Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754881AbbGUMyd (ORCPT ); Tue, 21 Jul 2015 08:54:33 -0400 Received: from cantor2.suse.de ([195.135.220.15]:36707 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752635AbbGUMyb (ORCPT ); Tue, 21 Jul 2015 08:54:31 -0400 From: Vlastimil Babka To: Andrew Morton , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, "minkyung88.kim" , kmk3210@gmail.com, Seungho Park , Vlastimil Babka , Joonsoo Kim , Minchan Kim , Michal Nazarewicz , Laura Abbott , Naoya Horiguchi , Johannes Weiner , "Kirill A. Shutemov" , Mel Gorman Subject: [PATCH 1/2] mm, page_isolation: remove bogus tests for isolated pages Date: Tue, 21 Jul 2015 14:53:37 +0200 Message-Id: <1437483218-18703-1-git-send-email-vbabka@suse.cz> X-Mailer: git-send-email 2.4.5 In-Reply-To: <55969822.9060907@suse.cz> References: <55969822.9060907@suse.cz> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3886 Lines: 91 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 Cc: Joonsoo Kim Cc: Minchan Kim Cc: Michal Nazarewicz Cc: Laura Abbott Cc: Naoya Horiguchi --- mm/page_isolation.c | 30 ++++++------------------------ 1 file changed, 6 insertions(+), 24 deletions(-) diff --git a/mm/page_isolation.c b/mm/page_isolation.c index 0e69d25..9eaa489c 100644 --- a/mm/page_isolation.c +++ b/mm/page_isolation.c @@ -226,34 +226,16 @@ __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; } -- 2.4.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/