From: Vlastimil Babka <vbabka@suse.cz>
To: Andrea Arcangeli <aarcange@redhat.com>,
David Hildenbrand <david@redhat.com>
Cc: Mel Gorman <mgorman@suse.de>,
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 13:08:54 +0100 [thread overview]
Message-ID: <1c4c405b-52e0-cf6b-1f82-91a0a1e3dd53@suse.cz> (raw)
In-Reply-To: <X73s8fxDKPRD6wET@redhat.com>
On 11/25/20 6:34 AM, Andrea Arcangeli wrote:
> Hello,
>
> On Mon, Nov 23, 2020 at 02:01:16PM +0100, Vlastimil Babka wrote:
>> On 11/21/20 8:45 PM, Andrea Arcangeli wrote:
>> > A corollary issue was fixed in
>> > 39639000-39814fff : Unknown E820 type
>> >
>> > pfn 0x7a200 -> 0x7a200000 min_pfn hit non-RAM:
>> >
>> > 7a17b000-7a216fff : Unknown E820 type
>>
>> It would be nice to also provide a /proc/zoneinfo and how exactly the
>> "zone_spans_pfn" was violated. I assume we end up below zone's
>> start_pfn, but is it true?
>
> Agreed, I was about to grab that info along with all page struct
> around the pfn 0x7a200 and phys address 0x7a216fff.
>
> # grep -A1 E820 /proc/iomem
> 7a17b000-7a216fff : Unknown E820 type
> 7a217000-7bffffff : System RAM
>
> DMA zone_start_pfn 1 zone_end_pfn() 4096 contiguous 1
> DMA32 zone_start_pfn 4096 zone_end_pfn() 1048576 contiguous 0
> Normal zone_start_pfn 1048576 zone_end_pfn() 4715392 contiguous 1
> Movable zone_start_pfn 0 zone_end_pfn() 0 contiguous 0
So the above means that around the "Unknown E820 type" we have:
pfn 499712 - start of pageblock in ZONE_DMA32
pfn 500091 - start of the "Unknown E820 type" range
pfn 500224 - start of another pageblock
pfn 500246 - end of "Unknown E820 type"
So this is indeed not a zone boundary issue, but basically a hole not
aligned to pageblock boundary and really unexpected.
We have CONFIG_HOLES_IN_ZONE (that x86 doesn't set) for architectures
that do this, and even that config only affects pfn_valid_within(). But
here pfn_valid() is true, but the zone/node linkage is unexpected.
> However the real bug seems that reserved pages have a zero zone_id in
> the page->flags when it should have the real zone id/nid. The patch I
> sent earlier to validate highest would only be needed to deal with
> pfn_valid.
>
> 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);
>
> Even if it may not be it, at the light of how the reserved page
> zoneid/nid initialized went wrong, the above line like it's too flakey
> to stay.
>
> It'd be preferable if the pfn_valid fails and the
> pfn_to_section_nr(pfn) returns an invalid section for the intermediate
> step. Even better memset 0xff over the whole page struct until the
> second stage comes around.
>
> 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.
Yeah I guess it would be simpler if zoneid/nid was correct for
pfn_valid() pfns within a zone's range, even if they are reserved due
not not being really usable memory.
I don't think we want to introduce CONFIG_HOLES_IN_ZONE to x86. If the
chosen solution is to make this to a real hole, the hole should be
extended to MAX_ORDER_NR_PAGES aligned boundaries.
In any case, compaction code can't fix this with better range checks.
> Maybe it's not the above that left a zero zoneid though, I haven't
> tried to bisect it yet to look how the page->flags looked like on a
> older kernel that didn't seem to reproduce this crash, I'm just
> guessing.
>
> Thanks,
> Andrea
>
next prev parent reply other threads:[~2020-11-25 12:08 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
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 [this message]
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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