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

To: Michal Hocko <mhocko@xxxxxxxx>, Muchun Song <songmuchun@xxxxxxxxxxxxx>
Subject: Re: [PATCH v5 21/21] mm/hugetlb: Disable freeing vmemmap if struct page size is not power of two
From: David Hildenbrand <david@xxxxxxxxxx>
Date: Fri, 20 Nov 2020 10:15:30 +0100
Cc: 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
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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

Follow-Ups:
- Re: [PATCH v5 21/21] mm/hugetlb: Disable freeing vmemmap if struct page size is not power of two
  - From: Mike Rapoport

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