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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Message-ID: <20201122133030.GG8537@kernel.org>
Date:   Sun, 22 Nov 2020 15:30:30 +0200
From:   Mike Rapoport <rppt@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     Michal Hocko <mhocko@...e.com>,
        Muchun Song <songmuchun@...edance.com>, 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 Fri, Nov 20, 2020 at 10:15:30AM +0100, David Hildenbrand wrote:
> 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.

Or multiples of 4 for 32-bit (28, 32, 36). 
 
> -- 
> Thanks,
> 
> David / dhildenb
> 
> 

-- 
Sincerely yours,
Mike.