From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg1-f199.google.com (mail-pg1-f199.google.com [209.85.215.199]) by kanga.kvack.org (Postfix) with ESMTP id CF55A8E0001 for ; Wed, 19 Dec 2018 04:51:14 -0500 (EST) Received: by mail-pg1-f199.google.com with SMTP id t26so16192296pgu.18 for ; Wed, 19 Dec 2018 01:51:14 -0800 (PST) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id u5si15035172plj.129.2018.12.19.01.51.13 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 19 Dec 2018 01:51:13 -0800 (PST) Date: Wed, 19 Dec 2018 10:51:10 +0100 From: Michal Hocko Subject: Re: [PATCH v2] mm, page_isolation: remove drain_all_pages() in set_migratetype_isolate() Message-ID: <20181219095110.GB5758@dhcp22.suse.cz> References: <20181214023912.77474-1-richard.weiyang@gmail.com> <20181218204656.4297-1-richard.weiyang@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181218204656.4297-1-richard.weiyang@gmail.com> Sender: owner-linux-mm@kvack.org List-ID: To: Wei Yang Cc: linux-mm@kvack.org, akpm@linux-foundation.org, osalvador@suse.de, david@redhat.com 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 prevent start_isolate_page_range to work on multiple zones? At least contiguous allocator can do that in principle. So no I do not like this patch, it is not an improvement. -- Michal Hocko SUSE Labs