Weirdness with discard cmd and get log pages

[Nisha Miller]

Hi Keith,

thank you for the test case. I'll try it out.

My problem is that I need to make it work on Kernel 2.6.33. For now,
since blkdiscard and fstrim send only 1 range I'm ok with current
support for discard cmd.

However I need to fix the issue for get log pages. Are there any known
issues with mapping user buffers in older linux-nvme drivers?

thanks
Nisha


On Fri, Oct 14, 2016 at 10:44 AM, Keith Busch <keith.busch at intel.com> wrote:
> On Thu, Oct 13, 2016 at 07:18:09PM -0400, Keith Busch wrote:
>> On Thu, Oct 13, 2016 at 11:18:43AM -0700, Nisha Miller wrote:
>> > Yes, that is what I noticed too. I used the nvme-cli command like this:
>> >
>> > nvme dsm /dev/nvme0n1 -a 0,0,0,0 --blocks=4,5,6,7 --slbs=100,200,300,400 --ad
>> >
>> > This turns up as nvme_user_cmd in the driver, which calls
>> > nvme_map_user_pages to setup the SG list.
>>
>> Okay, that's what I use too. I'm not observing any issues on a 4.8 kernel
>> or back to 4.4 either. I've not tested 3.19 though, and the mechanism
>> it uses to map user buffers is completely different. Could you verify if
>> your observation exists in a more current stable release?
>
> Just for reference, this is how I've verified 64 ranges. My device
> deterministically returns 0 on any deallocated block, and is formatted
> with 512b LBAs.
>
>   # create a random 1MB file
>   dd if=/dev/urandom of=~/rand.1M.in bs=1M count=1
>
>   # write it to the device
>   dd if=~/rand.1M.in of=/dev/nvme0n1 oflag=direct
>
>   # read it back out
>   dd if=/dev/nvme0n1 of=~/rand.1M.out bs=1M count=1 iflag=direct
>
>   # compare the two to verify they're the same
>   diff ~/rand.1M.in ~/rand.1M.out
>
>   # write a bunch of 0-filled 8k holes in the original file
>   for i in $(seq 0 2 127); do dd if=/dev/zero of=~/rand.1M.in bs=8k seek=$i conv=notrunc count=1 2> /dev/null; done
>
>   # deallocate the exact same ranges as the file's new 0-filled holes
>   nvme dsm /dev/nvme0n1 -d --slbs=`seq 0 32 2016 | tr "\n" "," | sed "s/,$//g"` --blocks=`printf "16,%0.s" {0..63} | sed "s/,$//g"`
>
>   # read the file from the device
>   dd if=/dev/nvme0n1 of=~/rand.1M.out bs=1M count=1 iflag=direct
>
>   # verify the contents are still the same
>   diff ~/rand.1M.in ~/rand.1M.out
>
> Works for me.