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[70.53.122.15]) by smtp.gmail.com with ESMTPSA id d9sm2487108qtg.51.2020.09.24.08.47.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 24 Sep 2020 08:47:52 -0700 (PDT) Date: Thu, 24 Sep 2020 11:47:50 -0400 From: Peter Xu To: Yang Shi Cc: Jason Gunthorpe , Linux MM , Linux Kernel Mailing List , Linus Torvalds , Michal Hocko , Kirill Shutemov , Jann Horn , Oleg Nesterov , Kirill Tkhai , Hugh Dickins , Leon Romanovsky , Jan Kara , John Hubbard , Christoph Hellwig , Andrew Morton , Andrea Arcangeli Subject: Re: [PATCH 5/5] mm/thp: Split huge pmds/puds if they're pinned when fork() Message-ID: <20200924154750.GG79898@xz-x1> References: <20200921211744.24758-1-peterx@redhat.com> <20200921212031.25233-1-peterx@redhat.com> <20200922120505.GH8409@ziepe.ca> <20200923152409.GC59978@xz-x1> MIME-Version: 1.0 In-Reply-To: Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=peterx@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline 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 Wed, Sep 23, 2020 at 09:07:49AM -0700, Yang Shi wrote: > For tmpfs map, the pmd split just clears the pmd entry without > reinstalling ptes (oppositely anonymous map would reinstall ptes). It > looks this patch intends to copy at pte level by splitting pmd. But > I'm afraid this may not work for tmpfs mappings. IIUC that's exactly what we want. We only want to make sure the pinned tmpfs shared pages will be kept there in the parent. It's not a must to copy the pages to the child, as long as they can be faulted in later correctly. -- Peter Xu