From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f69.google.com (mail-ed1-f69.google.com [209.85.208.69]) by kanga.kvack.org (Postfix) with ESMTP id BDBB48E0001 for ; Wed, 19 Dec 2018 09:33:30 -0500 (EST) Received: by mail-ed1-f69.google.com with SMTP id e17so16433885edr.7 for ; Wed, 19 Dec 2018 06:33:30 -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 s23-v6sor4919553eju.43.2018.12.19.06.33.29 for (Google Transport Security); Wed, 19 Dec 2018 06:33:29 -0800 (PST) Date: Wed, 19 Dec 2018 14:33:27 +0000 From: Wei Yang Subject: Re: [PATCH v2] mm, page_isolation: remove drain_all_pages() in set_migratetype_isolate() Message-ID: <20181219143327.wdsufbn2oh6ygnne@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> <20181219135307.bjd6rckseczpfeae@master> <20181219141343.GN5758@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181219141343.GN5758@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Wei Yang , Oscar Salvador , linux-mm@kvack.org, akpm@linux-foundation.org, david@redhat.com On Wed, Dec 19, 2018 at 03:13:43PM +0100, Michal Hocko wrote: >On Wed 19-12-18 13:53:07, Wei Yang wrote: >> 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. > >THere is no guarantee in that regards and I believe there is also no >demand for such a strong semantic. Or I do not see it at least. If there is no demand for this, allocating page before drain_all_pages() is reasonable. The time gap between isolating page and drain_all_pages is fine. Then I am confused about the objection to this patch. Finally, we drain all the pages in pcp list and the range is isolated. >-- >Michal Hocko >SUSE Labs -- Wei Yang Help you, Help me