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Message-ID: <103fea0a-8a5e-a8ec-e956-a4341906218e@redhat.com>
Date:   Wed, 19 Apr 2023 13:10:27 +0200
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Subject: Re: [RFC PATCH 03/26] mm: make pageblock_order 2M per default
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To:     "Kirill A. Shutemov" <kirill@shutemov.name>,
        Johannes Weiner <hannes@cmpxchg.org>
Cc:     linux-mm@kvack.org, Kaiyang Zhao <kaiyang2@cs.cmu.edu>,
        Mel Gorman <mgorman@techsingularity.net>,
        Vlastimil Babka <vbabka@suse.cz>,
        David Rientjes <rientjes@google.com>,
        linux-kernel@vger.kernel.org, kernel-team@fb.com
References: <20230418191313.268131-1-hannes@cmpxchg.org>
 <20230418191313.268131-4-hannes@cmpxchg.org>
 <20230419000105.matz43p6ihrqmado@box.shutemov.name>
From:   David Hildenbrand <david@redhat.com>
Organization: Red Hat
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On 19.04.23 02:01, Kirill A. Shutemov wrote:
> On Tue, Apr 18, 2023 at 03:12:50PM -0400, Johannes Weiner wrote:
>> pageblock_order can be of various sizes, depending on configuration,
>> but the default is MAX_ORDER-1.
> 
> Note that MAX_ORDER got redefined in -mm tree recently.
> 
>> Given 4k pages, that comes out to
>> 4M. This is a large chunk for the allocator/reclaim/compaction to try
>> to keep grouped per migratetype. It's also unnecessary as the majority
>> of higher order allocations - THP and slab - are smaller than that.
> 
> This seems way to x86-specific. Other arches have larger THP sizes. I
> believe 16M is common.
> 

arm64 with 64k pages has ... 512 MiB IIRC :/ It's the weird one.

> Maybe define it as min(MAX_ORDER, PMD_ORDER)?

Sounds good to me.

-- 
Thanks,

David / dhildenb