From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ed1-f71.google.com (mail-ed1-f71.google.com [209.85.208.71]) by kanga.kvack.org (Postfix) with ESMTP id 8015A8E0001 for ; Wed, 19 Dec 2018 08:56:38 -0500 (EST) Received: by mail-ed1-f71.google.com with SMTP id i55so16437970ede.14 for ; Wed, 19 Dec 2018 05:56:38 -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 cc25-v6sor4890101ejb.20.2018.12.19.05.56.37 for (Google Transport Security); Wed, 19 Dec 2018 05:56:37 -0800 (PST) Date: Wed, 19 Dec 2018 13:56:35 +0000 From: Wei Yang Subject: Re: [PATCH v2] mm, page_isolation: remove drain_all_pages() in set_migratetype_isolate() Message-ID: <20181219135635.yloh2sn4uskzpy7g@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> <20181219132934.65vymftfgd2atcxa@master> <20181219134056.GL5758@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181219134056.GL5758@dhcp22.suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Wei Yang , linux-mm@kvack.org, akpm@linux-foundation.org, osalvador@suse.de, david@redhat.com On Wed, Dec 19, 2018 at 02:40:56PM +0100, Michal Hocko wrote: >On Wed 19-12-18 13:29:34, Wei Yang 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(). >> > >> >One thing that I really do not like about this patch (and I believe I >> >have mentioned that previously) that you rely on callers to do the right >> >thing. The proper fix would be to do the draining in >> >start_isolate_page_range and remove them from callers. Also what does >> >> Well, I don't really understand this meaning previously. >> >> So you prefer set_migratetype_isolate() do the drain instead of the >> caller (__offline_pages) do the drain. Is my understanding correct? > >Either set_migratetype_isolate or start_isolate_page_range. The later >only if this is guaranteed that we cannot intemix zones in the range. > >> >prevent start_isolate_page_range to work on multiple zones? At least >> >contiguous allocator can do that in principle. >> >> As the comment mentioned, in current implementation the range must be in >> one zone. > >I do not see anything like that documented for set_migratetype_isolate. The comment is not on set_migratetype_isolate, but for its two (grandparent) callers: __offline_pages alloc_contig_range >-- >Michal Hocko >SUSE Labs -- Wei Yang Help you, Help me