Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753436AbdIDIWZ (ORCPT ); Mon, 4 Sep 2017 04:22:25 -0400 Received: from mail-wm0-f68.google.com ([74.125.82.68]:36692 "EHLO mail-wm0-f68.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753345AbdIDIV6 (ORCPT ); Mon, 4 Sep 2017 04:21:58 -0400 X-Google-Smtp-Source: ADKCNb5Glf+Ut6v6nr4P8a8TpU6WVsbedEvsSgGqKId31lafI3UKSEd+rdVVuPN9YVAXHhz4JB+bcw== From: Michal Hocko To: Andrew Morton Cc: KAMEZAWA Hiroyuki , Reza Arbab , Yasuaki Ishimatsu , qiuxishi@huawei.com, Igor Mammedov , Vitaly Kuznetsov , , LKML , Michal Hocko Subject: [PATCH 1/2] mm, memory_hotplug: do not fail offlining too early Date: Mon, 4 Sep 2017 10:21:47 +0200 Message-Id: <20170904082148.23131-2-mhocko@kernel.org> X-Mailer: git-send-email 2.14.1 In-Reply-To: <20170904082148.23131-1-mhocko@kernel.org> References: <20170904082148.23131-1-mhocko@kernel.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3831 Lines: 114 From: Michal Hocko Memory offlining can fail just too eagerly under a heavy memory pressure. [ 5410.336792] page:ffffea22a646bd00 count:255 mapcount:252 mapping:ffff88ff926c9f38 index:0x3 [ 5410.336809] flags: 0x9855fe40010048(uptodate|active|mappedtodisk) [ 5410.336811] page dumped because: isolation failed [ 5410.336813] page->mem_cgroup:ffff8801cd662000 [ 5420.655030] memory offlining [mem 0x18b580000000-0x18b5ffffffff] failed Isolation has failed here because the page is not on LRU. Most probably because it was on the pcp LRU cache or it has been removed from the LRU already but it hasn't been freed yet. In both cases the page doesn't look non-migrable so retrying more makes sense. __offline_pages seems rather cluttered when it comes to the retry logic. We have 5 retries at maximum and a timeout. We could argue whether the timeout makes sense but failing just because of a race when somebody isoltes a page from LRU or puts it on a pcp LRU lists is just wrong. It only takes it to race with a process which unmaps some pages and remove them from the LRU list and we can fail the whole offline because of something that is a temporary condition and actually not harmful for the offline. Please note that unmovable pages should be already excluded during start_isolate_page_range. Fix this by removing the max retry count and only rely on the timeout resp. interruption by a signal from the userspace. Also retry rather than fail when check_pages_isolated sees some !free pages because those could be a result of the race as well. Signed-off-by: Michal Hocko --- mm/memory_hotplug.c | 40 ++++++++++------------------------------ 1 file changed, 10 insertions(+), 30 deletions(-) diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index 459bbc182d10..c9dcbe6d2ac6 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -1597,7 +1597,7 @@ static int __ref __offline_pages(unsigned long start_pfn, { unsigned long pfn, nr_pages, expire; long offlined_pages; - int ret, drain, retry_max, node; + int ret, node; unsigned long flags; unsigned long valid_start, valid_end; struct zone *zone; @@ -1634,43 +1634,25 @@ static int __ref __offline_pages(unsigned long start_pfn, pfn = start_pfn; expire = jiffies + timeout; - drain = 0; - retry_max = 5; repeat: /* start memory hot removal */ - ret = -EAGAIN; + ret = -EBUSY; if (time_after(jiffies, expire)) goto failed_removal; ret = -EINTR; if (signal_pending(current)) goto failed_removal; - ret = 0; - if (drain) { - lru_add_drain_all_cpuslocked(); - cond_resched(); - drain_all_pages(zone); - } + + cond_resched(); + lru_add_drain_all_cpuslocked(); + drain_all_pages(zone); pfn = scan_movable_pages(start_pfn, end_pfn); if (pfn) { /* We have movable pages */ ret = do_migrate_range(pfn, end_pfn); - if (!ret) { - drain = 1; - goto repeat; - } else { - if (ret < 0) - if (--retry_max == 0) - goto failed_removal; - yield(); - drain = 1; - goto repeat; - } + goto repeat; } - /* drain all zone's lru pagevec, this is asynchronous... */ - lru_add_drain_all_cpuslocked(); - yield(); - /* drain pcp pages, this is synchronous. */ - drain_all_pages(zone); + /* * dissolve free hugepages in the memory block before doing offlining * actually in order to make hugetlbfs's object counting consistent. @@ -1680,10 +1662,8 @@ static int __ref __offline_pages(unsigned long start_pfn, goto failed_removal; /* check again */ offlined_pages = check_pages_isolated(start_pfn, end_pfn); - if (offlined_pages < 0) { - ret = -EBUSY; - goto failed_removal; - } + if (offlined_pages < 0) + goto repeat; pr_info("Offlined Pages %ld\n", offlined_pages); /* Ok, all of our target is isolated. We cannot do rollback at this point. */ -- 2.14.1