linux-kernel - Re: [RFC 2/3] arm64/hugetlb: Enable HUGETLB_PAGE_SIZE

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Message-ID: <ca668991-4ea1-6476-8be0-8c0db96a682e@arm.com>
Date:   Fri, 5 Feb 2021 14:00:11 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     David Hildenbrand <david@...hat.com>, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org, catalin.marinas@....com,
        akpm@...ux-foundation.org
Cc:     Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Christoph Hellwig <hch@....de>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC 2/3] arm64/hugetlb: Enable HUGETLB_PAGE_SIZE_VARIABLE



On 2/5/21 1:50 PM, David Hildenbrand wrote:
> On 04.02.21 08:01, Anshuman Khandual wrote:
>> MAX_ORDER which invariably depends on FORCE_MAX_ZONEORDER can be a variable
>> for a given page size, depending on whether TRANSPARENT_HUGEPAGE is enabled
>> or not. In certain page size and THP combinations HUGETLB_PAGE_ORDER can be
>> greater than MAX_ORDER, making it unusable as pageblock_order.
> 
> Just so I understand correctly, this does not imply that we have THP that exceed the pageblock size / MAX_ORDER size, correct?

Correct. MAX_ORDER gets incremented when THP is enabled.

config FORCE_MAX_ZONEORDER
        int
        default "14" if (ARM64_64K_PAGES && TRANSPARENT_HUGEPAGE)
        default "12" if (ARM64_16K_PAGES && TRANSPARENT_HUGEPAGE)
        default "11"