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Wed, 25 Nov 2020 18:47:25 +0000 (UTC) Received: from mail (ovpn-112-118.rdu2.redhat.com [10.10.112.118]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 417525D71B; Wed, 25 Nov 2020 18:47:22 +0000 (UTC) Date: Wed, 25 Nov 2020 13:47:21 -0500 From: Andrea Arcangeli To: David Hildenbrand Cc: Mel Gorman , Vlastimil Babka , Andrew Morton , linux-mm@kvack.org, Qian Cai , Michal Hocko , linux-kernel@vger.kernel.org, Mike Rapoport , Baoquan He Subject: Re: [PATCH 1/1] mm: compaction: avoid fast_isolate_around() to set pageblock_skip on reserved pages Message-ID: References: <35F8AADA-6CAA-4BD6-A4CF-6F29B3F402A4@redhat.com> <20201125103933.GM3306@suse.de> <5f01bde6-fe31-9b0e-f288-06b82598a8b3@redhat.com> <33612969-92a1-6c49-a2e0-3a95715b1e7f@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <33612969-92a1-6c49-a2e0-3a95715b1e7f@redhat.com> User-Agent: Mutt/2.0.2 (2020-11-20) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 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 Wed, Nov 25, 2020 at 12:41:55PM +0100, David Hildenbrand wrote: > On 25.11.20 12:04, David Hildenbrand wrote: > > On 25.11.20 11:39, Mel Gorman wrote: > >> On Wed, Nov 25, 2020 at 07:45:30AM +0100, David Hildenbrand wrote: > >>>> Something must have changed more recently than v5.1 that caused the > >>>> zoneid of reserved pages to be wrong, a possible candidate for the > >>>> real would be this change below: > >>>> > >>>> + __init_single_page(pfn_to_page(pfn), pfn, 0, 0); > >>>> > >>> > >>> Before that change, the memmap of memory holes were only zeroed out. So the zones/nid was 0, however, pages were not reserved and had a refcount of zero - resulting in other issues. > >>> > >>> Most pfn walkers shouldn???t mess with reserved pages and simply skip them. That would be the right fix here. > >>> > >> > >> Ordinarily yes, pfn walkers should not care about reserved pages but it's > >> still surprising that the node/zone linkages would be wrong for memory > >> holes. If they are in the middle of a zone, it means that a hole with > >> valid struct pages could be mistaken for overlapping nodes (if the hole > >> was in node 1 for example) or overlapping zones which is just broken. > > > > I agree within zones - but AFAIU, the issue is reserved memory between > > zones, right? > > Double checking, I was confused. This applies also to memory holes > within zones in x86. Yes this is a memory hole within the DMA32 zone. Still why there should be any difference? As long as a page struct exists it's in a well defined mem_map array which comes for one and only one zoneid/nid combination. So what would be the benefit of treating memory holes within zones or in between zones differently and leave one or the other with a zoneid/nid uninitialized?