Re: [PATCH v2 4/4] mm: page_alloc: fix non-movable reclaim storm in defrag_mode

["Vlastimil Babka (SUSE)" <vbabka@kernel.org>]

+ Greg and Sasha

On 7/23/26 01:22, Andrew Morton wrote:
> On Wed, 22 Jul 2026 10:56:47 -0400 Johannes Weiner <hannes@cmpxchg.org> wrote:
> 
>> 
>> Fixes: e3aa7df331bc ("mm: page_alloc: defrag_mode")
>> Cc: <stable@vger.kernel.org>
>> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
> 
> This cc:stable fix doesn't apply to current mainline because the
> preceding non-cc:stable patches get in the way.
> 
> This means that the -stable maintainers will have to ask you to redo
> the fix to make it backportable.  And you'll then be preparing a patch
> which hasn't had standalone testing in mainline.  All very cumbersome.

Or they backport the whole series, even if only 4/4 has a Fixes: tag.

> So is it practical to make the fix come first, as a cc:stable hotfix so
> we can upstream the other patches in the next merge window?

I think it can't come first, it's simply a complex fix that can't be done in
a single patch that would be reviewable. 3/4 is certainly a strict
dependency. I'm not sure if 2/4 as well. Perhaps 2/4 does deserve a Fixes:
tag and Cc: stable on its own, as it also fixes a defrag_mode deficiency.

> (An alternative would be to put cc:stable on all four patches.  That's
> a bit abusive but we do it rarely).

I don't think it's necessary, the stable team are quite capable of figuring
out the deps and backporting them with a Stable-dep-off: tag. IIRC the
"fake" tagging is discouraged? Maybe they can clarify.

> Either way, I'll get these into mm.git for testing while we await
> review on [4/4], thanks.
>