From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755215AbdKBMuR (ORCPT ); Thu, 2 Nov 2017 08:50:17 -0400 Received: from mx2.suse.de ([195.135.220.15]:49790 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754958AbdKBMuQ (ORCPT ); Thu, 2 Nov 2017 08:50:16 -0400 From: Vlastimil Babka To: Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Mel Gorman , Joonsoo Kim , Rik van Riel , David Rientjes , Johannes Weiner , Vlastimil Babka Subject: [PATCH] mm, page_alloc: fix potential false positive in __zone_watermark_ok Date: Thu, 2 Nov 2017 13:50:01 +0100 Message-Id: <20171102125001.23708-1-vbabka@suse.cz> X-Mailer: git-send-email 2.14.3 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Since commit 97a16fc82a7c ("mm, page_alloc: only enforce watermarks for order-0 allocations"), __zone_watermark_ok() check for high-order allocations will shortcut per-migratetype free list checks for ALLOC_HARDER allocations, and return true as long as there's free page of any migratetype. The intention is that ALLOC_HARDER can allocate from MIGRATE_HIGHATOMIC free lists, while normal allocations can't. However, as a side effect, the watermark check will then also return true when there are pages only on the MIGRATE_ISOLATE list, or (prior to CMA conversion to ZONE_MOVABLE) on the MIGRATE_CMA list. Since the allocation cannot actually obtain isolated pages, and might not be able to obtain CMA pages, this can result in a false positive. The condition should be rare and perhaps the outcome is not a fatal one. Still, it's better if the watermark check is correct. There also shouldn't be a performance tradeoff here. Fixes: 97a16fc82a7c ("mm, page_alloc: only enforce watermarks for order-0 allocations") Signed-off-by: Vlastimil Babka --- mm/page_alloc.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 79cdac1fee42..f43039945148 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -3032,9 +3032,6 @@ bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark, if (!area->nr_free) continue; - if (alloc_harder) - return true; - for (mt = 0; mt < MIGRATE_PCPTYPES; mt++) { if (!list_empty(&area->free_list[mt])) return true; @@ -3044,6 +3041,9 @@ bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark, if (!list_empty(&area->free_list[MIGRATE_CMA])) return true; #endif + if (alloc_harder && + !list_empty(&area->free_list[MIGRATE_HIGHATOMIC])) + return true; } return false; } -- 2.14.3 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f72.google.com (mail-pg0-f72.google.com [74.125.83.72]) by kanga.kvack.org (Postfix) with ESMTP id D2B1A6B0253 for ; Thu, 2 Nov 2017 08:50:17 -0400 (EDT) Received: by mail-pg0-f72.google.com with SMTP id l23so5903419pgc.10 for ; Thu, 02 Nov 2017 05:50:17 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id j25si3492477pgn.86.2017.11.02.05.50.16 for (version=TLS1 cipher=AES128-SHA bits=128/128); Thu, 02 Nov 2017 05:50:16 -0700 (PDT) From: Vlastimil Babka Subject: [PATCH] mm, page_alloc: fix potential false positive in __zone_watermark_ok Date: Thu, 2 Nov 2017 13:50:01 +0100 Message-Id: <20171102125001.23708-1-vbabka@suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Mel Gorman , Joonsoo Kim , Rik van Riel , David Rientjes , Johannes Weiner , Vlastimil Babka Since commit 97a16fc82a7c ("mm, page_alloc: only enforce watermarks for order-0 allocations"), __zone_watermark_ok() check for high-order allocations will shortcut per-migratetype free list checks for ALLOC_HARDER allocations, and return true as long as there's free page of any migratetype. The intention is that ALLOC_HARDER can allocate from MIGRATE_HIGHATOMIC free lists, while normal allocations can't. However, as a side effect, the watermark check will then also return true when there are pages only on the MIGRATE_ISOLATE list, or (prior to CMA conversion to ZONE_MOVABLE) on the MIGRATE_CMA list. Since the allocation cannot actually obtain isolated pages, and might not be able to obtain CMA pages, this can result in a false positive. The condition should be rare and perhaps the outcome is not a fatal one. Still, it's better if the watermark check is correct. There also shouldn't be a performance tradeoff here. Fixes: 97a16fc82a7c ("mm, page_alloc: only enforce watermarks for order-0 allocations") Signed-off-by: Vlastimil Babka --- mm/page_alloc.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 79cdac1fee42..f43039945148 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -3032,9 +3032,6 @@ bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark, if (!area->nr_free) continue; - if (alloc_harder) - return true; - for (mt = 0; mt < MIGRATE_PCPTYPES; mt++) { if (!list_empty(&area->free_list[mt])) return true; @@ -3044,6 +3041,9 @@ bool __zone_watermark_ok(struct zone *z, unsigned int order, unsigned long mark, if (!list_empty(&area->free_list[MIGRATE_CMA])) return true; #endif + if (alloc_harder && + !list_empty(&area->free_list[MIGRATE_HIGHATOMIC])) + return true; } return false; } -- 2.14.3 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. 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