Dne 27. 05. 22 v 17:39 Vivek Goyal napsal(a):
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 needed
for
>>>>> monitor and autoextend the size of thin pool. Otherwise the vmcore
>>>>> dumped to a no-enough-space target will be incomplete and unable for
>>>>> further analysis.
>>>>>
>>>>> In this patch, lvm2-monitor.service will be started before
kdump-capture
>>>>> .service for 2nd kernel, then be stopped in kdump post.d phase. So
>>>>> the thin pool monitoring and size-autoextend can be ensured during
kdump.
>>>>>
>>>>> 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
b/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
generating
>>>> image. But I am fuzzy on details of dracut implementation. It has been
>>>> 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
file doing
>>> there.
>>>
>>> Design was to start 'monitoring' of devices just after switch to
'rootfs' -
>>> since running 'dmeventd' out of ramdisk does not make any sense at
all.
>> 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' activation
> 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?
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.
You could likely 'stream/buffer' these kdump data in form of i.e. '4MiB ~
128MiB' chunks (or any other suitable size which will be 'quick enough) and
before each new write of such chunk just compare there is enough free space in
thin-pool with lvs - should be still better then running 'dmeventd' in the
background - and gives you also the best control over the deadlock in case
you run completely out-of-space (i.e. leaving enough room in thin-pool and
avoiding full dump so user could still 'boot')
Since you will be only a single user of thinLV in initramfs - this should be
reasonable straigforward to achieve.
Regards
Zdenek