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Mon, 22 Jun 2020 04:43:21 -0400 X-MC-Unique: IYEsLOnOMuCXNbdsJ1I1dg-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 32388835B40; Mon, 22 Jun 2020 08:43:19 +0000 (UTC) Received: from [10.36.113.213] (ovpn-113-213.ams2.redhat.com [10.36.113.213]) by smtp.corp.redhat.com (Postfix) with ESMTP id 5B42C5C221; Mon, 22 Jun 2020 08:43:13 +0000 (UTC) Subject: Re: [PATCH v2 1/3] mm/shuffle: don't move pages between zones and don't read garbage memmaps To: Wei Yang Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Michal Hocko , stable@vger.kernel.org, Andrew Morton , Johannes Weiner , Minchan Kim , Huang Ying , Wei Yang , Mel Gorman References: <20200619125923.22602-1-david@redhat.com> <20200619125923.22602-2-david@redhat.com> <20200622082635.GA93552@L-31X9LVDL-1304.local> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <20200622082635.GA93552@L-31X9LVDL-1304.local> Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Rspamd-Queue-Id: 0FD6218038E60 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam03 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 22.06.20 10:26, Wei Yang wrote: > On Fri, Jun 19, 2020 at 02:59:20PM +0200, David Hildenbrand wrote: >> Especially with memory hotplug, we can have offline sections (with a >> garbage memmap) and overlapping zones. We have to make sure to only >> touch initialized memmaps (online sections managed by the buddy) and t= hat >> the zone matches, to not move pages between zones. >> >> To test if this can actually happen, I added a simple >> BUG_ON(page_zone(page_i) !=3D page_zone(page_j)); >> right before the swap. When hotplugging a 256M DIMM to a 4G x86-64 VM = and >> onlining the first memory block "online_movable" and the second memory >> block "online_kernel", it will trigger the BUG, as both zones (NORMAL >> and MOVABLE) overlap. >> >> This might result in all kinds of weird situations (e.g., double >> allocations, list corruptions, unmovable allocations ending up in the >> movable zone). >> >> Fixes: e900a918b098 ("mm: shuffle initial free memory to improve memor= y-side-cache utilization") >> Acked-by: Michal Hocko >> Cc: stable@vger.kernel.org # v5.2+ >> Cc: Andrew Morton >> Cc: Johannes Weiner >> Cc: Michal Hocko >> Cc: Minchan Kim >> Cc: Huang Ying >> Cc: Wei Yang >> Cc: Mel Gorman >> Signed-off-by: David Hildenbrand >> --- >> mm/shuffle.c | 18 +++++++++--------- >> 1 file changed, 9 insertions(+), 9 deletions(-) >> >> diff --git a/mm/shuffle.c b/mm/shuffle.c >> index 44406d9977c77..dd13ab851b3ee 100644 >> --- a/mm/shuffle.c >> +++ b/mm/shuffle.c >> @@ -58,25 +58,25 @@ module_param_call(shuffle, shuffle_store, shuffle_= show, &shuffle_param, 0400); >> * For two pages to be swapped in the shuffle, they must be free (on a >> * 'free_area' lru), have the same order, and have the same migratetyp= e. >> */ >> -static struct page * __meminit shuffle_valid_page(unsigned long pfn, = int order) >> +static struct page * __meminit shuffle_valid_page(struct zone *zone, >> + unsigned long pfn, int order) >> { >> - struct page *page; >> + struct page *page =3D pfn_to_online_page(pfn); >=20 > Hi, David and Dan, >=20 > One thing I want to confirm here is we won't have partially online sect= ion, > right? We can add a sub-section to system, but we won't manage it by bu= ddy. Hi, there is still a BUG with sub-section hot-add (devmem), which broke pfn_to_online_page() in corner cases (especially, see the description in include/linux/mmzone.h). We can have a boot-memory section partially populated and marked online. Then, we can hot-add devmem, marking the remaining pfns valid - and as the section is maked online, also as online= . This is, however, a different problem to solve and affects most other pfn walkers as well. The "if (page_zone(page) !=3D zone)" checks guards u= s from most harm, as the devmem zone won't match. Thanks! --=20 Thanks, David / dhildenb