From: David Hildenbrand <david@redhat.com>
To: Mel Gorman <mgorman@suse.de>
Cc: Andrea Arcangeli <aarcange@redhat.com>,
Vlastimil Babka <vbabka@suse.cz>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, Qian Cai <cai@lca.pw>,
Michal Hocko <mhocko@kernel.org>,
linux-kernel@vger.kernel.org, Mike Rapoport <rppt@linux.ibm.com>,
Baoquan He <bhe@redhat.com>
Subject: Re: [PATCH 1/1] mm: compaction: avoid fast_isolate_around() to set pageblock_skip on reserved pages
Date: Wed, 25 Nov 2020 12:04:15 +0100 [thread overview]
Message-ID: <5f01bde6-fe31-9b0e-f288-06b82598a8b3@redhat.com> (raw)
In-Reply-To: <20201125103933.GM3306@suse.de>
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?
Assume your end of memory falls within a section - what would be the
right node/zone for such a memory hole at the end of the section? With
memory hotplug after such a hole, we can easily have multiple
nodes/zones spanning such a hole, unknown before hotplug.
IMHO, marking memory holes properly (as discussed) would be the cleanest
approach. For now, we use node/zone 0 + PageReserved - because memory
hotunplug (zone shrinking etc.) doesn't really care about ZONE_DMA.
>
>>>
>>> Whenever pfn_valid is true, it's better that the zoneid/nid is correct
>>> all times, otherwise if the second stage fails we end up in a bug with
>>> weird side effects.
>>
>> Memory holes with a valid memmap might not have a zone/nid. For now, skipping reserved pages should be good enough, no?
>>
>
> It would partially paper over the issue that setting the pageblock type
> based on a reserved page. I agree that compaction should not be returning
> pfns that are outside of the zone range because that is buggy in itself
> but valid struct pages should have valid information. I don't think we
> want to paper over that with unnecessary PageReserved checks.
Agreed as long as we can handle that issue using range checks.
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2020-11-25 11:04 UTC|newest]
Thread overview: 61+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-23 21:25 compaction: VM_BUG_ON_PAGE(!zone_spans_pfn(page_zone(page), pfn)) Qian Cai
2020-04-24 3:43 ` Baoquan He
2020-04-24 13:45 ` Qian Cai
2020-05-05 12:43 ` Baoquan He
2020-05-05 13:20 ` Qian Cai
2020-05-11 1:21 ` Baoquan He
2020-04-26 14:41 ` Mike Rapoport
2020-04-27 13:45 ` Qian Cai
2020-11-21 19:45 ` [PATCH 0/1] VM_BUG_ON_PAGE(!zone_spans_pfn) in set_pfnblock_flags_mask Andrea Arcangeli
2020-11-21 19:45 ` [PATCH 1/1] mm: compaction: avoid fast_isolate_around() to set pageblock_skip on reserved pages Andrea Arcangeli
2020-11-21 19:53 ` Andrea Arcangeli
2020-11-23 11:26 ` David Hildenbrand
2020-11-23 13:01 ` Vlastimil Babka
2020-11-24 13:32 ` Mel Gorman
2020-11-24 20:56 ` Andrea Arcangeli
2020-11-25 10:30 ` Mel Gorman
2020-11-25 17:59 ` Andrea Arcangeli
2020-11-26 10:47 ` Mel Gorman
2020-12-06 2:26 ` Andrea Arcangeli
2020-12-06 23:47 ` Mel Gorman
2020-11-25 5:34 ` Andrea Arcangeli
2020-11-25 6:45 ` David Hildenbrand
2020-11-25 8:51 ` Mike Rapoport
2020-11-25 10:39 ` Mel Gorman
2020-11-25 11:04 ` David Hildenbrand [this message]
2020-11-25 11:41 ` David Hildenbrand
2020-11-25 18:47 ` Andrea Arcangeli
2020-11-25 13:33 ` Mel Gorman
2020-11-25 13:41 ` David Hildenbrand
2020-11-25 18:28 ` Andrea Arcangeli
2020-11-25 19:27 ` David Hildenbrand
2020-11-25 20:41 ` Andrea Arcangeli
2020-11-25 21:13 ` David Hildenbrand
2020-11-25 21:04 ` Mike Rapoport
2020-11-25 21:38 ` Andrea Arcangeli
2020-11-26 9:36 ` Mike Rapoport
2020-11-26 10:05 ` David Hildenbrand
2020-11-26 17:46 ` Mike Rapoport
2020-11-29 12:32 ` Mike Rapoport
2020-12-02 0:44 ` Andrea Arcangeli
2020-12-02 17:39 ` Mike Rapoport
2020-12-03 6:23 ` Andrea Arcangeli
2020-12-03 10:51 ` Mike Rapoport
2020-12-03 17:31 ` Andrea Arcangeli
2020-12-06 8:09 ` Mike Rapoport
2020-11-26 18:15 ` Andrea Arcangeli
2020-11-26 18:29 ` Andrea Arcangeli
2020-11-26 19:44 ` Mike Rapoport
2020-11-26 20:30 ` Andrea Arcangeli
2020-11-26 21:03 ` Mike Rapoport
2020-11-26 19:21 ` Andrea Arcangeli
2020-11-25 12:08 ` Vlastimil Babka
2020-11-25 13:32 ` David Hildenbrand
2020-11-25 14:13 ` Mike Rapoport
2020-11-25 14:42 ` David Hildenbrand
2020-11-26 10:51 ` Mel Gorman
2020-11-25 19:14 ` Andrea Arcangeli
2020-11-25 19:01 ` Andrea Arcangeli
2020-11-25 19:33 ` David Hildenbrand
2020-11-26 3:40 ` Andrea Arcangeli
2020-11-26 10:43 ` Mike Rapoport
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