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=-6.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED 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 D02BAC07E85 for ; Tue, 11 Dec 2018 09:35:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 87FCE20849 for ; Tue, 11 Dec 2018 09:35:58 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 87FCE20849 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726137AbeLKJf5 (ORCPT ); Tue, 11 Dec 2018 04:35:57 -0500 Received: from mx1.redhat.com ([209.132.183.28]:50246 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726085AbeLKJf4 (ORCPT ); Tue, 11 Dec 2018 04:35:56 -0500 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id DCF0F308212D; Tue, 11 Dec 2018 09:35:55 +0000 (UTC) Received: from [10.36.117.115] (ovpn-117-115.ams2.redhat.com [10.36.117.115]) by smtp.corp.redhat.com (Postfix) with ESMTP id 3DDA7608F7; Tue, 11 Dec 2018 09:35:54 +0000 (UTC) Subject: Re: [PATCH] mm, memory_hotplug: Don't bail out in do_migrate_range prematurely To: Oscar Salvador , akpm@linux-foundation.org Cc: mhocko@suse.com, pasha.tatashin@soleen.com, dan.j.williams@gmail.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20181211085042.2696-1-osalvador@suse.de> From: David Hildenbrand Openpgp: preference=signencrypt Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.1 MIME-Version: 1.0 In-Reply-To: <20181211085042.2696-1-osalvador@suse.de> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.42]); Tue, 11 Dec 2018 09:35:55 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11.12.18 09:50, Oscar Salvador wrote: > do_migrate_ranges() takes a memory range and tries to isolate the > pages to put them into a list. > This list will be later on used in migrate_pages() to know > the pages we need to migrate. > > Currently, if we fail to isolate a single page, we put all already > isolated pages back to their LRU and we bail out from the function. > This is quite suboptimal, as this will force us to start over again > because scan_movable_pages will give us the same range. > If there is no chance that we can isolate that page, we will loop here > forever. > > Issue debugged in 4d0c7db96 ("hwpoison, memory_hotplug: allow hwpoisoned > pages to be offlined") has proved that. > During the debugging of that issue, it was noticed that if > do_migrate_ranges() fails to isolate a single page, we will > just discard the work we have done so far and bail out, which means > that scan_movable_pages() will find again the same set of pages. > > Instead, we can just skip the error, keep isolating as much pages > as possible and then proceed with the call to migrate_pages(). > This will allow us to do some work at least. > > There is no danger in the skipped pages to be lost, because > scan_movable_pages() will give us them as they could not > be isolated and therefore migrated. > > Although this patch has proved to be useful when dealing with > 4d0c7db96 because it allows us to move forward as long as the > page is not in LRU, we still need 4d0c7db96 > ("hwpoison, memory_hotplug: allow hwpoisoned pages to be offlined") > to handle the LRU case and the unmapping of the page if needed. > So, this is just a follow-up cleanup. So if I get it right the behavior of the function is now "If at least one page could be migrated, return 0. If no pages could be migrated, return an error." Don't we want that to be "If all pages could be migrated, return 0. If only a subset could be migrated, return -EAGAIN. If no pages could be migrated, return the causing error." So somehow remember if we had issues with one page and instead of reporting 0, report e.g. -EAGAIN? Meaning something like "If you get -EAGAIN, try again to get the real reason". > > Signed-off-by: Oscar Salvador > --- > mm/memory_hotplug.c | 19 +------------------ > 1 file changed, 1 insertion(+), 18 deletions(-) > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index 86ab673fc4e3..804d0280d2ab 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -1339,7 +1339,6 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn) > unsigned long pfn; > struct page *page; > int move_pages = NR_OFFLINE_AT_ONCE_PAGES; > - int not_managed = 0; > int ret = 0; > LIST_HEAD(source); > > @@ -1395,25 +1394,9 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn) > inc_node_page_state(page, NR_ISOLATED_ANON + > page_is_file_cache(page)); > > - } else { > - pr_warn("failed to isolate pfn %lx\n", pfn); > - dump_page(page, "isolation failed"); > - put_page(page); > - /* Because we don't have big zone->lock. we should > - check this again here. */ > - if (page_count(page)) { > - not_managed++; > - ret = -EBUSY; > - break; > - } > } > } > if (!list_empty(&source)) { > - if (not_managed) { > - putback_movable_pages(&source); > - goto out; > - } > - > /* Allocate a new page from the nearest neighbor node */ > ret = migrate_pages(&source, new_node_page, NULL, 0, > MIGRATE_SYNC, MR_MEMORY_HOTPLUG); > @@ -1426,7 +1409,7 @@ do_migrate_range(unsigned long start_pfn, unsigned long end_pfn) > putback_movable_pages(&source); > } > } > -out: > + > return ret; > } > > -- Thanks, David / dhildenb