Hannes, While you are working on the feature code, is there a sequence of system commands I can use ?
thanks, Pankaj On Mon, May 14, 2018 at 1:53 PM, Mike Snitzer <[email protected]> wrote: > On Mon, May 14 2018 at 12:13pm -0400, > Mike Snitzer <[email protected]> wrote: > > > On Sun, May 13 2018 at 8:47pm -0400, > > Pankaj Agarwal <[email protected]> wrote: > > > > > Hi, > > > How do i set the nr_request value for LV's as it's not writable > like other > > > drives on a linux system. > > > LV's are set as dm-0 and dm-1 on my system. > > > #cat /sys/block/dm-0/queue/nr_requests > > > 128 > > > # echo 256 > /sys/block/dm-0/queue/nr_requests > > > -bash: echo: write error: Invalid argument > > > > In the block layer, bio-based devices cannot have their nr_requests > > changed, see: block/blk-sysfs.c:queue_requests_store() > > > > So any bio-based DM device (e.g. linear target) won't be allowed to > > change nr_requests. > > > > The only way to change this would be from the bottom up: > > 1) change the underlying request-based device(s) (e.g. /dev/sda) > > 2) dmsetup suspend + dmsetup resume any bio-based DM device(s) that are > > stacked ontop of the request-based device(s) you changed in 1) > > -- this will restack the queue_limits from the bottom up; so the DM > > device will then reflect the underlying devices' limits. > > I was mistaken. DM core (in the kernel) will only restack the > queue_limits (nr_requests included) if a new DM table is loaded. > > So a simple suspend+resume will _not_ change the bio-based DM device's > queue_limits: > > [root@thegoat ~]# lsblk /dev/nullb0 > NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT > nullb0 253:0 0 250G 0 disk > └─foo 252:0 0 250G 0 dm > [root@thegoat ~]# cat /sys/block/nullb0/queue/nr_requests > 128 > [root@thegoat ~]# cat /sys/block/dm-0/queue/nr_requests > 128 > [root@thegoat ~]# echo 64 > /sys/block/nullb0/queue/nr_requests > [root@thegoat ~]# cat /sys/block/nullb0/queue/nr_requests > 64 > [root@thegoat ~]# cat /sys/block/dm-0/queue/nr_requests > 128 > [root@thegoat ~]# dmsetup suspend foo > [root@thegoat ~]# dmsetup resume foo > [root@thegoat ~]# cat /sys/block/dm-0/queue/nr_requests > 128 > > There was some related work started in this area by Hannes (now cc'd) > during LSF last month. He added a chain-notifier to DM devices so that > if any underlying devices (devices referenced in a DM device's table) > were changed then the enture device stack would have its limits > reloaded. > > Not sure where Hannes ended up with that. Would love to get it polished > now and staged for 4.18 inclusion. > > Hannes? >
_______________________________________________ linux-lvm mailing list [email protected] https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
