On Mon, Mar 23, 2020 at 1:26 AM Joe Thornber <thornber@xxxxxxxxxx> wrote: > On Sun, Mar 22, 2020 at 10:57:35AM -0700, Scott Mcdermott wrote: > > [system crashed, uses all memory when brought online...] > > 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. the device wasn't visible in "dmsetup table" prior to activation, so I tried: lvchange -ay raidbak4/bakvol4; dmsetup message raidbak4-bakvol4 0 migration_threshold 204800 but this continued to crash, apparently the value used at activation time is enough to crash the system. instead using: lvchange --cachesettings migration_threshold=204800 raidbak4/bakvol4 lvchange -ay raidbak4/bakvol4 it worked, and the used disk bandwidth was much lower (which, I don't want it to be, but a functioning system is needed for the thing to work at all). after some time doing a lot of I/Os, it went silent and is presumably flushed, seems to be in working order, thanks. so I have to experiment to find the highest migration_threshold value that won't crash my system with OOM? I don't want there to be any cache bandwidth restriction, it should saturate and use all available to aggressively promote (for my frequent case, working set actually would fit entirely in cache, but it's ok if the cache learns this slowly from usage). seems like I should be able to use a value that means "use all available bandwidth" that isn't going to take down my system with OOM. even if I play with the value, I might find during some pathological circumstance, it pushes beyond where I tested and now it crashes my system again. is there some safe calculation I can use to determine the maximum amount? _______________________________________________ linux-lvm mailing list linux-lvm@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
