From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f70.google.com (mail-ed1-f70.google.com [209.85.208.70]) by kanga.kvack.org (Postfix) with ESMTP id 8EB688E0001 for ; Wed, 19 Dec 2018 08:53:10 -0500 (EST) Received: by mail-ed1-f70.google.com with SMTP id d41so16193196eda.12 for ; Wed, 19 Dec 2018 05:53:10 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id b9sor10684428eda.20.2018.12.19.05.53.09 for (Google Transport Security); Wed, 19 Dec 2018 05:53:09 -0800 (PST) Date: Wed, 19 Dec 2018 13:53:07 +0000 From: Wei Yang Subject: Re: [PATCH v2] mm, page_isolation: remove drain_all_pages() in set_migratetype_isolate() Message-ID: <20181219135307.bjd6rckseczpfeae@master> Reply-To: Wei Yang References: <20181214023912.77474-1-richard.weiyang@gmail.com> <20181218204656.4297-1-richard.weiyang@gmail.com> <20181219095110.GB5758@dhcp22.suse.cz> <20181219095715.73x6hvmndyku2rec@d104.suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181219095715.73x6hvmndyku2rec@d104.suse.de> Sender: owner-linux-mm@kvack.org List-ID: To: Oscar Salvador Cc: Michal Hocko , Wei Yang , linux-mm@kvack.org, akpm@linux-foundation.org, david@redhat.com On Wed, Dec 19, 2018 at 10:57:19AM +0100, Oscar Salvador wrote: >On Wed, Dec 19, 2018 at 10:51:10AM +0100, Michal Hocko wrote: >> On Wed 19-12-18 04:46:56, Wei Yang wrote: >> > Below is a brief call flow for __offline_pages() and >> > alloc_contig_range(): >> > >> > __offline_pages()/alloc_contig_range() >> > start_isolate_page_range() >> > set_migratetype_isolate() >> > drain_all_pages() >> > drain_all_pages() >> > >> > Current logic is: isolate and drain pcp list for each pageblock and >> > drain pcp list again. This is not necessary and we could just drain pcp >> > list once after isolate this whole range. >> > >> > The reason is start_isolate_page_range() will set the migrate type of >> > a range to MIGRATE_ISOLATE. After doing so, this range will never be >> > allocated from Buddy, neither to a real user nor to pcp list. >> >> But it is important to note that those pages still can be allocated from >> the pcp lists until we do drain_all_pages(). > >I had the same fear, but then I saw that move_freepages_block()->move_freepages() moves >the pages to a new list: > ><-- >list_move(&page->lru, > &zone->free_area[order].free_list[migratetype]); >--> > > >But looking at it again, I see that this is only for BuddyPages, so I guess >that pcp-pages do not really get unlinked, so we could still allocate them. Well, I think you are right. But with this in mind, current code looks buggy. Between has_unmovable_pages() and drain_all_pages(), others still could allocate pages on pcp list, right? This means we thought we have isolated the range, but not. So even we do drain_all_pages(), we still missed some pages in this range. > >Uhmf, I missed that. > >-- >Oscar Salvador >SUSE L3 -- Wei Yang Help you, Help me