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

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To: David Hildenbrand <david@xxxxxxxxxx>
Subject: Re: [PATCH v5 21/21] mm/hugetlb: Disable freeing vmemmap if struct page size is not power of two
From: Mike Rapoport <rppt@xxxxxxxxxx>
Date: Sun, 22 Nov 2020 15:30:30 +0200
Cc: Michal Hocko <mhocko@xxxxxxxx>, Muchun Song <songmuchun@xxxxxxxxxxxxx>, corbet@xxxxxxx, mike.kravetz@xxxxxxxxxx, tglx@xxxxxxxxxxxxx, mingo@xxxxxxxxxx, bp@xxxxxxxxx, x86@xxxxxxxxxx, hpa@xxxxxxxxx, dave.hansen@xxxxxxxxxxxxxxx, luto@xxxxxxxxxx, peterz@xxxxxxxxxxxxx, viro@xxxxxxxxxxxxxxxxxx, akpm@xxxxxxxxxxxxxxxxxxxx, paulmck@xxxxxxxxxx, mchehab+huawei@xxxxxxxxxx, pawan.kumar.gupta@xxxxxxxxxxxxxxx, rdunlap@xxxxxxxxxxxxx, oneukum@xxxxxxxx, anshuman.khandual@xxxxxxx, jroedel@xxxxxxx, almasrymina@xxxxxxxxxx, rientjes@xxxxxxxxxx, willy@xxxxxxxxxxxxx, osalvador@xxxxxxx, song.bao.hua@xxxxxxxxxxxxx, duanxiongchun@xxxxxxxxxxxxx, linux-doc@xxxxxxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, linux-mm@xxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx
In-reply-to: <9b26c749-3bb6-4b16-d1fc-da7ec5d1e8a5@redhat.com>
References: <20201120064325.34492-1-songmuchun@bytedance.com> <20201120064325.34492-22-songmuchun@bytedance.com> <20201120082552.GI3200@dhcp22.suse.cz> <9b26c749-3bb6-4b16-d1fc-da7ec5d1e8a5@redhat.com>

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.

References:
- [PATCH v5 00/21] Free some vmemmap pages of hugetlb page
  - From: Muchun Song
- [PATCH v5 21/21] mm/hugetlb: Disable freeing vmemmap if struct page size is not power of two
  - From: Muchun Song
- Re: [PATCH v5 21/21] mm/hugetlb: Disable freeing vmemmap if struct page size is not power of two
  - From: Michal Hocko
- Re: [PATCH v5 21/21] mm/hugetlb: Disable freeing vmemmap if struct page size is not power of two
  - From: David Hildenbrand

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