Re: cache on SSD makes system unresponsive

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On 21. okt. 2017 04:55, Mike Snitzer wrote:
On Thu, Oct 19 2017 at  5:59pm -0400,
Oleg Cherkasov <o1e9@member.fsf.org> wrote:

On 19. okt. 2017 21:09, John Stoffel wrote:


So aside from SAR outout: you don't have any system logs?  Or a vmcore
of the system (assuming it crashed?) -- in it you could access the
kernel log (via 'log' command in crash utility.

Unfortunately no logs. I have tried to see if I may recover dmesg however no luck. All logs but the latest dmesg boot are zeroed. Of course there are messages, secure and others however I do not see any valuable information there.

System did not crash, OOM were going wind however I did manage to Ctrl-Alt-Del from the main console via iLO so eventually it rebooted with clean disk umount.


More specifics on the workload would be useful.  Also, more details on
the LVM cache configuration (block size?  writethrough or writeback?
etc).

No extra params but specifying mode writethrough initially. Hardware RAID1 on cache disk is 64k and on main array hardware RAID5 128k.

I had followed precisely documentation from RHEL doc site so lvcreate, lvconvert to update type and then lvconvert to add cache.

I have decided to try writeback after and shifted cachemode to it with lvcache.


I'll be looking very closely for any sign of memory leaks (both with
code inspection and testing while kemmleak is enabled).

But the more info you can provide on the workload the better.

According to SAR there are no records about 20min before I reboot, so I suspect SAR daemon failed a victim of OOM.

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