linux-kernel - Re: [PATCH v2] powerpc/pseries/cmm: fix managed page counts when migrating pages between zones

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Date:   Wed, 18 Dec 2019 15:05:11 +1100 (AEDT)
From:   Michael Ellerman <patch-notifications@...erman.id.au>
To:     David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org
Cc:     David Hildenbrand <david@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Richard Fontana <rfontana@...hat.com>, linux-mm@...ck.org,
        Paul Mackerras <paulus@...ba.org>,
        Arun KS <arunks@...eaurora.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linuxppc-dev@...ts.ozlabs.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2] powerpc/pseries/cmm: fix managed page counts when migrating pages between zones

On Mon, 2019-12-16 at 10:30:58 UTC, David Hildenbrand wrote:
> Commit 63341ab03706 (virtio-balloon: fix managed page counts when migrati=
> ng
> pages between zones) fixed a long existing BUG in the virtio-balloon
> driver when pages would get migrated between zones.  I did not try to
> reproduce on powerpc, but looking at the code, the same should apply to
> powerpc/cmm ever since it started using the balloon compaction
> infrastructure (luckily just recently).
> 
> In case we have to migrate a ballon page to a newpage of another zone, th=
> e
> managed page count of both zones is wrong. Paired with memory offlining
> (which will adjust the managed page count), we can trigger kernel crashes
> and all kinds of different symptoms.
> 
> Fix it by properly adjusting the managed page count when migrating if
> the zone changed.
> 
> We'll temporarily modify the totalram page count. If this ever becomes a
> problem, we can fine tune by providing helpers that don't touch
> the totalram pages (e.g., adjust_zone_managed_page_count()).
> 
> Fixes: fe030c9b85e6 ("powerpc/pseries/cmm: Implement balloon compaction")
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Richard Fontana <rfontana@...hat.com>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Arun KS <arunks@...eaurora.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: linuxppc-dev@...ts.ozlabs.org
> Signed-off-by: David Hildenbrand <david@...hat.com>

Applied to powerpc fixes, thanks.

https://git.kernel.org/powerpc/c/e352f576d345e5bf1fb62c8559851448a6c1d9cd

cheers