelist that the page is on. Such guarantee is not its purpose and would have negative impact on allocator performance. The first test checks whether the freepage_migratetype equals MIGRATE_ISOLATE, supposedly to catch races between page isolation and allocator activity. These races should be fixed nowadays with 51bb1a4093 ("mm/page_alloc: add freepage on isolate pageblock to correct buddy list") and related patches. As explained above, the check wouldn't be able to catch them reliably anyway. For the same reason false positives can happen, although they are harmless, as the move_freepages() call would just move the page to the same freelist it's already on. So removing the test is not a bug fix, just cleanup. After this patch, we assume that all PageBuddy pages are on the correct freelist and that the races were really fixed. A truly reliable verification in the form of e.g. VM_BUG_ON() would be complicated and is arguably not needed. The second test (page_count(page) == 0 && get_freepage_migratetype(page) == MIGRATE_ISOLATE) is probably supposed (the code comes from a big memory isolation patch from 2007) to catch pages on MIGRATE_ISOLATE pcplists. However, pcplists don't contain MIGRATE_ISOLATE freepages nowadays, those are freed directly to free lists, so the check is obsolete. Remove it as well. Signed-off-by: Vlastimil Babka <vbabka@suse.cz> Acked-by: Joonsoo Kim <iamjoonsoo.kim@lge.com> Cc: Minchan Kim <minchan@kernel.org> Acked-by: Michal Nazarewicz <mina86@mina86.com> Cc: Laura Abbott <lauraa@codeaurora.org> Reviewed-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Cc: Seungho Park <seungho1.park@lge.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Acked-by: Mel Gorman <mgorman@techsingularity.net> Cc: David Rientjes <rientjes@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/page_alloc.c4
-rw-r--r--mm/page_isolation.c30
2 files changed, 10 insertions, 24 deletions
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 5f9394df19bf..a329cfaf634d 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -788,7 +788,11 @@ 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);
+
mt = get_freepage_migratetype(page);
+ /* MIGRATE_ISOLATE page should not go to pcplists */
+ VM_BUG_ON_PAGE(is_migrate_isolate(mt), page);
+ /* Pageblock could have been isolated meanwhile */
if (unlikely(has_isolate_pageblock(zone)))
mt = get_pageblock_migratetype(page);
diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index 303c908790ef..32fdc1df05e5 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -223,34 +223,16 @@ __test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn,
continue;
}
page = pfn_to_page(pfn);
- if (PageBuddy(page)) {
+ if (PageBuddy(page))
/*
- * If race between isolatation and allocation happens,
- * some free pages could be in MIGRATE_MOVABLE list
- * although pageblock's migratation type of the page
- * is MIGRATE_ISOLATE. Catch it and move the page into
- * MIGRATE_ISOLATE list.
+ * If the page is on a free list, it has to be on
+ * the correct MIGRATE_ISOLATE freelist. There is no
+ * simple way to verify that as VM_BUG_ON(), though.
*/
- if (get_freepage_migratetype(page) != MIGRATE_ISOLATE) {
- struct page *end_page;
-
- end_page = page + (1 << page_order(page)) - 1;
- move_freepages(page_zone(page), page, end_page,
- MIGRATE_ISOLATE);
- }
pfn += 1 << page_order(page);
- }
- else if (page_count(page) == 0 &&
- get_freepage_migratetype(page) == MIGRATE_ISOLATE)
- pfn += 1;
- else if (skip_hwpoisoned_pages && PageHWPoison(page)) {
- /*
- * The HWPoisoned page may be not in buddy
- * system, and page_count() is not 0.
- */
+ else if (skip_hwpoisoned_pages && PageHWPoison(page))
+ /* A HWPoisoned page cannot be also PageBuddy */
pfn++;
- continue;
- }
else
break;
}