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[174.91.135.175]) by smtp.gmail.com with ESMTPSA id l4sm984629qkd.105.2021.04.09.09.50.25 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 09 Apr 2021 09:50:26 -0700 (PDT) Date: Fri, 9 Apr 2021 12:50:24 -0400 From: Peter Xu To: Axel Rasmussen Cc: Alexander Viro , Andrea Arcangeli , Andrew Morton , Daniel Colascione , 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, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, Brian Geffon , "Dr . David Alan Gilbert" , Mina Almasry , Oliver Upton Subject: Re: [PATCH 3/9] userfaultfd/shmem: support minor fault registration for shmem Message-ID: <20210409165024.GF792100@xz-x1> References: <20210408234327.624367-1-axelrasmussen@google.com> <20210408234327.624367-4-axelrasmussen@google.com> MIME-Version: 1.0 In-Reply-To: <20210408234327.624367-4-axelrasmussen@google.com> 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-Server: rspam03 X-Rspamd-Queue-Id: D04A3E000114 X-Stat-Signature: hz3kwwmddxy9bik1istp3surfda3ccob Received-SPF: none (redhat.com>: No applicable sender policy available) receiver=imf21; 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: 1617987029-789037 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 Thu, Apr 08, 2021 at 04:43:21PM -0700, Axel Rasmussen wrote: [...] > @@ -1820,16 +1821,27 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index, > > page = pagecache_get_page(mapping, index, > FGP_ENTRY | FGP_HEAD | FGP_LOCK, 0); > - if (xa_is_value(page)) { > + swapped = xa_is_value(page); > + if (swapped) { > error = shmem_swapin_page(inode, index, &page, > sgp, gfp, vma, fault_type); > if (error == -EEXIST) > goto repeat; > - > *pagep = page; > - return error; > + if (error) > + return error; > } > > + if (page && vma && userfaultfd_minor(vma)) { > + unlock_page(page); > + put_page(page); > + *fault_type = handle_userfault(vmf, VM_UFFD_MINOR); > + return 0; > + } If we need to consider swapping for UFFDIO_CONTINUE later (as Hugh pointed out previously, which looks the right thing to do), it's indeed a bit awkward to swapin here. Maybe move this chunk to right after pagecache_get_page() returns? Then no need to touch the rest. > + > + if (swapped) > + return 0; > + > if (page) > hindex = page->index; > if (page && sgp == SGP_WRITE) > -- > 2.31.1.295.g9ea45b61b8-goog > -- Peter Xu