From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_NEOMUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E5B8DC10F00 for ; Tue, 12 Mar 2019 15:35:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C2250214AF for ; Tue, 12 Mar 2019 15:35:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726792AbfCLPfI (ORCPT ); Tue, 12 Mar 2019 11:35:08 -0400 Received: from nat.nue.novell.com ([195.135.221.2]:46023 "EHLO suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726218AbfCLPfI (ORCPT ); Tue, 12 Mar 2019 11:35:08 -0400 Received: by suse.de (Postfix, from userid 1000) id 87303453F; Tue, 12 Mar 2019 16:35:06 +0100 (CET) Date: Tue, 12 Mar 2019 16:35:06 +0100 From: Oscar Salvador To: Qian Cai Cc: akpm@linux-foundation.org, mhocko@suse.com, vbabka@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RESEND PATCH] mm/hotplug: don't reset pagetype flags for offline Message-ID: <20190312153458.qvmrblg3pnokgx4d@d104.suse.de> References: <20190310200102.88014-1-cai@lca.pw> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190310200102.88014-1-cai@lca.pw> User-Agent: NeoMutt/20170421 (1.8.2) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Mar 10, 2019 at 04:01:02PM -0400, Qian Cai wrote: > The commit f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded > memory to zones until online") introduced move_pfn_range_to_zone() which > calls memmap_init_zone() during onlining a memory block. > memmap_init_zone() will reset pagetype flags and makes migrate type to > be MOVABLE. > > However, in __offline_pages(), it also call undo_isolate_page_range() > after offline_isolated_pages() to do the same thing. Due to > the commit 2ce13640b3f4 ("mm: __first_valid_page skip over offline > pages") changed __first_valid_page() to skip offline pages, > undo_isolate_page_range() here just waste CPU cycles looping around the > offlining PFN range while doing nothing, because __first_valid_page() > will return NULL as offline_isolated_pages() has already marked all > memory sections within the pfn range as offline via > offline_mem_sections(). > > Also, after calling the "useless" undo_isolate_page_range() here, it > reaches the point of no returning by notifying MEM_OFFLINE. Those pages > will be marked as MIGRATE_MOVABLE again once onlining. In addition, fix > an incorrect comment along the way. > > Signed-off-by: Qian Cai Reviewed-by: Oscar Salvador One thing I noticed when looking at start_isolate_page_range and undo_isolate_page_range functions, is that start_isolate_page_range increments the number of isolated pageblocks, while undo_isolate_page_range does the counter part. Since undo_isolate_page_range is really never called during offlining, we leave zone->nr_isolate_pageblock with a stale value. I __think__ this does not matter much. We only get to check whether a zone got isolated pageblocks in has_isolate_pageblock(), and this is called from: free_one_page free_pcppages_bulk __free_one_page With a quick glance, the only difference in has_isolate_pageblock() returning true or false, seems to be that those functions perform some extra checks in case the zone reports to have isolated pageblocks. I wonder if we should set nr_isolate_pageblock back to its original value before start_isolate_page_range. > --- > mm/memory_hotplug.c | 2 -- > mm/sparse.c | 2 +- > 2 files changed, 1 insertion(+), 3 deletions(-) > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index 6b05576fb4ec..46017040b2f8 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -1655,8 +1655,6 @@ static int __ref __offline_pages(unsigned long start_pfn, > /* Ok, all of our target is isolated. > We cannot do rollback at this point. */ > offline_isolated_pages(start_pfn, end_pfn); > - /* reset pagetype flags and makes migrate type to be MOVABLE */ > - undo_isolate_page_range(start_pfn, end_pfn, MIGRATE_MOVABLE); > /* removal success */ > adjust_managed_page_count(pfn_to_page(start_pfn), -offlined_pages); > zone->present_pages -= offlined_pages; > diff --git a/mm/sparse.c b/mm/sparse.c > index 77a0554fa5bd..b3771f35a0ed 100644 > --- a/mm/sparse.c > +++ b/mm/sparse.c > @@ -556,7 +556,7 @@ void online_mem_sections(unsigned long start_pfn, unsigned long end_pfn) > } > > #ifdef CONFIG_MEMORY_HOTREMOVE > -/* Mark all memory sections within the pfn range as online */ > +/* Mark all memory sections within the pfn range as offline */ > void offline_mem_sections(unsigned long start_pfn, unsigned long end_pfn) > { > unsigned long pfn; > -- > 2.17.2 (Apple Git-113) > -- Oscar Salvador SUSE L3