[linux-lvm] when bringing dm-cache online, consumes all memory and reboots

[Joe Thornber]

On Sun, Mar 22, 2020 at 10:57:35AM -0700, Scott Mcdermott wrote:
> have a 931.5 GibiByte SSD pair in raid1 (mdraid) as cache LV for a
> data LV on 1.8 TebiByte raid1 (mdraid) pair of larger spinning disk.
> these disks are hosted by a small 4GB big.little ARM system
> running4.4.192-rk3399 (armbian 5.98 bionic).  parameters were set
> with: lvconvert --type cache --cachemode writeback --cachepolicy smq
> --cachesettings migration_threshold=10000000

If you crash then the cache assumes all blocks are dirty and performs
a full writeback.  You have set the migration_threshold extremely high
so I think this writeback process is just submitting far too much io at once.

Bring it down to around 2048 and try again.

- Joe