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[2003:cb:c703:d00:ca74:d9ea:11e0:dfb]) by smtp.gmail.com with ESMTPSA id s11-20020adff80b000000b002d6f285c0a2sm8066858wrp.42.2023.03.22.10.02.35 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 22 Mar 2023 10:02:36 -0700 (PDT) Message-ID: <3e2d1f69-5cd8-8824-0a2e-a1c2c9029f66@redhat.com> Date: Wed, 22 Mar 2023 18:02:34 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.9.0 Subject: Re: [PATCH v6 4/4] mm: vmalloc: convert vread() to vread_iter() To: Lorenzo Stoakes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Andrew Morton Cc: Baoquan He , Uladzislau Rezki , Matthew Wilcox , Liu Shixin , Jiri Olsa , Jens Axboe , Alexander Viro References: <4f1b394f96a4d1368d9a5c3784ebee631fb8d101.1679496827.git.lstoakes@gmail.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <4f1b394f96a4d1368d9a5c3784ebee631fb8d101.1679496827.git.lstoakes@gmail.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: 3027D8002F X-Rspamd-Server: rspam01 X-Stat-Signature: c59ze5sthc3qsjpmqu9m5x36zp4eg768 X-HE-Tag: 1679504566-262783 X-HE-Meta: U2FsdGVkX1/UPXRFZdxudo5CUiSla3cSAbQRQ/8RbIc6jhytHVtxGu+dr3rYq4RBFyENdZN61powqhhiWKlmVn/VRvLFpJQ41WQXJoRAYMtRhchz+D+4CXpQXWwuO+OHpFDzwxqGzXIOtONxu5XcQdZK/esphHKinETIbxDT0VLzQJl4Mg8kr+YMYs0eYtBeJ3CoX+m5hkfIoqgdq25ekQ4UkuE2BfJMJvXKIOkuhNgfVYzN4qQV+KvITTXwLyrKO1OreZT7ETKRf4uBKL2F5TyAk/Zknew+i8KyxiqlUqNne39lkM6RnscY/iYJsE+GJ+Re+HI+U+wHFfx6nmTPSOQudSyjHNLYqtF5H2DuiMDh1POLAHAmlxIX2LY8rDr3GhJ/58tuaT8h5ndnLI0eSoQTX+SzvguK1U2A0tFtlOa2FxuCDGFhNygJM5nuc5WwWEbx2lu/1k80a5ijS/oo+Lw/XLOwNq9jfa6uZoC9P4EHkGIrJ16SKd9S07n/3jsXRbL3MOEZgjLjJel+rxjzdb/31iM5keoOZIcrnuiFJz0nwCtNEDm02I02RLwySW9zO1Rionq7AcsMcl/DT1WO3kR1iQ2Jl0NLiNUH8zXMdcioZssbsRaTtdpDQejPgv2vHSC8LDiLsPCXtDH/tCwnytmNv5HWUDq2FJzJvMrk36wUdCyBe+E5SMJKb/cJN43jIEASbozveoCO36eS4pRwwV6cRH6PbzIJWe1HklCviB9HIOJ/CWkOlvuNzi24PrrbQia9EDjlMTcfcKfyOdLMsRnb9aDEbfEJ1ChTcjtf55jIpqVVUzJfFfV+q9zrl4MDxpN3E4nvojwYjD9lRDGmVkgybk2AOf3SPdpYn1sUQKTvABrtDTQo1PIrzrsi2kXCvYSKrkHMgr4lwz8sxrx2Rs6qOd5dH7nxaToisyWcd6624c8U0wGaRtJennC8JxI986OcqfmsuhIV8qPE+cf jy5sOfoI iDyfS0y0J31LHeQoUoJVHy+TDNbkD+0k1OsHguZkaVrfagCu/XbPf7IiwwQT25L5M4yQgaFfEQPg96x/5db4SQk2t+iW7s8yUDIz36WksAeU005OnzPfP7isKgXR2v12MFEXgHmR3gw8VdO9DElgsgGso648/sNrGw0JNChsN3hvtilXbjPaUo95loeAA0CaUTrk3x81FEkTpUHhHmclyRJnLy5l9gpWc7AvI+2YcmkMGwdM0bY7il1Zf++aRlSTdaVcg1xNbfJpadfpAZjeOlj360069vns9E7ZM0FkQZ2zUUEyEIEtqYAEsXtSrQjMJeZkrodrPAQdht8LGQV09yhwJ5DADi2odgqrCu3rQR947iK3VarUFgK3vgGYpqhjskJ32od77oqgflHBoI3dVZs7t5FdamMCag6/CarrPyCrECpacpFE4KBlEa3M5YJdgvSqw 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 22.03.23 15:55, Lorenzo Stoakes wrote: > Having previously laid the foundation for converting vread() to an iterator > function, pull the trigger and do so. > > This patch attempts to provide minimal refactoring and to reflect the > existing logic as best we can, for example we continue to zero portions of > memory not read, as before. > > Overall, there should be no functional difference other than a performance > improvement in /proc/kcore access to vmalloc regions. > > Now we have eliminated the need for a bounce buffer in read_kcore_iter(), > we dispense with it, and try to write to user memory optimistically but > with faults disabled via copy_page_to_iter_nofault(). We already have > preemption disabled by holding a spin lock. > > If this fails, we fault in and retry a single time. This is a conservative > approach intended to avoid spinning on vread_iter() if we repeatedly > encouter issues reading from it. I have to ask again: Can you comment why that is ok? You might end up signaling -EFAULT to user space simply because swapping/page migration/whatever triggered at the wrong time. That could break existing user space or which important part am I missing? -- Thanks, David / dhildenb