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AJvYcCWYCYemmgSeNukMaJDIPqCU2Q4+tApknEjJlVb4mbarDASPdMdBVcB69bF0KNBb4wnOBtxiawf+mQ==@kvack.org X-Gm-Message-State: AOJu0YzQSF0ypWjhyRwpR/RYpSegKxobMcVadm4LqgkNyDCaTqDJYDYp Vpr0DRsMpTG5/GGxbJWkOR/fwuOgGS5j5lAMWT5j0RD/XFwzwwGHe+Q45VRSZhE= X-Google-Smtp-Source: AGHT+IGSnKMa6ka5pGSYL/mBuk3Wz5Gb7lASbW1uGNq3aUIUquaCO5kb+R042BsY8/svwsYky7FbCA== X-Received: by 2002:a05:6a20:7491:b0:1d9:dc8:b80d with SMTP id adf61e73a8af0-1dc234fd966mr23052302637.20.1731369267319; Mon, 11 Nov 2024 15:54:27 -0800 (PST) Received: from [192.168.1.150] ([198.8.77.157]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-724079aa8fasm9775141b3a.97.2024.11.11.15.54.26 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 11 Nov 2024 15:54:26 -0800 (PST) Message-ID: Date: Mon, 11 Nov 2024 16:54:25 -0700 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCHSET v4] Uncached buffered IO From: Jens Axboe To: Stefan Metzmacher , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Cc: hannes@cmpxchg.org, clm@meta.com, linux-kernel@vger.kernel.org References: <20241108174505.1214230-1-axboe@kernel.dk> <63af3bba-c824-4b2c-a670-6329eeb232aa@samba.org> <00c51f80-7033-44a0-b007-ca36842e35a5@kernel.dk> <76edefe6-fb20-4169-8cbe-d8b864b04c7a@kernel.dk> Content-Language: en-US In-Reply-To: <76edefe6-fb20-4169-8cbe-d8b864b04c7a@kernel.dk> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 8EFE11C001A X-Stat-Signature: 7a64bp6t9rdxb7pntdmide388xutu51q X-Rspam-User: X-HE-Tag: 1731369250-995337 X-HE-Meta: U2FsdGVkX1/VaRkABZJSmRTuNDjrIBunbkWVLTuy1+XtXjYby9WYq35qnRHG0h/86tQNW3gNV9LEMbBwSBGfz8ormicL9xbUtCbGey5uC0kJPhhL4SBpCuz0eX3fkXSES/C5wma/tXM5ZnfUvmeeu8lg9sXDc+bpceufPRCvziw3ktMVsWOkIr8DP2aGsmq200csTlSGjdAnVqbOuUFSualsv2q+VKA+sj8HNoI4TQ1kaJSn9q8NPW5ufKRbX8qMXL5DtOTHbz3e1aISKuxr6gm2lHsDTYiO8wYopNeD3xRW+R6q+Qwud+w1+82mQhfBHxh3zY4AKY2h7E5lXS/p2jeo8cUUoLfMJUZFdQdQQoP6oLBtFsOQ35K93LdYhBfrtNivdU2eyCRjzDbGYdZk54C93/KSYZLxO4B2ozq1rHA+FZ6DGzaeDVxDnu7M9ZFh1/aL0E65lteK8hLkDkprzmHRAV0LNMvPibmahWPaGENtS9q028QeMUF8J+uHjFNzdtwmY9mQa/8zVwzauZ9IM6B/uMnyTECgPkv3NYUulxBFmT/UZFRoo750MU3UudHX2AUgu9/+YfvZvWBGGJQ5jzIdW6iMQY1A5T/rYIJLNZScjcm/25yZtSA1waQsTSsKEdIFWQSUE7FM3zDQ8pTdgRtAKYGEZyYfDHSZBBFYKf4GfPW2zJCSBpkXiL+ISeWdfUw/bs5xmgpvwn9XZSYhR6GRWWV98SUAcFytlXRxu5Rs+/VhFb1kVlOz3MxRAGhx77NuMJwK1fjRVrrfOGmACbOJl1myAFAxUC5zmh9tyHJKBeBbVaxVdNphjifQ4IgRsgp8ml6ne7+ODUSB2/ofWkPGplxys8OgDvp3sRkdAuQYFhXZ5Kz4BU8buLNh6Pb9n+H+T8QFXL0FP2ZyxvOQusSLo524SiEIm0FWenhWwnnW2DYVrCd69xo2/hzFFFKtafSmx+j3jOXu18mPLxm enbhKHk5 EQo/V5QbWy1OLcPoDuvxEQNse/2j+ylhK+M2vB4ll9sqDayJADyJFGNgLDulCzij0f5EVNh3AXWUxPE0v3nzHuCgUjyvwVHOYfox0JP11WUWbhZLt/l9JKc3JopqEElhQCX4TFcadjQ2m+BKBuuJt9uvjN66tYe95WJ2LQzlxgAC92//XmGyqtA42O8nPNWmZ0sqk6egEE0IORD5V6tlnY+r9Dk+jGo462K2bkqd4HllMjkcN33nbzTkyV62xBQhg9lC0C/qIX3G/NQzkSe839X4pOYFlwIjNSFfneSrJ5Icx8zpbktzVLEfCkI+czG0zl2wjgpYlrWprjlmElviq+Q2sfMcAM/+TEVBx X-Bogosity: Ham, tests=bogofilter, spamicity=0.000050, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 11/11/24 8:05 AM, Jens Axboe wrote: > On 11/11/24 7:08 AM, Jens Axboe wrote: >> On 11/11/24 5:55 AM, Stefan Metzmacher wrote: >>> Hi Jens, >>> >>> I'm wondering about the impact on memory mapped files. >>> >>> Let's say one (or more) process(es) called mmap on a file in order to >>> use the content of the file as persistent shared memory. >>> As far as I understand pages from the page cache are used for this. >>> >>> Now another process uses RWF_UNCACHED for a read of the same file. >>> What happens if the pages are removed from the page cache? >>> Or is the removal deferred based on some refcount? >> >> For mmap, if a given page isn't in page cache, it'll get faulted in. >> Should be fine to have mmap and uncached IO co-exist. If an uncached >> read IO instantiates a page, it'll get reaped when the data has been >> copied. If an uncached IO hits an already existing page (eg mmap faulted >> it in), then it won't get touched. Same thing happens with mixing >> buffered and uncached IO. The latter will only reap parts it >> instantiated to satisfy the operation. That doesn't matter in terms of >> data integrity, only in terms of the policy of uncached leaving things >> alone it didn't create to satisfy the operation. >> >> This is really no different than say using mmap and evicting pages, they >> will just get faulted in if needed. > > Turns out that was nonsense, as per Kiril's comments on the other thread. > For pages that are actually mapped, we'll have to skip the invalidation > as it's not safe to do so. ...and now v3 (just posted) actually does work like I described, it'll co-exist with mmap. -- Jens Axboe