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Petersen" , "axboe@kernel.dk" , josef@toxicpanda.com, Christoph Hellwig From: Kanchan Joshi In-Reply-To: Content-Transfer-Encoding: 7bit X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFtrIJsWRmVeSWpSXmKPExsWy7bCmpm7zpBupBv8WWlusvtvPZrFy9VEm iz8PDS0mHbrGaLH3lrbFnr0nWSzmL3vKbrHv9V5mi+XH/zE5cHpcPlvqsWlVJ5vH5iX1HpNv LGf02H2zgc3j49NbLB4TNm9k9fi8SS6AIyrbJiM1MSW1SCE1Lzk/JTMv3VbJOzjeOd7UzMBQ 19DSwlxJIS8xN9VWycUnQNctMwfoNiWFssScUqBQQGJxsZK+nU1RfmlJqkJGfnGJrVJqQUpO gUmBXnFibnFpXrpeXmqJlaGBgZEpUGFCdsaT7a0sBW1CFce2z2NpYNzE18XIySEhYCKxafZe ti5GLg4hgd2MEuv7prNCOJ8YJQ7u3QqV+QaUOX+EDaZl3/I+ZojEXkaJQweaoKreMkos7XzN DFLFK2An8bbxMzuIzSKgKrFg5UKouKDEyZlPWEBsUYEkiV9X5zCC2MICwRILb20EizMLiEvc ejKfCcQWEVCWuDt/JthNzAJvmSSu3PgK5HBwsAloSlyYXApSwymgJdF17i07RK+8xPa3c8Cu kxBYyyHRc2MyE8TZLhKXD62HsoUlXh3fwg5hS0m87G+DspMlLs08B1VTIvF4z0Eo216i9VQ/ M8heZqC963fpQ+zik+j9/YQJJCwhwCvR0SYEUa0ocW/SU1YIW1zi4YwlULaHxI/LJ6BhtYlR Yv/SbvYJjAqzkIJlFpL3ZyF5ZxbC5gWMLKsYJVMLinPTU4tNCwzzUsvhMZ6cn7uJEZx2tTx3 MN598EHvECMTB+MhRgkOZiUR3kvZN1KFeFMSK6tSi/Lji0pzUosPMZoC42cis5Rocj4w8eeV xBuaWBqYmJmZmVgamxkqifO+bp2bIiSQnliSmp2aWpBaBNPHxMEp1cCkrBXpe3674+RX7cce GL2v3O6y0MN6St71Dw8uHNeckLxP11uhxSNBpqbf5ayt/9H1AfLbEjTke5dervA55fMv9l1m 5ZbLjzyP+Ry3Z48qvCWhkXJpsTTrC54fn7k2zlRgXasU7svDWx342OrRv8yld55O1dx7tPpz WX1sWOn1oO+9Vq3L3huxfp+6jnlzkPibnhd+/6zcpIoOXkxcfjN1T8aEi1leD7/us7/3ckLz Xi6DhOS9y1j2VLCnWfy+yCe5fOmmwGOKk1epP6ifv5o3/+fUBycWh1o1fjv7bf+doHOhHRML pf3yFYw3vVjedDW2a+PH+4ttvs167/LDyPqMI3de1feH74V+vNqy4GfwdiWW4oxEQy3mouJE AO7TGFJEBAAA X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFuplkeLIzCtJLcpLzFFi42LZdlhJTrd50o1Ug+0v2C1W3+1ns1i5+iiT xZ+HhhaTDl1jtNh7S9tiz96TLBbzlz1lt9j3ei+zxfLj/5gcOD0uny312LSqk81j85J6j8k3 ljN67L7ZwObx8ektFo8JmzeyenzeJBfAEcVlk5Kak1mWWqRvl8CV8WR7K0tBm1DFse3zWBoY N/F1MXJySAiYSOxb3sfcxcjFISSwm1Fi7qT/7BAJcYnmaz+gbGGJlf+es0MUvWaU2Pj9NQtI glfATuJt42ewIhYBVYkFKxcyQ8QFJU7OfAJWIyqQJLHnfiMTiC0sECyx8NZGsDgz0IJbT+aD xUUElCXuzp/JCrKAWeA9k8T7D8+hTtrEKHFh3WfGLkYODjYBTYkLk0tBGjgFtCS6zr1lhxhk JtG1tYsRwpaX2P52DvMERqFZSO6YhWTfLCQts5C0LGBkWcUomVpQnJuem2xYYJiXWq5XnJhb XJqXrpecn7uJERxjWho7GO/N/6d3iJGJg/EQowQHs5II76XsG6lCvCmJlVWpRfnxRaU5qcWH GKU5WJTEeQ1nzE4REkhPLEnNTk0tSC2CyTJxcEo1MFkZzeRbE6E+V/GM9p/Qr1EN3js27tL3 W8DpdM/yrMO9Gaq6mvNddnOsv7Xpg4zXfXPXXQ6/+Rd7xNiu9bx9Ijp2L3/0GsvmoJBvt/kt wr+xSvzbY+szlWX2c0nlcwWtOn2Hbm18cO7wrh287Odmb5oos3dB3aW3F2QX2xbEnZi7cG3z LPUfR4S2feRRvrHEP9IkZ6OxbURF8W2nWTv1Uv7c+Js7oTxKJPbzYsG6kLNcfZud5manpv32 n5L24rPSC85T3loOutqPLrIuSz0X+Xify9VtP4IEeHdLxv9107mefW7iHeao51y7Fjc9Pik/ ozGgflHUpuaVdyYzbXy88Cony+8LjzvumSiuqzNxW7VRiaU4I9FQi7moOBEA5Y+AqSADAAA= X-CMS-MailID: 20240223124139epcas5p195356ca928b72fa08d679be1c926de4e X-Msg-Generator: CA Content-Type: text/plain; charset="utf-8" CMS-TYPE: 105P DLP-Filter: Pass X-CFilter-Loop: Reflected X-CMS-RootMailID: 20240222193304epcas5p318426c5267ee520e6b5710164c533b7d References: On 2/23/2024 1:38 AM, Keith Busch wrote: > On Fri, Feb 23, 2024 at 01:03:01AM +0530, Kanchan Joshi wrote: >> With respect to the current state of Meta/Block-integrity, there are >> some missing pieces. >> I can improve some of it. But not sure if I am up to speed on the >> history behind the status quo. >> >> Hence, this proposal to discuss the pieces. >> >> Maybe people would like to discuss other points too, but I have the >> following: >> >> - Generic user interface that user-space can use to exchange meta. A >> new io_uring opcode IORING_OP_READ/WRITE_META - seems feasible for >> direct IO. Buffered IO seems non-trivial as a relatively smaller meta >> needs to be written into/read from the page cache. The related >> metadata must also be written during the writeback (of data). >> >> >> - Is there interest in filesystem leveraging the integrity capabilities >> that almost every enterprise SSD has. >> Filesystems lacking checksumming abilities can still ask the SSD to do >> it and be more robust. >> And for BTRFS - there may be value in offloading the checksum to SSD. >> Either to save the host CPU or to get more usable space (by not >> writing the checksum tree). The mount option 'nodatasum' can turn off >> the data checksumming, but more needs to be done to make the offload >> work. > > As I understand it, btrfs's checksums are on a variable extent size, but > offloading it to the SSD would do it per block, so it's forcing a new > on-disk format. It would be cool to use it, though: you could atomically > update data and checksums without stable pages. > Yes, variable extents but it computes the checksum for each FS block size (4k-64K, practically 4K) within each extent. On-disk format change will not be needed, because in this approach FS (and block-integrity) does not really deal with checksums. It only asks the device to compute/verify. Am I missing your point? >> NVMe SSD can do the offload when the host sends the PRACT bit. But in >> the driver, this is tied to global integrity disablement using >> CONFIG_BLK_DEV_INTEGRITY. >> So, the idea is to introduce a bio flag REQ_INTEGRITY_OFFLOAD >> that the filesystem can send. The block-integrity and NVMe driver do >> the rest to make the offload work. >>