From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qk1-f199.google.com (mail-qk1-f199.google.com [209.85.222.199]) by kanga.kvack.org (Postfix) with ESMTP id A9ADC6B0006 for ; Wed, 14 Nov 2018 22:18:07 -0500 (EST) Received: by mail-qk1-f199.google.com with SMTP id w185so42883501qka.9 for ; Wed, 14 Nov 2018 19:18:07 -0800 (PST) Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id v127si12885113qkc.159.2018.11.14.19.18.06 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 14 Nov 2018 19:18:06 -0800 (PST) Date: Thu, 15 Nov 2018 11:18:01 +0800 From: Baoquan He Subject: Re: [PATCH] mm, memory_hotplug: check zone_movable in has_unmovable_pages Message-ID: <20181115031801.GJ2653@MiWiFi-R3L-srv> References: <20181106095524.14629-1-mhocko@kernel.org> <20181115031325.GI2653@MiWiFi-R3L-srv> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181115031325.GI2653@MiWiFi-R3L-srv> Sender: owner-linux-mm@kvack.org List-ID: To: Michal Hocko Cc: Andrew Morton , Oscar Salvador , linux-mm@kvack.org, LKML , Michal Hocko On 11/15/18 at 11:13am, Baoquan He wrote: > On 11/06/18 at 10:55am, Michal Hocko wrote: > > From: Michal Hocko > > > > Page state checks are racy. Under a heavy memory workload (e.g. stress > > -m 200 -t 2h) it is quite easy to hit a race window when the page is > > allocated but its state is not fully populated yet. A debugging patch to > > The original phenomenon is the value of /sys/devices/system/memory/memoryxxx/removable > is 0 on several memory blocks of hotpluggable node. And almost on each > hotpluggable node, there are one or several blocks which has this zero > value of removable attribute. It caused the hot removing failure always. > > And only cat /sys/devices/system/memory/memoryxxx/removable will trigger > the call trace. > > With this fix, all 'removable' of memory block on those hotpluggable > nodes are '1', and hotplug can succeed. Oh, by the way, hot removing/adding can always succeed when no memory pressure is added. The hot removing failure with high memory pressure has been raised in another thread. Thanks Baoquan > > > dump the struct page state shows > > : [ 476.575516] has_unmovable_pages: pfn:0x10dfec00, found:0x1, count:0x0 > > : [ 476.582103] page:ffffea0437fb0000 count:1 mapcount:1 mapping:ffff880e05239841 index:0x7f26e5000 compound_mapcount: 1 > > : [ 476.592645] flags: 0x5fffffc0090034(uptodate|lru|active|head|swapbacked) > > > > Note that the state has been checked for both PageLRU and PageSwapBacked > > already. Closing this race completely would require some sort of retry > > logic. This can be tricky and error prone (think of potential endless > > or long taking loops). > > > > Workaround this problem for movable zones at least. Such a zone should > > only contain movable pages. 15c30bc09085 ("mm, memory_hotplug: make > > has_unmovable_pages more robust") has told us that this is not strictly > > true though. Bootmem pages should be marked reserved though so we can > > move the original check after the PageReserved check. Pages from other > > zones are still prone to races but we even do not pretend that memory > > hotremove works for those so pre-mature failure doesn't hurt that much. > > > > Reported-and-tested-by: Baoquan He > > Acked-by: Baoquan He > > Fixes: "mm, memory_hotplug: make has_unmovable_pages more robust") > > Fixes: 15c30bc09085 "mm, memory_hotplug: make has_unmovable_pages more robust") > > > Signed-off-by: Michal Hocko > > --- > > > > Hi, > > this has been reported [1] and we have tried multiple things to address > > the issue. The only reliable way was to reintroduce the movable zone > > check into has_unmovable_pages. This time it should be safe also for > > the bug originally fixed by 15c30bc09085. > > > > [1] http://lkml.kernel.org/r/20181101091055.GA15166@MiWiFi-R3L-srv > > mm/page_alloc.c | 8 ++++++++ > > 1 file changed, 8 insertions(+) > > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > index 863d46da6586..c6d900ee4982 100644 > > --- a/mm/page_alloc.c > > +++ b/mm/page_alloc.c > > @@ -7788,6 +7788,14 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count, > > if (PageReserved(page)) > > goto unmovable; > > > > + /* > > + * If the zone is movable and we have ruled out all reserved > > + * pages then it should be reasonably safe to assume the rest > > + * is movable. > > + */ > > + if (zone_idx(zone) == ZONE_MOVABLE) > > + continue; > > + > > /* > > * Hugepages are not in LRU lists, but they're movable. > > * We need not scan over tail pages bacause we don't > > -- > > 2.19.1 > >