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

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

On Thu, Jul 23, 2026 at 05:02:49PM -0700, Andrew Morton wrote:
> On Thu, 23 Jul 2026 16:17:51 +0200 "Vlastimil Babka (SUSE)" <vbabka@kernel.org> wrote:
> 
> > > 2/4 actually came after 4/4 during development. Without it, compaction
> > > cannot make sufficient forward progress on the promoted non-movable
> > > requests. So it is a hard functional requirement.
> > 
> > So that's the tricky part then. If it's a hard functional requirement for
> > 4/4 and yet leaving it out results in no conflicts when applying 3/4 and 4/4
> > (as it indeed seems so, based on my local test), then it's quite possible
> > stable folks will figure out themselves they need 3/4 as a stable-dep-off:
> > 4/4 but won't backport 2/4, unless you act quickly enough on their mails.
> > 
> > > Whether it deserves an independent Fixes: depends on how many
> > > GFP_KERNEL pageblock_order requests we have :-) I'm guessing not many.
> > 
> > I don't know how else to indicate it though. It's kind of a co-fix with 4/4?
> > 
> > >> > (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.
> > > 
> > > Yes, I *think* it should work with tagging just 4/4.
> > > 
> > > It won't apply cleanly or build without 3/4. So I'd assume if that
> > > dependency is lost, the automated backport will bounce and I can send
> > > a backport series by hand.
> > 
> > The way I see if often happen is that Greg sends a mail that it bounced and
> > soon after Sasha replies with fixed up version/series. Which could very
> > easily be 3/4 + 4/4 without 2/4.
> 
> My brain hurts.  I'll include
> 
> Fixes: e3aa7df331bc ("mm: page_alloc: defrag_mode")
> Cc: <stable@vger.kernel.org>
> 
> in all four patches.

Thank you!  Don't make us "figure it out" as that way lies struggles and
time delays and the huge chance I get it wrong.  Tagging them all
ensures none of this happens and it all "just works".

thanks,

greg k-h