Re: OOMs on PS3 since kernel 6.9-rc4

[Johannes Weiner <hannes@cmpxchg.org>]

Hello Damian,

On Thu, Sep 26, 2024 at 09:00:25AM +0200, Damian Dudycz wrote:
> Johannes,
> 
> I have tested this with compaction enabled and it seems to be working fine now.
> I think, in that case, this should be enabled in ps3_defconfig by default.

I'm glad to hear it's working again!

> As for not having compaction in previous versions - I have been using this for pretty long
> time and Im pretty sure it used to work fine without it. Still I understand, that it should have been
> used, just mentioning that it really did work without this before that version.

Yes, it's a real regression and I believe you that it has worked until
now. My comment about luck was more in reference to the level of
support, testing and attention this configuration is getting:

config COMPACTION
        bool "Allow for memory compaction"
        default y
        select MIGRATION
        depends on MMU
        help
          Compaction is the only memory management component to form
          high order (larger physically contiguous) memory blocks
          reliably. The page allocator relies on compaction heavily and
          the lack of the feature can lead to unexpected OOM killer
          invocations for high order memory requests. You shouldn't
          disable this option unless there really is a strong reason for
          it and then we would be really interested to hear about that at
          linux-mm@kvack.org.

So I definitely agree that the ps3_defconfig should be fixed.

> I’ll let ps3_defconfig maintainer know about compaction missing in ps3_defconfig
> or send patch for that config myself.

Thanks, yes this makes sense. This should be a good list of pointers:

hannes@column ~/src/linux/linux $ ./scripts/get_maintainer.pl -f arch/powerpc/configs/ps3_defconfig 
Michael Ellerman <mpe@ellerman.id.au> (supporter:LINUX FOR POWERPC (32-BIT AND 64-BIT),commit_signer:2/2=100%)
Nicholas Piggin <npiggin@gmail.com> (reviewer:LINUX FOR POWERPC (32-BIT AND 64-BIT))
Christophe Leroy <christophe.leroy@csgroup.eu> (reviewer:LINUX FOR POWERPC (32-BIT AND 64-BIT))
Naveen N Rao <naveen@kernel.org> (reviewer:LINUX FOR POWERPC (32-BIT AND 64-BIT))
Geoff Levand <geoff@infradead.org> (commit_signer:2/2=100%,authored:2/2=100%,added_lines:1/1=100%,removed_lines:1/1=100%)
linuxppc-dev@lists.ozlabs.org (open list:LINUX FOR POWERPC (32-BIT AND 64-BIT))
linux-kernel@vger.kernel.org (open list)

Johannes