Dne 01. 06. 22 v 14:51 Vivek Goyal napsal(a):
On Mon, May 30, 2022 at 11:28:42AM +0200, Zdenek Kabelac wrote:
Dne 30. 05. 22 v 4:34 Baoquan He napsal(a):
On 05/27/22 at 11:39am, Vivek Goyal wrote:
On Fri, May 27, 2022 at 04:59:38PM +0200, Zdenek Kabelac wrote:
Dne 27. 05. 22 v 16:50 Vivek Goyal napsal(a):
On Fri, May 27, 2022 at 04:42:25PM +0200, Zdenek Kabelac wrote: > Dne 27. 05. 22 v 14:20 Vivek Goyal napsal(a): >> On Fri, May 27, 2022 at 02:45:14PM +0800, Tao Liu wrote: >>
Technically speaking, one could first run makedumpfile to just determine what will be size of vmcore and then actually save vmcore in second round. But that will double the filtering time.
Yeah. Besides, memory content of system is changing dynamically all the time. E.g your oracle DB is running or not running, the user space data is defintely not the same. And two times of work need involve people's manual work, automation is still expected if can be made.
Running very resource hungry dmeventd (looks all the process memory in RAM
- could be many many MB) in kdump environment is not IMHO worst option
here - I'd prefer to avoid execution of dmeventd in this ramfs image.
I understand. We also want to keep the size of kdump initramfs to the minimum.
Right.
I talked to Tao, he tested on kvm guest with 500M memory and 100M disk space to trigger the insufficient disk space usage. Tao said the dmeventd will cosume about 40MB when executing. I am not familiar with dmeventd, if its running will cost about constant 40M memory, no matter how much disk space need be extended at one time, we can adjust our kdump script to increase the default crashkernel= value if lvm2 thinp is detected. It looks acceptable in kdump side.
Dmeventd runs in 'mlockall()' mode - so the whole executable with all libraries and all the memory allocations are pinned in RAM (so IMHO 40MiB is way small number)
Reason for this is - in the normal 'running' mode lvm2 protects dmeventd from being blocked when it would run out of rootfs and it would suspend DM with rootfs on it - so by having the whole binary mlocked in RAM it cannot cause 'deadlock' waiting on itsefl when it suspends given DM device.
For kdump executional environment in ramdisk this is not really relevant condition (but dmeventd was not designed to be executed in such environment). However as mentioned in my previous post - it's actually more useful to run 'lvm lvextend --use-policies' with given thin-pool name in a plain shell parallel loop - as it basically gives same result with way less memory 'obstruction' and with far better control as well (i.e. leaving user a defined minimum to be sure it can actuall boot afterwards - so dumping only when there really is some space...)
Hi Zdenek,
Is running "lvm extend --use-policies"racy as well. I mean, it is possible that dump process fills up the pool before lvm extend gets a chance to extend it? Or it is fine even if thin pool gets full. Once it is extended again, it will unblock dumping process automatically?
This is the *very* same command dmeventd will run internally (with luxury of being locked in RAM).
By default there is 60sec 'delay' before thin-pool starts to 'reject' IO operation on overfilled thin-pool so it should not present any obstacle. Yeah - it might be slightly delayed before extension happens (depending on sleep value in shell loop)
But this still does not protect again filling up data LV completely and making rootfs unusable/unbootable.
It actually gives you some position where you can better 'estimate' whether you actually do want to kdump or not - by calculating kdump space and free space and ensuring there will be left some guaranteed free space (since you are the only user of thin-pool in this moment)
Bao mentioned that makedumpfile has capability to estimate the size of core dump. May be we should run that instead in second kernel, extend the thin pool accordingly and the ninitiate the dump. For
Yep - if you know how much data you want to store - and ensure there is enough free space in thin-pool to store them - it's the best case.
Regards
Zdenek