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:
> > > > > If lvm2 thinp is enabled in kdump, lvm2-monitor.service is
> > > > > monitor and autoextend the size of thin pool. Otherwise the
> > > > > dumped to a no-enough-space target will be incomplete and unable
> > > > > further analysis.
> > > > >
> > > > > In this patch, lvm2-monitor.service will be started before
> > > > > .service for 2nd kernel, then be stopped in kdump post.d phase.
> > > > > the thin pool monitoring and size-autoextend can be ensured
> > > > >
> > > > > Signed-off-by: Tao Liu <ltao(a)redhat.com>
> > > > > ---
> > > > > dracut-lvm2-monitor.service | 15 +++++++++++++++
> > > > > dracut-module-setup.sh | 16 ++++++++++++++++
> > > > > kexec-tools.spec | 2 ++
> > > > > 3 files changed, 33 insertions(+)
> > > > > create mode 100644 dracut-lvm2-monitor.service
> > > > >
> > > > > diff --git a/dracut-lvm2-monitor.service
> > > > This seems to be a copy of /lib/systemd/system/lvm2-monitor.service.
> > > > Wondering if we can dirctly include that file in initramfs when
> > > > image. But I am fuzzy on details of dracut implementation. It has
> > > > too long since I played with it. So Bao and kdump team will be best
> > > > to comment on this.
> > > >
> > > This is quite interesting - monitoring should in fact never be started
> > > wthin 'ramdisk' so I'm acutlly wondering what is this service
> > > there.
> > >
> > > Design was to start 'monitoring' of devices just after switch to
> > > since running 'dmeventd' out of ramdisk does not make any sense
> > Hi Zdenek,
> > In case of kdump, we save core dump from initramfs context and reboot
> > back into primary kernel. And that's why this need of dm monitoring (
> > and thin pool auto extension) working from inside the initramfs
> > context.
> So IMHO this although does not look like the best approach. AFAIK the
> lvm.conf within ramdisk is also a modified version.
> It looks like there should be a better alternative - like 'after'
> checking there is 'enough' room in thin-pool for use with thinLV - should
> be 'computable' and in case the size is not good enough - try to extend
> thin-pool prior use/mount of thinLV (size of space in thin-pool %DATA &
> %METATDATA and occupancy of %DATA thinLV could be obtained by 'lvs' tool)
One potential problem here is that we don't know what's the size of
vmcore in advance. It gets filtered and saved and we dont know in
advance, how many kernel pages will be there.
Is that still right, Bao?
Yes, it's still right.
We have features in makedumpfile to estimate the expected disk space for
vmcore dumping. E.g System RAM is 2TB, makedumpfile running tells 256GB
disk space is needed for storing vmcore, by filtering out zero pages,
unused pages, etc. However, that estimation is done in 1st kernel, and
the running kernel could dynamically allocate pages. So the estimation
can only give very rough data, in magnitude level. E.g you have 1TB
memory, while the disk space is only 200GB, that's obviously not enough.
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
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.