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Date: Mon, 23 Nov 2020 11:14:59 +0800 From: Muchun Song <songmuchun@...edance.com> To: Matthew Wilcox <willy@...radead.org> Cc: Michal Hocko <mhocko@...e.com>, Jonathan Corbet <corbet@....net>, Mike Kravetz <mike.kravetz@...cle.com>, Thomas Gleixner <tglx@...utronix.de>, mingo@...hat.com, bp@...en8.de, x86@...nel.org, hpa@...or.com, dave.hansen@...ux.intel.com, luto@...nel.org, Peter Zijlstra <peterz@...radead.org>, viro@...iv.linux.org.uk, Andrew Morton <akpm@...ux-foundation.org>, paulmck@...nel.org, mchehab+huawei@...nel.org, pawan.kumar.gupta@...ux.intel.com, Randy Dunlap <rdunlap@...radead.org>, oneukum@...e.com, anshuman.khandual@....com, jroedel@...e.de, Mina Almasry <almasrymina@...gle.com>, David Rientjes <rientjes@...gle.com>, Oscar Salvador <osalvador@...e.de>, "Song Bao Hua (Barry Song)" <song.bao.hua@...ilicon.com>, Xiongchun duan <duanxiongchun@...edance.com>, linux-doc@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>, Linux Memory Management List <linux-mm@...ck.org>, linux-fsdevel <linux-fsdevel@...r.kernel.org> Subject: Re: [External] Re: [PATCH v5 21/21] mm/hugetlb: Disable freeing vmemmap if struct page size is not power of two On Mon, Nov 23, 2020 at 3:00 AM Matthew Wilcox <willy@...radead.org> wrote: > > On Fri, Nov 20, 2020 at 09:25:52AM +0100, 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? > > Yes. On x86-64, if you don't enable MEMCG, it's 56 bytes. On SPARC64, > if you do enable MEMCG, it's 72 bytes. On 32-bit systems, it's > anything from 32-44 bytes, depending on MEMCG, WANT_PAGE_VIRTUAL and > LAST_CPUPID_NOT_IN_PAGE_FLAGS. > On x86-64, even if you do not enable MEMCG, it's also 64 bytes. Because CONFIG_HAVE_ALIGNED_STRUCT_PAGE is defined if we use SLUB. -- Yours, Muchun
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