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Date: Mon, 06 Jan 2020 22:24:09 -0500 From: "Martin K. Petersen" <martin.petersen@...cle.com> To: Kirill Tkhai <ktkhai@...tuozzo.com> Cc: "Martin K. Petersen" <martin.petersen@...cle.com>, axboe@...nel.dk, linux-block@...r.kernel.org, linux-kernel@...r.kernel.org, linux-ext4@...r.kernel.org, tytso@....edu, adilger.kernel@...ger.ca, ming.lei@...hat.com, osandov@...com, jthumshirn@...e.de, minwoo.im.dev@...il.com, damien.lemoal@....com, andrea.parri@...rulasolutions.com, hare@...e.com, tj@...nel.org, ajay.joshi@....com, sagi@...mberg.me, dsterba@...e.com, chaitanya.kulkarni@....com, bvanassche@....org, dhowells@...hat.com, asml.silence@...il.com Subject: Re: [PATCH RFC 1/3] block: Add support for REQ_OP_ASSIGN_RANGE operation Kirill, Sorry, the holiday break got in the way. > But I also worry about NOFALLBACK case. There are possible block > devices, which support write zeroes, but they can't allocate blocks > (block allocation are just not appliable for them, say, these are all > ordinary hdd). Correct. We shouldn't go down this path unless a device is thinly provisioned (i.e. max_discard_sectors > 0). > But won't it be a good thing to return EOPNOTSUPP right from > __blkdev_issue_write_zeroes() in case of block device can't allocate > blocks (q->limits.write_zeroes_can_allocate in the patch below)? Here > is just a way to underline block devices, which support write zeroes, > but allocation of blocks is meant nothing for them (wasting of time). I don't like "write_zeroes_can_allocate" because that makes assumptions about WRITE ZEROES being the command of choice. I suggest we call it "max_allocate_sectors" to mirror "max_discard_sectors". I.e. put emphasis on the semantic operation and not the plumbing. -- Martin K. Petersen Oracle Linux Engineering
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