From: David Hildenbrand <david@redhat.com>
To: Vlastimil Babka <vbabka@suse.cz>, Zi Yan <ziy@nvidia.com>,
linux-mm@kvack.org
Cc: Matthew Wilcox <willy@infradead.org>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
Mike Kravetz <mike.kravetz@oracle.com>,
Michal Hocko <mhocko@kernel.org>,
John Hubbard <jhubbard@nvidia.com>,
linux-kernel@vger.kernel.org, Mike Rapoport <rppt@linux.ibm.com>
Subject: Re: [RFC PATCH 00/15] Make MAX_ORDER adjustable as a kernel boot time parameter.
Date: Fri, 6 Aug 2021 18:16:41 +0200 [thread overview]
Message-ID: <72b317e5-c78a-f0bc-fe69-f82261ec252e@redhat.com> (raw)
In-Reply-To: <40982106-0eee-4e62-7ce0-c4787b0afac4@suse.cz>
On 06.08.21 17:36, Vlastimil Babka wrote:
> On 8/5/21 9:02 PM, Zi Yan wrote:
>> From: Zi Yan <ziy@nvidia.com>
>
>> Patch 3 restores the pfn_valid_within() check when buddy allocator can merge
>> pages across memory sections. The check was removed when ARM64 gets rid of holes
>> in zones, but holes can appear in zones again after this patchset.
>
> To me that's most unwelcome resurrection. I kinda missed it was going away and
> now I can't even rejoice? I assume the systems that will be bumping max_order
> have a lot of memory. Are they going to have many holes? What if we just
> sacrificed the memory that would have a hole and don't add it to buddy at all?
I think the old implementation was just horrible and the description we
have here still suffers from that old crap: "but holes can appear in
zones again". No, it's not related to holes in zones at all. We can have
MAX_ORDER -1 pages that are partially a hole.
And to be precise, "hole" here means "there is no memmap" and not "there
is a hole but it has a valid memmap".
But IIRC, we now have under SPARSEMEM always a complete memmap for a
complete memory sections (when talking about system RAM, ZONE_DEVICE is
different but we don't really care for now I think).
So instead of introducing what we had before, I think we should look
into something that doesn't confuse each person that stumbles over it
out there. What does pfn_valid_within() even mean in the new context?
pfn_valid() is most probably no longer what we really want, as we're
dealing with multiple sections that might be online or offline; in the
old world, this was different, as a MAX_ORDER -1 page was completely
contained in a memory section that was either online or offline.
I'd imagine something that expresses something different in the context
of sparsemem:
"Some page orders, such as MAX_ORDER -1, might span multiple memory
sections. Each memory section has a completely valid memmap if online.
Memory sections might either be completely online or completely offline.
pfn_to_online_page() might succeed on one part of a MAX_ORDER - 1 page,
but not on another part. But it will certainly be consistent within one
memory section."
Further, as we know that MAX_ORDER -1 and memory sections are a power of
two, we can actually do a binary search to identify boundaries, instead
of having to check each and every page in the range.
Is what I describe the actual reason why we introduce pfn_valid_within()
? (and might better introduce something new, with a better fitting name?)
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2021-08-06 16:16 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-05 19:02 [RFC PATCH 00/15] Make MAX_ORDER adjustable as a kernel boot time parameter Zi Yan
2021-08-05 19:02 ` [RFC PATCH 01/15] arch: x86: remove MAX_ORDER exceeding SECTION_SIZE check for 32bit vdso Zi Yan
2021-08-05 19:02 ` [RFC PATCH 02/15] arch: mm: rename FORCE_MAX_ZONEORDER to ARCH_FORCE_MAX_ORDER Zi Yan
2021-08-05 19:02 ` [RFC PATCH 03/15] mm: check pfn validity when buddy allocator can merge pages across mem sections Zi Yan
2021-08-05 19:02 ` [RFC PATCH 04/15] mm: prevent pageblock size being larger than section size Zi Yan
2021-08-05 19:02 ` [RFC PATCH 05/15] mm/memory_hotplug: online pages at " Zi Yan
2021-08-05 19:02 ` [RFC PATCH 06/15] mm: use PAGES_PER_SECTION instead for mem_map_offset/next() Zi Yan
2021-08-05 19:02 ` [RFC PATCH 07/15] mm: hugetlb: use PAGES_PER_SECTION to check mem_map discontiguity Zi Yan
2021-08-05 19:02 ` [RFC PATCH 08/15] fs: proc: use PAGES_PER_SECTION for page offline checking period Zi Yan
2021-08-07 10:32 ` Mike Rapoport
2021-08-09 15:45 ` [RFC PATCH 08/15] " Zi Yan
2021-08-05 19:02 ` [RFC PATCH 09/15] virtio: virtio_mem: use PAGES_PER_SECTION instead of MAX_ORDER_NR_PAGES Zi Yan
2021-08-09 7:35 ` David Hildenbrand
2021-08-05 19:02 ` [RFC PATCH 10/15] virtio: virtio_balloon: " Zi Yan
2021-08-09 7:42 ` David Hildenbrand
2021-08-05 19:02 ` [RFC PATCH 11/15] mm/page_reporting: report pages at section size instead of MAX_ORDER Zi Yan
2021-08-09 7:25 ` David Hildenbrand
2021-08-09 14:12 ` Alexander Duyck
2021-08-09 15:08 ` Zi Yan
2021-08-09 16:51 ` Alexander Duyck
2021-08-09 14:08 ` Alexander Duyck
2021-08-05 19:02 ` [RFC PATCH 12/15] mm: Make MAX_ORDER of buddy allocator configurable via Kconfig SET_MAX_ORDER Zi Yan
2021-08-06 15:16 ` Vlastimil Babka
2021-08-06 15:23 ` Zi Yan
2021-08-05 19:02 ` [RFC PATCH 13/15] mm: convert MAX_ORDER sized static arrays to dynamic ones Zi Yan
2021-08-05 19:16 ` Christian König
2021-08-05 19:58 ` Zi Yan
2021-08-06 9:37 ` Christian König
2021-08-06 14:00 ` Zi Yan
2021-08-05 19:02 ` [RFC PATCH 14/15] mm: introduce MIN_MAX_ORDER to replace MAX_ORDER as compile time constant Zi Yan
2021-08-08 8:23 ` Mike Rapoport
2021-08-09 15:35 ` Zi Yan
2021-08-05 19:02 ` [RFC PATCH 15/15] mm: make MAX_ORDER a kernel boot time parameter Zi Yan
2021-08-06 15:36 ` [RFC PATCH 00/15] Make MAX_ORDER adjustable as " Vlastimil Babka
2021-08-06 16:16 ` David Hildenbrand [this message]
2021-08-06 16:54 ` Vlastimil Babka
2021-08-06 17:08 ` David Hildenbrand
2021-08-06 18:24 ` Zi Yan
2021-08-09 7:20 ` David Hildenbrand
2021-08-08 7:41 ` Mike Rapoport
2021-08-06 16:32 ` Vlastimil Babka
2021-08-06 17:19 ` Zi Yan
2021-08-06 20:27 ` Hugh Dickins
2021-08-06 21:26 ` Zi Yan
2021-08-09 4:04 ` Hugh Dickins
2021-08-07 1:10 ` Matthew Wilcox
2021-08-07 21:23 ` Matthew Wilcox
2021-08-09 4:29 ` Hugh Dickins
2021-08-09 11:22 ` Matthew Wilcox
2021-08-09 7:41 ` David Hildenbrand
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