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b=MY1AnAUxfwcQXbJahppa/QPFx5OTh/brWeAoHYP9rwTwng2qRv2gB9kMvjK74eLO1 ONC9/gFP/+fVkmffi70Fp6+v1duqh6n9na+awJ4WZvH0TRCtiB2Pni2/xgo4DhLKwX eXz5ISXerrxMLy+fxHAl/DRSaYiocrFyqAdR9IduFyxhtNVbPUUCVRnBp6y6TmafKJ S1S9pWh74towQZ9qeHlYIvVBI8EeRyJYzH694U4TPlGY1WZlLLxcP3Xc/wQxgVVNqT O0P8zcrWdSggXxoYdFgVeNmPk7eD8R9CL45uFcAA+g3pofFyeLR4wSsWcOM3Mxl5q3 D3pgpF8xrytDQ== From: SeongJae Park To: Andrew Morton Cc: SeongJae Park , Usama Arif , npache@redhat.com, david@kernel.org, ziy@nvidia.com, willy@infradead.org, linux-mm@kvack.org, matthew.brost@intel.com, joshua.hahnjy@gmail.com, hannes@cmpxchg.org, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com, linux-kernel@vger.kernel.org, kernel-team@meta.com, richard.weiyang@gmail.com, stable@vger.kernel.org Subject: Re: [PATCH v3] mm: migrate: requeue destination folio on deferred split queue Date: Sat, 14 Mar 2026 17:05:54 -0700 Message-ID: <20260315000555.76876-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260314154042.327ba957b1a8c10f64ae0169@linux-foundation.org> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 032431C000B X-Stat-Signature: hbrmgrqf6iwk4g6i577sxfjfu5xp6983 X-Rspam-User: X-HE-Tag: 1773533169-840724 X-HE-Meta: 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 Hbdll62U WX6uVFvbcU1gsi4/T7n4T+du6Xjm1+Q52DuSJ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sat, 14 Mar 2026 15:40:42 -0700 Andrew Morton wrote: > On Fri, 13 Mar 2026 13:40:29 +0300 Usama Arif wrote: > > > > > > > On 13/03/2026 03:52, Andrew Morton wrote: > > > On Thu, 12 Mar 2026 17:16:30 -0700 SeongJae Park wrote: > > > > > >>> By the time migrate_folio_move() runs, partially mapped folios without a > > >>> pin have already been split by migrate_pages_batch(). So only two cases > > >>> remain on the deferred list at this point: > > >>> 1. Partially mapped folios with a pin (split failed). > > >>> 2. Fully mapped but potentially underused folios. > > >>> The recorded partially_mapped state is forwarded to deferred_split_folio() > > >>> so that the destination folio is correctly re-queued in both cases. > > >>> > > >>> Reported-by: Johannes Weiner > > >>> Fixes: dafff3f4c850 ("mm: split underused THPs") > > >> > > >> Seems the commit is merged in 6.12. And I assume the user impact on > > >> THP-shrinker enabled systems is visible. If so, should we Cc stable@ ? > > > > > > I think the user impact should be visible to backport, but the > > > changelog is elusive on details? > > > > > > > > > The original patches added THPs to deferred_list at fault/collapse, they > > got removed but not added back to the list after migration. > > This patch adds them to the deferred_list on migration. The user would > > not expect the THPs to get removed from deferred_list on migration, so > > this fixes user expectations. > > Maybe users just won't notice? My guess of the user-visible consequence was like following. Because THPs are removed from the deferred_list, THP shinker cannot split the underutilized THPs in time. As a result, users will show less free memory than before. I believe I might be wrong and Usama can correct me in the case. Thanks, SJ [...]