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Thu, 23 Jul 2026 07:08:19 -0700 (PDT) Date: Thu, 23 Jul 2026 10:08:15 -0400 From: Johannes Weiner To: "Vlastimil Babka (SUSE)" Cc: Andrew Morton , Greg Kroah-Hartman , Sasha Levin , Suren Baghdasaryan , Michal Hocko , Brendan Jackman , Zi Yan , David Hildenbrand , Lorenzo Stoakes , "Liam R . Howlett" , Mike Rapoport , Shakeel Butt , linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v2 4/4] mm: page_alloc: fix non-movable reclaim storm in defrag_mode Message-ID: References: <20260722150006.3848560-1-hannes@cmpxchg.org> <20260722150006.3848560-5-hannes@cmpxchg.org> <20260722162207.31a2c491ffaf36d1e8948c14@linux-foundation.org> <67e1219e-9d47-4a30-a8dd-fdcf03229f58@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <67e1219e-9d47-4a30-a8dd-fdcf03229f58@kernel.org> X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 9B4C84000F X-Stat-Signature: hrgg6sorxts9qo7xrpofcza7ahucmf8e X-HE-Tag: 1784815701-404804 X-HE-Meta: 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 ZHHmsW25 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Jul 23, 2026 at 12:22:58PM +0200, Vlastimil Babka (SUSE) wrote: > + Greg and Sasha > > On 7/23/26 01:22, Andrew Morton wrote: > > On Wed, 22 Jul 2026 10:56:47 -0400 Johannes Weiner wrote: > > > >> > >> Fixes: e3aa7df331bc ("mm: page_alloc: defrag_mode") > >> Cc: > >> Signed-off-by: Johannes Weiner > > > > 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. Yes. Only 1/4 could be argued away. 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. Whether it deserves an independent Fixes: depends on how many GFP_KERNEL pageblock_order requests we have :-) I'm guessing not many. > > (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.