* Re: [PATCH v3] mm: migrate: requeue destination folio on deferred split queue [not found] ` <20260312175241.01b876f3b325264f43312d79@linux-foundation.org> @ 2026-03-13 10:40 ` Usama Arif 2026-03-14 22:40 ` Andrew Morton 0 siblings, 1 reply; 5+ messages in thread From: Usama Arif @ 2026-03-13 10:40 UTC (permalink / raw) To: Andrew Morton, SeongJae Park Cc: npache, david, ziy, willy, linux-mm, matthew.brost, joshua.hahnjy, hannes, rakie.kim, byungchul, gourry, ying.huang, apopple, linux-kernel, kernel-team, richard.weiyang, stable On 13/03/2026 03:52, Andrew Morton wrote: > On Thu, 12 Mar 2026 17:16:30 -0700 SeongJae Park <sj@kernel.org> 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 <hannes@cmpxchg.org> >>> 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. I have CC-ed stable@vger.kernel.org to this email. Should I resend the patch with CC stable in commit message? ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v3] mm: migrate: requeue destination folio on deferred split queue 2026-03-13 10:40 ` [PATCH v3] mm: migrate: requeue destination folio on deferred split queue Usama Arif @ 2026-03-14 22:40 ` Andrew Morton 2026-03-15 0:05 ` SeongJae Park 0 siblings, 1 reply; 5+ messages in thread From: Andrew Morton @ 2026-03-14 22:40 UTC (permalink / raw) To: Usama Arif Cc: SeongJae Park, npache, david, ziy, willy, linux-mm, matthew.brost, joshua.hahnjy, hannes, rakie.kim, byungchul, gourry, ying.huang, apopple, linux-kernel, kernel-team, richard.weiyang, stable On Fri, 13 Mar 2026 13:40:29 +0300 Usama Arif <usama.arif@linux.dev> wrote: > > > On 13/03/2026 03:52, Andrew Morton wrote: > > On Thu, 12 Mar 2026 17:16:30 -0700 SeongJae Park <sj@kernel.org> 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 <hannes@cmpxchg.org> > >>> 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? If we can't identify any benefit to userspace then I don't think this patch meets the criteria for backporting. > I have CC-ed stable@vger.kernel.org to this email. Should I resend the patch > with CC stable in commit message? That's OK, I update changelogs. A lot. ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v3] mm: migrate: requeue destination folio on deferred split queue 2026-03-14 22:40 ` Andrew Morton @ 2026-03-15 0:05 ` SeongJae Park 2026-03-15 0:23 ` Andrew Morton 0 siblings, 1 reply; 5+ messages in thread From: SeongJae Park @ 2026-03-15 0:05 UTC (permalink / raw) To: Andrew Morton Cc: SeongJae Park, Usama Arif, npache, david, ziy, willy, linux-mm, matthew.brost, joshua.hahnjy, hannes, rakie.kim, byungchul, gourry, ying.huang, apopple, linux-kernel, kernel-team, richard.weiyang, stable On Sat, 14 Mar 2026 15:40:42 -0700 Andrew Morton <akpm@linux-foundation.org> wrote: > On Fri, 13 Mar 2026 13:40:29 +0300 Usama Arif <usama.arif@linux.dev> wrote: > > > > > > > On 13/03/2026 03:52, Andrew Morton wrote: > > > On Thu, 12 Mar 2026 17:16:30 -0700 SeongJae Park <sj@kernel.org> 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 <hannes@cmpxchg.org> > > >>> 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 [...] ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v3] mm: migrate: requeue destination folio on deferred split queue 2026-03-15 0:05 ` SeongJae Park @ 2026-03-15 0:23 ` Andrew Morton 2026-03-20 11:41 ` David Hildenbrand (Arm) 0 siblings, 1 reply; 5+ messages in thread From: Andrew Morton @ 2026-03-15 0:23 UTC (permalink / raw) To: SeongJae Park Cc: Usama Arif, npache, david, ziy, willy, linux-mm, matthew.brost, joshua.hahnjy, hannes, rakie.kim, byungchul, gourry, ying.huang, apopple, linux-kernel, kernel-team, richard.weiyang, stable On Sat, 14 Mar 2026 17:05:54 -0700 SeongJae Park <sj@kernel.org> wrote: > 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. That'll do, thanks ;) Pasted, added cc:stable. It's been there since 6.12 so I don't see a need to rush this in, so I won't move this into mm-hotfixes - it'll go into mainline for 7.1-rc1 after which -stable should pick it up. ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v3] mm: migrate: requeue destination folio on deferred split queue 2026-03-15 0:23 ` Andrew Morton @ 2026-03-20 11:41 ` David Hildenbrand (Arm) 0 siblings, 0 replies; 5+ messages in thread From: David Hildenbrand (Arm) @ 2026-03-20 11:41 UTC (permalink / raw) To: Andrew Morton, SeongJae Park Cc: Usama Arif, npache, ziy, willy, linux-mm, matthew.brost, joshua.hahnjy, hannes, rakie.kim, byungchul, gourry, ying.huang, apopple, linux-kernel, kernel-team, richard.weiyang, stable On 3/15/26 01:23, Andrew Morton wrote: > On Sat, 14 Mar 2026 17:05:54 -0700 SeongJae Park <sj@kernel.org> wrote: > >> 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. > > That'll do, thanks ;) > > Pasted, added cc:stable. It's been there since 6.12 so I don't see a > need to rush this in, so I won't move this into mm-hotfixes - it'll go > into mainline for 7.1-rc1 after which -stable should pick it up. Makes sense. I guess using the partially-mapped is only a slight problem, because we usually try to split partially-mapped before migrating. So it's mostly about over-allocated THPs (mostly 0) not getting scanned and split+reclaimed after they were migrated. Under memory pressure without swap, that might create a user-visible problem, especially when many such THPs are migrated before being scanned for zeropages that can be reclaimed. -- Cheers, David ^ permalink raw reply [flat|nested] 5+ messages in thread
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2026-03-13 10:40 ` [PATCH v3] mm: migrate: requeue destination folio on deferred split queue Usama Arif
2026-03-14 22:40 ` Andrew Morton
2026-03-15 0:05 ` SeongJae Park
2026-03-15 0:23 ` Andrew Morton
2026-03-20 11:41 ` David Hildenbrand (Arm)
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