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From:   Zi Yan <ziy@nvidia.com>
To:     Vlastimil Babka <vbabka@suse.cz>
Cc:     David Hildenbrand <david@redhat.com>, linux-mm@kvack.org,
        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
Subject: Re: [RFC PATCH 00/15] Make MAX_ORDER adjustable as a kernel boot time parameter.
Date:   Fri, 06 Aug 2021 13:19:11 -0400
Message-ID: <F34DBD0A-22DE-4CF2-B784-BBDD80A8E85A@nvidia.com>
In-Reply-To: <0d374eed-cc52-a656-b338-1156782bdf7e@suse.cz>
References: <20210805190253.2795604-1-zi.yan@sent.com>
 <0d374eed-cc52-a656-b338-1156782bdf7e@suse.cz>
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On 6 Aug 2021, at 12:32, Vlastimil Babka wrote:

> On 8/5/21 9:02 PM, Zi Yan wrote:
>> From: Zi Yan <ziy@nvidia.com>
>>
>> Hi all,
>>
>> This patchset add support for kernel boot time adjustable MAX_ORDER, s=
o that
>> user can change the largest size of pages obtained from buddy allocato=
r. It also
>> removes the restriction on MAX_ORDER based on SECTION_SIZE_BITS, so th=
at
>> buddy allocator can merge PFNs across memory sections when SPARSEMEM_V=
MEMMAP is
>> set. It is on top of v5.14-rc4-mmotm-2021-08-02-18-51.
>>
>> Motivation
>> =3D=3D=3D
>>
>> This enables kernel to allocate 1GB pages and is necessary for my ongo=
ing work
>> on adding support for 1GB PUD THP[1]. This is also the conclusion I ca=
me up with
>> after some discussion with David Hildenbrand on what methods should be=
 used for
>> allocating gigantic pages[2], since other approaches like using CMA al=
locator or
>> alloc_contig_pages() are regarded as suboptimal.
>
> I see references [1] [2] etc but no list of links at the end, did you
> forgot to include?
Ah, I missed that. Sorry.

Here are the links:

[1] https://lore.kernel.org/linux-mm/20200928175428.4110504-1-zi.yan@sent=
=2Ecom/
[2] https://lore.kernel.org/linux-mm/e132fdd9-65af-1cad-8a6e-71844ebfe6a2=
@redhat.com/
[3] https://lore.kernel.org/linux-mm/289DA3C0-9AE5-4992-A35A-C13FCE4D8544=
@nvidia.com/

BTW, [3] is the performance test I did to compare MAX_ORDER=3D11 and MAX_=
ORDER=3D20,
which showed no performance impact of increasing MAX_ORDER.

In addition, I would like to share more detail on my plan on supporting 1=
GB PUD THP.
This patchset is the first step, enabling kernel to allocate 1GB pages, s=
o that
user can get 1GB THPs from ZONE_NORMAL and ZONE_MOVABLE without using
alloc_contig_pages() or CMA allocator. The next step is to improve kernel=
 memory
fragmentation handling for pages up to MAX_ORDER, since currently pageblo=
ck size
is still limited by memory section size. As a result, I will explore solu=
tions
like having additional larger pageblocks (up to MAX_ORDER) to counter mem=
ory
fragmentation. I will discover what else needs to be solved as I graduall=
y improve
1GB PUD THP support.

=E2=80=94
Best Regards,
Yan, Zi

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