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Wed, 13 Jul 2022 20:34:16 +0900 (KST) Received: from epsmtrp2.samsung.com (unknown [182.195.40.14]) by epcas5p3.samsung.com (KnoxPortal) with ESMTPA id 20220713113415epcas5p3ebffdbb62e1ec75e91fddb55a349bb01~BYFTi17KU1019810198epcas5p3J; Wed, 13 Jul 2022 11:34:15 +0000 (GMT) Received: from epsmgms1p1new.samsung.com (unknown [182.195.42.41]) by epsmtrp2.samsung.com (KnoxPortal) with ESMTP id 20220713113415epsmtrp2705cca99a2e2583cf1ed427b270b4bca~BYFThs_6R2637826378epsmtrp2Y; Wed, 13 Jul 2022 11:34:15 +0000 (GMT) X-AuditID: b6c32a49-885ff700000025be-98-62ceadb83bcb Received: from epsmtip1.samsung.com ( [182.195.34.30]) by epsmgms1p1new.samsung.com (Symantec Messaging Gateway) with SMTP id 0A.66.08905.7BDAEC26; Wed, 13 Jul 2022 20:34:15 +0900 (KST) Received: from test-zns (unknown [107.110.206.5]) by epsmtip1.samsung.com (KnoxPortal) with ESMTPA id 20220713113413epsmtip1962effb45ddc119218799b3a3c3e60a1~BYFR7ek5_0690606906epsmtip1N; Wed, 13 Jul 2022 11:34:13 +0000 (GMT) Date: Wed, 13 Jul 2022 16:58:50 +0530 From: Kanchan Joshi To: Sagi Grimberg Cc: hch@lst.de, kbusch@kernel.org, axboe@kernel.dk, io-uring@vger.kernel.org, linux-nvme@lists.infradead.org, linux-block@vger.kernel.org, asml.silence@gmail.com, joshiiitr@gmail.com, anuj20.g@samsung.com, gost.dev@samsung.com Subject: Re: [PATCH for-next 4/4] nvme-multipath: add multipathing for uring-passthrough commands Message-ID: <20220713112850.GD30733@test-zns> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFlrHJsWRmVeSWpSXmKPExsWy7bCmhu6OteeSDBo+C1g0TfjLbDFn1TZG i9V3+9ksbh7YyWSxcvVRJot3redYLM6/PcxkMenQNUaLvbe0LeYve8puse71exYHbo+ds+6y e5y/t5HF4/LZUo9NqzrZPDYvqffYfbOBzaNvyypGj8+b5AI4orJtMlITU1KLFFLzkvNTMvPS bZW8g+Od403NDAx1DS0tzJUU8hJzU22VXHwCdN0yc4DOVFIoS8wpBQoFJBYXK+nb2RTll5ak KmTkF5fYKqUWpOQUmBToFSfmFpfmpevlpZZYGRoYGJkCFSZkZ9y4o1CwiL9i2cwmxgbGYzxd jJwcEgImEo9e/GLsYuTiEBLYzSjx99IPKOcTo8T+t+uZIZxvjBI3m64zwrQs2jeTFSKxl1Gi 8dkmqKpnjBI7F/5mAaliEVCVWPx3ClAVBwebgKbEhcmlIKaIgIrEmze5IOXMAi8YJRbOW8gK Ui4skCyx6ckkJhCbV0BXon//aVYIW1Di5MwnYCM5BewlPs34zgZiiwooSxzYdpwJZJCEwFoO iVNff0Jd5yKx5nUXG4QtLPHq+BZ2CFtK4vO7vVDxZIlLM88xQdglEo/3HISy7SVaT/Uzg9jM ApkS6ya1skHYfBK9v58wgTwgIcAr0dEmBFGuKHFv0lNWCFtc4uGMJVC2h8TH+c3skDD5yyzx qPEc4wRGuVlI/pmFZAWEbSXR+aGJdRbQCmYBaYnl/zggTE2J9bv0FzCyrmKUTC0ozk1PLTYt MMxLLYfHcXJ+7iZGcMLV8tzBePfBB71DjEwcjIcYJTiYlUR4/5w9lSTEm5JYWZValB9fVJqT WnyI0RQYPROZpUST84EpP68k3tDE0sDEzMzMxNLYzFBJnNfr6qYkIYH0xJLU7NTUgtQimD4m Dk6pBqau84knW5L/RW76UXxAIcv/4wKNW/sLlbRfT3VIO3pTzORmUdLrrwHll48rSJ2Wzot6 YJb08d06ExHRBcfMXNb/n7g2ZNFSppx/0pJTA7e3z/K3jrcNenbeuejeV7kFFdZXXwrc08mf yLLqo6yHl/GjglB5kYXHd5rPeC346gxbafCdZ2dmXErbK/NSTSTrzJFUqdqiXE7losaDtoXJ K278P7LMrELBOE2+YN6hWZ+eaGc9qWI68njGOp3fJY3cz/5Gr4u51WJ7v6NMsSH0L6tWymyV 3Z0ch6P2s/4qmJY1NzM540fFzGVnLE8qvm5by7yvWdx76+fsCY4cKdaX1PgFC6+7NzByXH4z wUnojasSS3FGoqEWc1FxIgA8sd4CQQQAAA== X-Brightmail-Tracker: H4sIAAAAAAAAA+NgFvrDLMWRmVeSWpSXmKPExsWy7bCSnO72teeSDJbuE7domvCX2WLOqm2M Fqvv9rNZ3Dywk8li5eqjTBbvWs+xWJx/e5jJYtKha4wWe29pW8xf9pTdYt3r9ywO3B47Z91l 9zh/byOLx+WzpR6bVnWyeWxeUu+x+2YDm0ffllWMHp83yQVwRHHZpKTmZJalFunbJXBlXNr0 mqXgIk/FrdPTWBoY+7m6GDk5JARMJBbtm8naxcjFISSwm1Fi+4XdzBAJcYnmaz/YIWxhiZX/ noPZQgJPGCXWtyWD2CwCqhKL/04BaubgYBPQlLgwuRTEFBFQkXjzJhdkJLPAC0aJi1e2sICU CwskS2x6MokJxOYV0JXo338aau9fZok356axQCQEJU7OfAJmMwuYSczb/JAZZCizgLTE8n8c IGFOAXuJTzO+s4HYogLKEge2HWeawCg4C0n3LCTdsxC6FzAyr2KUTC0ozk3PLTYsMMxLLdcr TswtLs1L10vOz93ECI4gLc0djNtXfdA7xMjEwXiIUYKDWUmE98/ZU0lCvCmJlVWpRfnxRaU5 qcWHGKU5WJTEeS90nYwXEkhPLEnNTk0tSC2CyTJxcEo1MJlqvW790G2vfmyd3vprMVMctaNC n5U9sDnQp7evra02Mu97kOzK25+NrjHvXiK04U1icWDHozccD7yK356Qd646aviYsTLhwgOH csEZ3dKXdugxLioJSE+KT2w31fqi35J3f5143sWrzlvbu+OkeKae7lX0Ohixylvpf5sWg7rZ xYNHJ+gtWPZz696Sd/d3PxG6kbDz1pGsnYEFcsFq07I/b/mu6TwvbNH/iSmPF+pfLmWbaXdS IedM45KrDLWC6SyNZ3iyjb+VLVYr2sfp1Xw7fc9Ch0Vi5f/XbvvkybrynjLP8Sa/dy32s/J4 d9s28YTO+PZwVqhzlGgze1JgwHZnn26dd45uftvfyl/dpsRSnJFoqMVcVJwIADW4z8kPAwAA X-CMS-MailID: 20220713113415epcas5p3ebffdbb62e1ec75e91fddb55a349bb01 X-Msg-Generator: CA Content-Type: multipart/mixed; boundary="----jllqsR28.5W1KdEnZlWKzx60EIuo6gwqBUS1IW9J_3KKio4g=_128281_" CMS-TYPE: 105P DLP-Filter: Pass X-CFilter-Loop: Reflected X-CMS-RootMailID: 20220711110827epcas5p3fd81f142f55ca3048abc38a9ef0d0089 References: <20220711110155.649153-1-joshi.k@samsung.com> <20220711110155.649153-5-joshi.k@samsung.com> <3fc68482-fb24-1f39-5428-faa3a8db9ecb@grimberg.me> <20220711183746.GA20562@test-zns> <5f30c7de-03b1-768a-d44f-594ed2d1dc75@grimberg.me> <20220712042332.GA14780@test-zns> <3a2b281b-793b-b8ad-6a27-138c89a46fac@grimberg.me> <20220713053757.GA15022@test-zns> Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org ------jllqsR28.5W1KdEnZlWKzx60EIuo6gwqBUS1IW9J_3KKio4g=_128281_ Content-Type: text/plain; charset="utf-8"; format="flowed" Content-Disposition: inline On Wed, Jul 13, 2022 at 12:03:48PM +0300, Sagi Grimberg wrote: > >>>However io_kiocb is less >>>constrained, and could be used as a context to hold such a space. >>> >>>Even if it is undesired to have io_kiocb be passed to uring_cmd(), it >>>can still hold a driver specific space paired with a helper to obtain it >>>(i.e. something like io_uring_cmd_to_driver_ctx(ioucmd) ). Then if the >>>space is pre-allocated it is only a small memory copy for a stable copy >>>that would allow a saner failover design. >> >>I am thinking along the same lines, but it's not about few bytes of >>space rather we need 80 (72 to be precise). Will think more, but >>these 72 bytes really stand tall in front of my optimism. > >You don't have to populate this space on every I/O, you can just >populate it when there is no usable path and when you failover a >request... Getting the space and when/how to populate it - related but diferent topics in this context. It is about the lifetime of SQE which is valid only for the first submission. If we don't make the command stable at that point, we don't have another chance. And that is exactly what happens for failover. Since we know IO is failed only when it fails, but by that time original passthrough-command is gone out of hand. I think if we somehow get the space (preallocated), it is ok to copy to command for every IO in mpath case. The other part (no usuable path) is fine, because we hit that condition during initial submission and therefore have the chance to allocate/copy the passthrough command. This patch already does that. ------jllqsR28.5W1KdEnZlWKzx60EIuo6gwqBUS1IW9J_3KKio4g=_128281_ Content-Type: text/plain; charset="utf-8" ------jllqsR28.5W1KdEnZlWKzx60EIuo6gwqBUS1IW9J_3KKio4g=_128281_--