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[2001:b011:20e0:15d4:84b3:8c62:a0b8:199e]) by smtp.gmail.com with ESMTPSA id x2-20020a170902ec8200b0015e8d4eb234sm590603plg.126.2022.05.20.22.10.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 20 May 2022 22:10:22 -0700 (PDT) Date: Sat, 21 May 2022 13:10:14 +0800 From: Chih-En Lin To: Matthew Wilcox Cc: Andrew Morton , linux-mm@kvack.org, Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Christian Brauner , Vlastimil Babka , William Kucharski , John Hubbard , Yunsheng Lin , Arnd Bergmann , Suren Baghdasaryan , Colin Cross , Feng Tang , "Eric W. Biederman" , Mike Rapoport , Geert Uytterhoeven , Anshuman Khandual , "Aneesh Kumar K.V" , Daniel Axtens , Jonathan Marek , Christophe Leroy , Pasha Tatashin , Peter Xu , Andrea Arcangeli , Thomas Gleixner , Andy Lutomirski , Sebastian Andrzej Siewior , Fenghua Yu , David Hildenbrand , linux-kernel@vger.kernel.org, Kaiyang Zhao , Huichun Feng , Jim Huang Subject: Re: [RFC PATCH 5/6] mm, pgtable: Add the reference counter for COW PTE Message-ID: <20220521051014.GE1508515@strix-laptop> References: <20220519183127.3909598-1-shiyn.lin@gmail.com> <20220519183127.3909598-6-shiyn.lin@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 170D51400DA X-Stat-Signature: 7r95uenrj3i88kxa8yjddq4bw4cuuw7n Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=cqAJFUxn; spf=pass (imf26.hostedemail.com: domain of shiyn.lin@gmail.com designates 209.85.210.172 as permitted sender) smtp.mailfrom=shiyn.lin@gmail.com; dmarc=pass (policy=none) header.from=gmail.com X-Rspam-User: X-HE-Tag: 1653109819-222115 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sat, May 21, 2022 at 05:08:09AM +0100, Matthew Wilcox wrote: > On Fri, May 20, 2022 at 02:31:26AM +0800, Chih-En Lin wrote: > > +++ b/include/linux/mm_types.h > > @@ -221,6 +221,7 @@ struct page { > > #ifdef LAST_CPUPID_NOT_IN_PAGE_FLAGS > > int _last_cpupid; > > #endif > > + atomic_t cow_pgtable_refcount; /* COW page table */ > > pmd_t *cow_pte_owner; /* cow pte: pmd */ > > } _struct_page_alignment; > > Oh. You need another 4 bytes. Hmm. > > Can you share _refcount? > > Using _pt_pad_2 should be possible, but some care will be needed to make > sure it's (a) in a union with an unsigned long to keep the alignment > as expected, and (b) is definitely zero before the page is freed (or > the page allocator will squawk at you). _refcount may be better. I will try this at first, and if any other thing let _refcount cannot be used, I will consider _pt_pad_2. Thanks!