From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751845AbcFXJ4b (ORCPT ); Fri, 24 Jun 2016 05:56:31 -0400 Received: from mx2.suse.de ([195.135.220.15]:35104 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751431AbcFXJzK (ORCPT ); Fri, 24 Jun 2016 05:55:10 -0400 From: Vlastimil Babka To: Andrew Morton Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Michal Hocko , Mel Gorman , Joonsoo Kim , David Rientjes , Rik van Riel , Vlastimil Babka Subject: [PATCH v3 15/17] mm, compaction: use proper alloc_flags in __compaction_suitable() Date: Fri, 24 Jun 2016 11:54:35 +0200 Message-Id: <20160624095437.16385-16-vbabka@suse.cz> X-Mailer: git-send-email 2.8.4 In-Reply-To: <20160624095437.16385-1-vbabka@suse.cz> References: <20160624095437.16385-1-vbabka@suse.cz> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The __compaction_suitable() function checks the low watermark plus a compact_gap() gap to decide if there's enough free memory to perform compaction. This check uses direct compactor's alloc_flags, but that's wrong, since these flags are not applicable for freepage isolation. For example, alloc_flags may indicate access to memory reserves, making compaction proceed, and then fail watermark check during the isolation. A similar problem exists for ALLOC_CMA, which may be part of alloc_flags, but not during freepage isolation. In this case however it makes sense to use ALLOC_CMA both in __compaction_suitable() and __isolate_free_page(), since there's actually nothing preventing the freepage scanner to isolate from CMA pageblocks, with the assumption that a page that could be migrated once by compaction can be migrated also later by CMA allocation. Thus we should count pages in CMA pageblocks when considering compaction suitability and when isolating freepages. To sum up, this patch should remove some false positives from __compaction_suitable(), and allow compaction to proceed when free pages required for compaction reside in the CMA pageblocks. Signed-off-by: Vlastimil Babka --- mm/compaction.c | 12 ++++++++++-- mm/page_alloc.c | 2 +- 2 files changed, 11 insertions(+), 3 deletions(-) diff --git a/mm/compaction.c b/mm/compaction.c index c1ce7c2abe05..3b774befb62a 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -1396,11 +1396,19 @@ static enum compact_result __compaction_suitable(struct zone *zone, int order, /* * Watermarks for order-0 must be met for compaction to be able to - * isolate free pages for migration targets. + * isolate free pages for migration targets. This means that the + * watermark and alloc_flags have to match, or be more pessimistic than + * the check in __isolate_free_page(). We don't use the direct + * compactor's alloc_flags, as they are not relevant for freepage + * isolation. We however do use the direct compactor's classzone_idx to + * skip over zones where lowmem reserves would prevent allocation even + * if compaction succeeds. + * ALLOC_CMA is used, as pages in CMA pageblocks are considered + * suitable migration targets */ watermark = low_wmark_pages(zone) + compact_gap(order); if (!__zone_watermark_ok(zone, 0, watermark, classzone_idx, - alloc_flags, wmark_target)) + ALLOC_CMA, wmark_target)) return COMPACT_SKIPPED; /* diff --git a/mm/page_alloc.c b/mm/page_alloc.c index e1efdc8d2a52..9510b91517dd 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2503,7 +2503,7 @@ int __isolate_free_page(struct page *page, unsigned int order) if (!is_migrate_isolate(mt)) { /* Obey watermarks as if the page was being allocated */ watermark = low_wmark_pages(zone) + (1 << order); - if (!zone_watermark_ok(zone, 0, watermark, 0, 0)) + if (!zone_watermark_ok(zone, 0, watermark, 0, ALLOC_CMA)) return 0; __mod_zone_freepage_state(zone, -(1UL << order), mt); -- 2.8.4 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f69.google.com (mail-wm0-f69.google.com [74.125.82.69]) by kanga.kvack.org (Postfix) with ESMTP id C5A1C828E4 for ; Fri, 24 Jun 2016 05:55:28 -0400 (EDT) Received: by mail-wm0-f69.google.com with SMTP id a66so13328283wme.1 for ; Fri, 24 Jun 2016 02:55:28 -0700 (PDT) Received: from mx2.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id i76si3229306wmc.31.2016.06.24.02.55.04 for (version=TLS1 cipher=AES128-SHA bits=128/128); Fri, 24 Jun 2016 02:55:04 -0700 (PDT) From: Vlastimil Babka Subject: [PATCH v3 15/17] mm, compaction: use proper alloc_flags in __compaction_suitable() Date: Fri, 24 Jun 2016 11:54:35 +0200 Message-Id: <20160624095437.16385-16-vbabka@suse.cz> In-Reply-To: <20160624095437.16385-1-vbabka@suse.cz> References: <20160624095437.16385-1-vbabka@suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Michal Hocko , Mel Gorman , Joonsoo Kim , David Rientjes , Rik van Riel , Vlastimil Babka The __compaction_suitable() function checks the low watermark plus a compact_gap() gap to decide if there's enough free memory to perform compaction. This check uses direct compactor's alloc_flags, but that's wrong, since these flags are not applicable for freepage isolation. For example, alloc_flags may indicate access to memory reserves, making compaction proceed, and then fail watermark check during the isolation. A similar problem exists for ALLOC_CMA, which may be part of alloc_flags, but not during freepage isolation. In this case however it makes sense to use ALLOC_CMA both in __compaction_suitable() and __isolate_free_page(), since there's actually nothing preventing the freepage scanner to isolate from CMA pageblocks, with the assumption that a page that could be migrated once by compaction can be migrated also later by CMA allocation. Thus we should count pages in CMA pageblocks when considering compaction suitability and when isolating freepages. To sum up, this patch should remove some false positives from __compaction_suitable(), and allow compaction to proceed when free pages required for compaction reside in the CMA pageblocks. Signed-off-by: Vlastimil Babka --- mm/compaction.c | 12 ++++++++++-- mm/page_alloc.c | 2 +- 2 files changed, 11 insertions(+), 3 deletions(-) diff --git a/mm/compaction.c b/mm/compaction.c index c1ce7c2abe05..3b774befb62a 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -1396,11 +1396,19 @@ static enum compact_result __compaction_suitable(struct zone *zone, int order, /* * Watermarks for order-0 must be met for compaction to be able to - * isolate free pages for migration targets. + * isolate free pages for migration targets. This means that the + * watermark and alloc_flags have to match, or be more pessimistic than + * the check in __isolate_free_page(). We don't use the direct + * compactor's alloc_flags, as they are not relevant for freepage + * isolation. We however do use the direct compactor's classzone_idx to + * skip over zones where lowmem reserves would prevent allocation even + * if compaction succeeds. + * ALLOC_CMA is used, as pages in CMA pageblocks are considered + * suitable migration targets */ watermark = low_wmark_pages(zone) + compact_gap(order); if (!__zone_watermark_ok(zone, 0, watermark, classzone_idx, - alloc_flags, wmark_target)) + ALLOC_CMA, wmark_target)) return COMPACT_SKIPPED; /* diff --git a/mm/page_alloc.c b/mm/page_alloc.c index e1efdc8d2a52..9510b91517dd 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2503,7 +2503,7 @@ int __isolate_free_page(struct page *page, unsigned int order) if (!is_migrate_isolate(mt)) { /* Obey watermarks as if the page was being allocated */ watermark = low_wmark_pages(zone) + (1 << order); - if (!zone_watermark_ok(zone, 0, watermark, 0, 0)) + if (!zone_watermark_ok(zone, 0, watermark, 0, ALLOC_CMA)) return 0; __mod_zone_freepage_state(zone, -(1UL << order), mt); -- 2.8.4 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org