linux-kernel - Re: [PATCH v5 21/21] mm/hugetlb: Disable freeing vmemmap if struct page size is not power of two

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Date:   Fri, 20 Nov 2020 10:15:30 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Michal Hocko <mhocko@...e.com>,
        Muchun Song <songmuchun@...edance.com>
Cc:     corbet@....net, mike.kravetz@...cle.com, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, x86@...nel.org, hpa@...or.com,
        dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org,
        viro@...iv.linux.org.uk, akpm@...ux-foundation.org,
        paulmck@...nel.org, mchehab+huawei@...nel.org,
        pawan.kumar.gupta@...ux.intel.com, rdunlap@...radead.org,
        oneukum@...e.com, anshuman.khandual@....com, jroedel@...e.de,
        almasrymina@...gle.com, rientjes@...gle.com, willy@...radead.org,
        osalvador@...e.de, song.bao.hua@...ilicon.com,
        duanxiongchun@...edance.com, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v5 21/21] mm/hugetlb: Disable freeing vmemmap if struct
 page size is not power of two

On 20.11.20 09:25, Michal Hocko wrote:
> On Fri 20-11-20 14:43:25, Muchun Song wrote:
>> We only can free the unused vmemmap to the buddy system when the
>> size of struct page is a power of two.
> 
> Can we actually have !power_of_2 struct pages?

AFAIK multiples of 8 bytes (56, 64, 72) are possible.


-- 
Thanks,

David / dhildenb