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Thu, 23 May 2024 16:02:24 +0900 (KST) Received: from nj.shetty?samsung.com (unknown [107.99.41.245]) by epsmtip2.samsung.com (KnoxPortal) with ESMTPA id 20240523070220epsmtip27aba71b0cc2f5f6b9888de9ca58d5e0e~SDCA-AENl3101731017epsmtip2E; Thu, 23 May 2024 07:02:20 +0000 (GMT) Date: Thu, 23 May 2024 06:55:14 +0000 From: Nitesh Shetty To: Bart Van Assche Cc: Jens Axboe , Jonathan Corbet , Alasdair Kergon , Mike Snitzer , Mikulas Patocka , Keith Busch , Christoph Hellwig , Sagi Grimberg , Chaitanya Kulkarni , Alexander Viro , Christian Brauner , Jan Kara , martin.petersen@oracle.com, david@fromorbit.com, hare@suse.de, damien.lemoal@opensource.wdc.com, anuj20.g@samsung.com, joshi.k@samsung.com, nitheshshetty@gmail.com, gost.dev@samsung.com, Vincent Fu , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, dm-devel@lists.linux.dev, linux-nvme@lists.infradead.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH v20 12/12] null_blk: add support for copy offload Message-ID: <20240523065514.7745whk3pwem57cy@nj.shetty@samsung.com> MIME-Version: 1.0 In-Reply-To: <631c55b9-8b0a-4ac0-81bd-acf82c4a7602@acm.org> X-Brightmail-Tracker: H4sIAAAAAAAAA02TfUxTVxjGc+69vb1V0SuiOxbdoHNRYUA7W3Zg4owK3ATdWOZY4sxYR69A KG3txxxsThRBwQjC5pQCCq0ZFhAEqmIV53Cg8hG2ISKKVrHddFWpMjWGCWu9dfG/3/vx5Dnn ffNSuP9xvpBKV+lZrUquFJFTiOPnFi8Mu3L/gw3iAyWzUWNXJ4627XmOo7rrxSRynXsE0I/u ZzhynN0B0HhvH46snTcAqjJVEmjo7EkMnTaVYshS14Gh8n25GOqYvE+i0vbLADkHjBhquxqK qvMPEeh020UC9dsqSHTwJycf1ZyfwFDJzgEMtTq2AtTgGiXQhauB6PaunQD1PT/PWz6P6b+U wHSZIHPSeJ3P9N1oIpj+XgPTXFtAMi2HtjB3WsoAc2ooh2TMRd/zmN25D0jmZJ6dxzx0XiWY 0TMDJFNkrQVMT9Wv/MRZ6zKWprFyBasNYlUpakW6KjVGlPBx8spkWaRYEiaJQu+KglTyTDZG tGp1YlhcutIzIVHQV3KlwZNKlOt0oohlS7Vqg54NSlPr9DEiVqNQaqSacJ08U2dQpYarWH20 RCx+R+Zp/CIjrdl9i9C4pn/tfGLn54DhaYVAQEFaCguqy4lCMIXyp08BaG/vxrjgEYCmX/7h ebv86ScAWpv0LxWmUjPgmtoAnBjcg3PBGIDuEbNHQVEE/Ra8uz3UiyQdCrsnKa82gF4En9ys eeGG0xdIWN9wCfMWZtGxsLijhu9lP3olHDySz+N4JrxY5iC8LKDfg86nLRj3iD8F8P6zFRyv gnf+tZEcz4J/n7fyORbCsQdtvvwmaPnhMOk1hvR2AI2DRsAV3od5XcW4l3E6DT7O7/WJ58O9 XQ0Yl58Od487fMZ+sPXAS34T1jdW+QzmwstPt/qYgfc6nb4J9WJw34FdYA943fjKh4yv+HEc DQvc23gcvwFzj5XjRs/wcDoQ1kxQHC6GjbaIKkDWgrmsRpeZyupkmiUqdtP/C09RZzaDFwcU ktAKRm66w9sBRoF2AClcFOD3mWXNBn8/hTwrm9Wqk7UGJatrBzLPrkpw4ewUtecCVfpkiTRK LI2MjJRGLYmUiF7zc+VVKvzpVLmezWBZDat9qcMogTAHMzQkPpxZa98gpuYQdb/ZJ1TrscMr oq998+2SEavb1blj2sJFObK7l/HyZXOSjnxiqW6xk/Ode9MP1m92FLkXJNkOVfSckA4P35MP vr0xcDSvrv67rLN1U6+3ln5ZPc9dOZA6fFsomOzosZwQPNXGJ80JNi+fGjwkevx7g+lo/Joz oY0jnxbbxgOOTS00fxRXVr7llivqZzr2c/9Y9ZkF+yaG9lIF8ZOPbjb2dsRfWSDOVqybn50c V0HGdx/rXzyjegZm7hFeO/pMtt+y+TgZ8scqV2512Gr+eGBSbd+iLLFhbO1fVkdsoTVz/3pt dsSHCWsTi0s2BjeZ8m8DcYrSqqvys+WLCF2aXBKCa3Xy/wBRiIfXyQQAAA== X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFmpileLIzCtJLcpLzFFi42LZdlhJXpfhlV+awb+lahbrTx1jtmia8JfZ YvXdfjaL14c/MVpM+/CT2eLJgXZGi99nzzNbbDl2j9FiwaK5LBY3D+xkstizaBKTxcrVR5ks Zk9vZrI4+v8tm8WkQ9cYLZ5encVksfeWtsXCtiUsFnv2nmSxuLxrDpvF/GVP2S2WH//HZDGx 4yqTxY4njYwW616/Z7E4cUva4nF3B6PF+b/HWR1kPC5f8fY4tUjCY+esu+we5+9tZPG4fLbU Y9OqTjaPzUvqPV5snsnosftmA5vH4r7JrB69ze/YPHa23mf1+Pj0FovH+31X2Tz6tqxi9Diz 4Ah7gHAUl01Kak5mWWqRvl0CV8ab/zYFf7grHvV0MDcwdnF1MXJySAiYSCyatJgRxBYS2M0o cfZ5EURcUmLZ3yPMELawxMp/z9m7GLmAaj4ySuxb28fWxcjBwSKgKvGyRRvEZBPQljj9nwOk XERAQ+Lbg+UsIOXMAmfYJM6t/Qc2X1jAVaL/6HJ2EJtXwFni+to2VoiZZ5kkrj3cApUQlDg5 8wkLiM0sYCYxb/NDZpAFzALSEsv/cUCE5SWat84Gu41TwFri6ffNTBMYBWch6Z6FpHsWQvcs JN0LGFlWMUqmFhTnpucWGxYY5qWW6xUn5haX5qXrJefnbmIEJxMtzR2M21d90DvEyMTBeIhR goNZSYQ3eqVvmhBvSmJlVWpRfnxRaU5q8SFGaQ4WJXFe8Re9KUIC6YklqdmpqQWpRTBZJg5O qQYmRaUzR2Yd3qp+u8xqc7q0yJ9SUZ2Dxqdtbl0qzrDnnKXMULDxRmmxba33rmbTiYGLo6oe Hr0reTbp2oVHGRvjr6QoX9TedyrZ6mmncup8uXmlJfnWPpFbar+8mvmns2qKLoNP75Tvoic+ X/iz+dyfwM9HeJ0EHm5bm6C7+JTVr9nsXLc7L87PvD39IDvPYvV32XWN+x3UvroXOPBxx3mn xLr7Rug0SzBY3/jUH2DgzVP5b2VApPimTz/v7Di2aL0BE8/Slqymog6tbwvfuN5nXN+66cej lpWxrV139mxZOoXvy7wlL1flCh87/D/Ii9Eh/pNWRadvsf+NIrWQhynbHzJOSVG0fXT6hzLj phxrJZbijERDLeai4kQA8kXBwJUDAAA= X-CMS-MailID: 20240523070224epcas5p3e695021dfef14e09478bef71d4bb64ff X-Msg-Generator: CA Content-Type: multipart/mixed; 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format="flowed" Content-Transfer-Encoding: 8bit Content-Disposition: inline On 22/05/24 10:52AM, Bart Van Assche wrote: >On 5/21/24 07:46, Nitesh Shetty wrote: >>On 20/05/24 04:42PM, Bart Van Assche wrote: >>>On 5/20/24 03:20, Nitesh Shetty wrote: >>>>+    __rq_for_each_bio(bio, req) { >>>>+        if (seg == blk_rq_nr_phys_segments(req)) { >>>>+            sector_in = bio->bi_iter.bi_sector; >>>>+            if (rem != bio->bi_iter.bi_size) >>>>+                return status; >>>>+        } else { >>>>+            sector_out = bio->bi_iter.bi_sector; >>>>+            rem = bio->bi_iter.bi_size; >>>>+        } >>>>+        seg++; >>>>+    } >>> >>>_rq_for_each_bio() iterates over the bios in a request. Does a copy >>>offload request always have two bios - one copy destination bio and >>>one copy source bio? If so, is 'seg' a bio counter? Why is that bio >>>counter compared with the number of physical segments in the request? >>> >>Yes, your observation is right. We are treating first bio as dst and >>second as src. If not for that comparision, we might need to store the >>index in a temporary variable and parse based on index value. > >I'm still wondering why 'seg' is compared with blk_rq_nr_phys_segments(req). > In this case blk_rq_nr_phys_segments is used as counter value(==2), which tells its a src IO. But using a macro instead of this comparison will avoid this confusion. We will change this in next version to make it explicit. Thank you, Nitesh Shetty ------0ARpVfROdpzmGW4Ln12FwIta42jNjH8le_L8dBWq-uMGoSqN=_1f5f7_ Content-Type: text/plain; charset="utf-8" ------0ARpVfROdpzmGW4Ln12FwIta42jNjH8le_L8dBWq-uMGoSqN=_1f5f7_--