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 12E2E8E00AE for ; Fri, 4 Jan 2019 10:17:41 -0500 (EST) Received: by mail-ed1-f70.google.com with SMTP id b3so35329719edi.0 for ; Fri, 04 Jan 2019 07:17:41 -0800 (PST) Received: from mx1.suse.de (mx2.suse.de. [195.135.220.15]) by mx.google.com with ESMTPS id d1si6644499edr.19.2019.01.04.07.17.39 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 04 Jan 2019 07:17:39 -0800 (PST) Date: Fri, 4 Jan 2019 16:17:37 +0100 From: Michal Hocko Subject: Re: [PATCH v3] mm/page_owner: fix for deferred struct page init Message-ID: <20190104151737.GT31793@dhcp22.suse.cz> References: <20190103115114.GL31793@dhcp22.suse.cz> <20190103165927.GU31793@dhcp22.suse.cz> <5d8f3a98-a954-c8ab-83d9-2f94c614f268@lca.pw> <20190103190715.GZ31793@dhcp22.suse.cz> <62e96e34-7ea9-491a-b5b6-4828da980d48@lca.pw> <20190103202235.GE31793@dhcp22.suse.cz> <20190104130906.GO31793@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Qian Cai Cc: akpm@linux-foundation.org, Pavel.Tatashin@microsoft.com, mingo@kernel.org, mgorman@techsingularity.net, iamjoonsoo.kim@lge.com, tglx@linutronix.de, linux-mm@kvack.org, linux-kernel@vger.kernel.org On Fri 04-01-19 10:01:40, Qian Cai wrote: > On 1/4/19 8:09 AM, Michal Hocko wrote: > >> Here is the number without DEFERRED_STRUCT_PAGE_INIT. > >> > >> == page_ext_init() after page_alloc_init_late() == > >> Node 0, zone DMA: page owner found early allocated 0 pages > >> Node 0, zone DMA32: page owner found early allocated 7009 pages > >> Node 0, zone Normal: page owner found early allocated 85827 pages > >> Node 4, zone Normal: page owner found early allocated 75063 pages > >> > >> == page_ext_init() before kmemleak_init() == > >> Node 0, zone DMA: page owner found early allocated 0 pages > >> Node 0, zone DMA32: page owner found early allocated 6654 pages > >> Node 0, zone Normal: page owner found early allocated 41907 pages > >> Node 4, zone Normal: page owner found early allocated 41356 pages > >> > >> So, it told us that it will miss tens of thousands of early page allocation call > >> sites. > > > > This is an answer for the first part of the question (how much). The > > second is _do_we_care_? > > Well, the purpose of this simple "ugly" ifdef is to avoid a regression for the > existing page_owner users with DEFERRED_STRUCT_PAGE_INIT deselected that would > start to miss tens of thousands early page allocation call sites. I am pretty sure we will hear about that when that happens. And act accordingly. > The other option I can think of to not hurt your eyes is to rewrite the whole > page_ext_init(), init_page_owner(), init_debug_guardpage() to use all early > functions, so it can work in both with DEFERRED_STRUCT_PAGE_INIT=y and without. > However, I have a hard-time to convince myself it is a sensible thing to do. Or simply make the page_owner initialization only touch the already initialized memory. Have you explored that option as well? Look, I am trying to push for a clean solution. Hacks I have seen so far are not convincing. You have identified a regression and as such I would consider the most straightforward to revert the buggy commit. If you want to improve the situation then I would suggest to think about something that is more robust than ifdefed hacks. It might be more work but it also might be a better thing long term. If you think I am asking too much then you are free to ignore my opinion. I am not a maintainer of the page_owner code. -- Michal Hocko SUSE Labs