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[2001:b011:20e0:15d4:84b3:8c62:a0b8:199e]) by smtp.gmail.com with ESMTPSA id t2-20020a170902e84200b0015e8d4eb273sm495371plg.189.2022.05.20.21.15.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 20 May 2022 21:15:16 -0700 (PDT) Date: Sat, 21 May 2022 12:15:08 +0800 From: Chih-En Lin To: Christophe Leroy 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 , "Matthew Wilcox (Oracle)" , 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 , 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 4/6] mm: Add COW PTE fallback function Message-ID: <20220521041508.GA1508515@strix-laptop> References: <20220519183127.3909598-1-shiyn.lin@gmail.com> <20220519183127.3909598-5-shiyn.lin@gmail.com> <68c8a99e-52b5-9bbf-4847-3337165d99a8@csgroup.eu> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <68c8a99e-52b5-9bbf-4847-3337165d99a8@csgroup.eu> X-Rspam-User: X-Rspamd-Queue-Id: B1EF0C0013 X-Stat-Signature: hz793imgqokcoc4g64soqd3hajyg9yzt Authentication-Results: imf22.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=f9o6lYyK; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (imf22.hostedemail.com: domain of shiyn.lin@gmail.com designates 209.85.210.179 as permitted sender) smtp.mailfrom=shiyn.lin@gmail.com X-Rspamd-Server: rspam04 X-HE-Tag: 1653106515-611779 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 Fri, May 20, 2022 at 02:21:54PM +0000, Christophe Leroy wrote: > > +/* COW PTE fallback to normal PTE: > > + * - two state here > > + * - After break child : [parent, rss=1, ref=1, write=NO , owner=parent] > > + * to [parent, rss=1, ref=1, write=YES, owner=NULL ] > > + * - After break parent: [child , rss=0, ref=1, write=NO , owner=NULL ] > > + * to [child , rss=1, ref=1, write=YES, owner=NULL ] > > + */ > > +void cow_pte_fallback(struct vm_area_struct *vma, pmd_t *pmd, > > + unsigned long addr) > > There should be a prototype in a header somewhere for a non static function. > > You are encouraged to run 'make mm/memory.o C=2' to check sparse reports. > I will do all the above checking before sending the next version. > > +{ > > + struct mm_struct *mm = vma->vm_mm; > > + unsigned long start, end; > > + pmd_t new; > > + > > + BUG_ON(pmd_write(*pmd)); > > You seem to add a lot of BUG_ONs(). Are they really necessary ? See > https://docs.kernel.org/process/deprecated.html?highlight=bug_on#bug-and-bug-on > > You may also use VM_BUG_ON(). > Sure. I added BUG_ON() when doing the debug. I will consider again which one is necessary. And change to use VM_BUG_ON(). Thanks.