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[184.145.104.227]) by smtp.gmail.com with ESMTPSA id g135sm3084697qke.8.2021.04.22.14.18.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 22 Apr 2021 14:18:49 -0700 (PDT) Date: Thu, 22 Apr 2021 17:18:47 -0400 From: Peter Xu To: Axel Rasmussen Cc: Alexander Viro , Andrea Arcangeli , Andrew Morton , Hugh Dickins , Jerome Glisse , Joe Perches , Lokesh Gidra , Mike Kravetz , Mike Rapoport , Shaohua Li , Shuah Khan , Stephen Rothwell , Wang Qing , linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, LKML , linux-kselftest@vger.kernel.org, Linux MM , Brian Geffon , "Dr . David Alan Gilbert" , Mina Almasry , Oliver Upton Subject: Re: [PATCH v4 03/10] userfaultfd/shmem: support UFFDIO_CONTINUE for shmem Message-ID: <20210422211847.GF6404@xz-x1> References: <20210420220804.486803-1-axelrasmussen@google.com> <20210420220804.486803-4-axelrasmussen@google.com> 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-Rspamd-Queue-Id: 4A99DE000126 X-Stat-Signature: m4eyqymb8nxw5h4zkp9xabhskcjjfjsx X-Rspamd-Server: rspam02 Received-SPF: none (redhat.com>: No applicable sender policy available) receiver=imf30; identity=mailfrom; envelope-from=""; helo=us-smtp-delivery-124.mimecast.com; client-ip=216.205.24.124 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1619126318-675025 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000002, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Axel, On Thu, Apr 22, 2021 at 01:22:02PM -0700, Axel Rasmussen wrote: > > + if (page_in_cache) > > + page_add_file_rmap(page, false); > > + else > > + page_add_new_anon_rmap(page, dst_vma, dst_addr, false); > > + > > + /* > > + * Must happen after rmap, as mm_counter() checks mapping (via > > + * PageAnon()), which is set by __page_set_anon_rmap(). > > + */ > > + inc_mm_counter(dst_mm, mm_counter(page)); > > Actually, I've noticed that this is still slightly incorrect. > > As Hugh pointed out, this works for the anon case, because > page_add_new_anon_rmap() sets page->mapping. > > But for the page_in_cache case, it doesn't work: unlike its anon > counterpart, page_add_file_rmap() *does not* set page->mapping. If it's already in the page cache, shouldn't it be set already in e.g. one previous call to shmem_add_to_page_cache()? Thanks, -- Peter Xu