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Date: Mon, 23 Nov 2020 08:48:04 +0100 From: Michal Hocko <mhocko@...e.com> To: Muchun Song <songmuchun@...edance.com> Cc: 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>, Matthew Wilcox <willy@...radead.org>, 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 13/21] mm/hugetlb: Use PG_slab to indicate split pmd On Fri 20-11-20 17:30:27, Muchun Song wrote: > On Fri, Nov 20, 2020 at 4:16 PM Michal Hocko <mhocko@...e.com> wrote: > > > > On Fri 20-11-20 14:43:17, Muchun Song wrote: > > > When we allocate hugetlb page from buddy, we may need split huge pmd > > > to pte. When we free the hugetlb page, we can merge pte to pmd. So > > > we need to distinguish whether the previous pmd has been split. The > > > page table is not allocated from slab. So we can reuse the PG_slab > > > to indicate that the pmd has been split. > > > > PageSlab is used outside of the slab allocator proper and that code > > might get confused by this AFAICS. > > I got your concerns. Maybe we can use PG_private instead of the > PG_slab. Reusing a page flag arbitrarily is not that easy. Hugetlb pages have a lot of spare room in struct page so I would rather use something else. -- Michal Hocko SUSE Labs
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