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Subject: Re: Linux 5.13-rc6 regression to 5.12.x: kernel OOM and panic during
 kernel boot in low memory Xen VM's (256MB assigned memory).
To:     Sander Eikelenboom <linux@eikelenboom.it>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Juergen Gross <jgross@suse.com>
Cc:     linux-kernel <linux-kernel@vger.kernel.org>,
        "xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>,
        kernel test robot <oliver.sang@intel.com>
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 <9108c22e-3521-9e24-6124-7776d947b788@rasmusvillemoes.dk>
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 <7338064f-10b6-545d-bc6c-843d04aafe28@eikelenboom.it>
 <e7f9c4f8-1669-75ce-b052-1030350a159e@eikelenboom.it>
From:   Rasmus Villemoes <linux@rasmusvillemoes.dk>
Message-ID: <bfdd1d6b-77a3-450b-71f4-63e9cc314ace@rasmusvillemoes.dk>
Date:   Mon, 21 Jun 2021 18:54:00 +0200
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On 18/06/2021 03.06, Sander Eikelenboom wrote:
> On 17/06/2021 21:39, Sander Eikelenboom wrote:

> 
> OK, done some experimentation and it seems with 256M assigned to the VM
> it was almost at the edge of OOM with the 5.12 kernel as well in the
> config I am using it.
> With v5.12 when I assign 240M it boots, with 230M it doesn't. With 5.13
> the tipping point seems to be around 265M and 270M, so my config was
> already quite close to the edge.
> 
> The "direct kernel boot" feature I'm using just seems somewhat memory
> hungry, but using another compression algorithm for the kernel and
> initramfs already helped in my case.
> 
> So sorry for the noise, clearly user-error.

Hm, perhaps, but I'm still a bit nervous about that report from Oliver
Sang/kernel test robot, which was for a VM equipped with 16G of memory.
But despite quite a few attempts, I haven't been able to reproduce that
locally, so unfortunately I have no idea what's going on.

Rasmus