From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752236AbcJKEeU (ORCPT ); Tue, 11 Oct 2016 00:34:20 -0400 Received: from LGEAMRELO12.lge.com ([156.147.23.52]:34781 "EHLO lgeamrelo12.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751423AbcJKEeT (ORCPT ); Tue, 11 Oct 2016 00:34:19 -0400 X-Original-SENDERIP: 156.147.1.121 X-Original-MAILFROM: minchan@kernel.org X-Original-SENDERIP: 10.177.223.161 X-Original-MAILFROM: minchan@kernel.org Date: Tue, 11 Oct 2016 13:19:16 +0900 From: Minchan Kim To: Vlastimil Babka Cc: Andrew Morton , Mel Gorman , Joonsoo Kim , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Sangseok Lee Subject: Re: [PATCH 1/4] mm: adjust reserved highatomic count Message-ID: <20161011041916.GA30973@bbox> References: <1475819136-24358-1-git-send-email-minchan@kernel.org> <1475819136-24358-2-git-send-email-minchan@kernel.org> <7ac7c0d8-4b7b-e362-08e7-6d62ee20f4c3@suse.cz> <20161007142919.GA3060@bbox> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Vlasimil, On Mon, Oct 10, 2016 at 08:57:40AM +0200, Vlastimil Babka wrote: > On 10/07/2016 04:29 PM, Minchan Kim wrote: > >>>In that case, we should adjust nr_reserved_highatomic. > >>>Otherwise, VM cannot reserve highorderatomic pageblocks any more > >>>although it doesn't reach 1% limit. It means highorder atomic > >>>allocation failure would be higher. > >>> > >>>So, this patch decreases the account as well as migratetype > >>>if it was MIGRATE_HIGHATOMIC. > >>> > >>>Signed-off-by: Minchan Kim > >> > >>Hm wouldn't it be simpler just to prevent the pageblock's migratetype to be > >>changed if it's highatomic? Possibly also not do move_freepages_block() in > > > >It could be. Actually, I did it with modifying can_steal_fallback which returns > >false it found the pageblock is highorderatomic but changed to this way again > >because I don't have any justification to prevent changing pageblock. > >If you give concrete justification so others isn't against on it, I am happy to > >do what you suggested. > > Well, MIGRATE_HIGHATOMIC is not listed in the fallbacks array at all, so we > are not supposed to steal from it in the first place. Stealing will only > happen due to races, which would be too costly to close, so we allow them > and expect to be rare. But we shouldn't allow them to break the accounting. > Fair enough. How about this? >>From 4a0b6a74ebf1af7f90720b0028da49e2e2a2b679 Mon Sep 17 00:00:00 2001 From: Minchan Kim Date: Thu, 6 Oct 2016 13:38:35 +0900 Subject: [PATCH] mm: don't steal highatomic pageblock In page freeing path, migratetype is racy so that a highorderatomic page could free into non-highorderatomic free list. If that page is allocated, VM can change the pageblock from higorderatomic to something. In that case, highatomic pageblock accounting is broken so it doesn't work(e.g., VM cannot reserve highorderatomic pageblocks any more although it doesn't reach 1% limit). So, this patch prohibits the changing from highatomic to other type. It's no problem because MIGRATE_HIGHATOMIC is not listed in fallback array so stealing will only happen due to unexpected races which is really rare. Also, such prohibiting keeps highatomic pageblock more longer so it would be better for highorderatomic page allocation. Signed-off-by: Minchan Kim --- mm/page_alloc.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 55ad0229ebf3..79853b258211 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2154,7 +2154,8 @@ __rmqueue_fallback(struct zone *zone, unsigned int order, int start_migratetype) page = list_first_entry(&area->free_list[fallback_mt], struct page, lru); - if (can_steal) + if (can_steal && + get_pageblock_migratetype(page) != MIGRATE_HIGHATOMIC) steal_suitable_fallback(zone, page, start_migratetype); /* Remove the page from the freelists */ @@ -2555,7 +2556,8 @@ int __isolate_free_page(struct page *page, unsigned int order) struct page *endpage = page + (1 << order) - 1; for (; page < endpage; page += pageblock_nr_pages) { int mt = get_pageblock_migratetype(page); - if (!is_migrate_isolate(mt) && !is_migrate_cma(mt)) + if (!is_migrate_isolate(mt) && !is_migrate_cma(mt) + && mt != MIGRATE_HIGHATOMIC) set_pageblock_migratetype(page, MIGRATE_MOVABLE); } -- 2.7.4