Re: Regression in Linux 5.5.0-rc[1-5]: btrfs send/receive out of memory

[Craig Andrews <candrews@integralblue.com>]

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On 2020-01-13 09:48, Craig Andrews wrote:
> On 2020-01-13 08:37, David Sterba wrote:
>> On Mon, Jan 13, 2020 at 07:41:13AM -0500, Craig Andrews wrote:
>>> If I perform a btrfs send receive like so:
>>> 
>>> sh -c btrfs send -p /mnt/everything/.snapshots/root.20191230
>>> /mnt/everything/.snapshots/root.20191231 | btrfs receive
>>> /mnt/backup/.snapshots/
>>> 
>>> On Linux 5.4.0, the process completes successfully.
>>> 
>>> Starting with Linux 5.5.0-rc1 up to the current 5.5 rc, 5.5.0-rc5, 
>>> the
>>> result is the OOM killer being invoked which (among other process
>>> carnage) kills the btrfs processes stopping the backup.
>> 
>> As this is on the -rc1, it's possible that changes done in the MM
>> subsystem could change the logic of OOM and that send now is able to
>> trigger the OOM.
>> 
>> There are 2 btrfs patches in send.c but they reduce amount of work,
>> namely for heavily reflinked extents so the effects should be 
>> opposite.
>> 
>> To find out where's the cause, is it possible that you build a kernel
>> from the 5.4-based branch and run the send again? It's the same set of
>> btrfs patches that gets merged to 5.5.
>> 
>> From repository: 
>> git://git.kernel.org/pub/scm/linux/kernel/git/kdave/linux.git
>> branch: for-5.5-rc4
>> 
>> If this can't be done we'll find another way to debug it.
> 
> I've grabbed, compiled, and installed the kernel. I'll be able to tell
> you the results of running the test tomorrow at about this time.
> 

I couldn't get the kernel to boot so I need to spend more time on that.

Is there any info I can get that would be helpful using my current 
kernels (either 5.4 or 5.5.0-rc5) while I work out why I can't boot the 
kernel you linked me to?

Thanks,
~Craig

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