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Howlett" , Usama Arif , Kiryl Shutsemau , Vlastimil Babka , Kairui Song , Mikhail Zaslonko , Vasily Gorbik , Baolin Wang , Barry Song , Dev Jain , Lance Yang , Nico Pache , Ryan Roberts , cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 9/9] mm: switch deferred split shrinker to list_lru Date: Thu, 28 May 2026 00:08:05 -0700 Message-ID: <20260528070807.144064-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260527204757.2544958-10-hannes@cmpxchg.org> References: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Stat-Signature: togk7pyagt8nmb6bg15tjrouema6197m X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 2153B20008 X-HE-Tag: 1779952102-468498 X-HE-Meta: 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 jYTviy8a czvkeAhngapViqWs5YxUUXoR3Db9/ebpc5I2uWAKzpCMe4BUkLnszoTCdMUuIMlasc8aKHINthFUgVp2KeQ0HJ7X13OGJwlIV5Xtucm5uIMyIGAUGJmS8z3tjccS4Q+7mm1yTD30s5fG2d150eDde3EepykyoaBUN9SqASCOgepZNE9RopcGngWDQHQoHtveSpfNTymKEsoIuNnRqOKbezTIsbj/+CiU7Hp8ODNF3BzrP6mLfUCYd/+4ZQUFabWVdWS0H2S5EQjqQefA3XANv80PaNWHVQyrt/6JjjSNJyIWhmP6bE1Bdim6JE5BkoggWqSsS3jBJ+KBzkcr4nXhn6uvf3kGqUCeGmykL2TeHkx8+67KkoxIOp+VQ0hvKHJ9mqMYtVYWkdZD7RKnvOepcShw0jR8b2NiFG8TSGI4+OvROUhc= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Johannes, On Wed, 27 May 2026 16:45:16 -0400 Johannes Weiner wrote: > The deferred split queue handles cgroups in a suboptimal fashion. The > queue is per-NUMA node or per-cgroup, not the intersection. That means > on a cgrouped system, a node-restricted allocation entering reclaim > can end up splitting large pages on other nodes: > > alloc/unmap > deferred_split_folio() > list_add_tail(memcg->split_queue) > set_shrinker_bit(memcg, node, deferred_shrinker_id) > > for_each_zone_zonelist_nodemask(restricted_nodes) > mem_cgroup_iter() > shrink_slab(node, memcg) > shrink_slab_memcg(node, memcg) > if test_shrinker_bit(memcg, node, deferred_shrinker_id) > deferred_split_scan() > walks memcg->split_queue > > The shrinker bit adds an imperfect guard rail. As soon as the cgroup > has a single large page on the node of interest, all large pages owned > by that memcg, including those on other nodes, will be split. > > list_lru properly sets up per-node, per-cgroup lists. As a bonus, it > streamlines a lot of the list operations and reclaim walks. It's used > widely by other major shrinkers already. Convert the deferred split > queue as well. > > The list_lru per-memcg heads are instantiated on demand when the first > object of interest is allocated for a cgroup, by calling > folio_memcg_alloc_deferred(). Add calls to where splittable pages are > created: anon faults, swapin faults, khugepaged collapse. > > These calls create all possible node heads for the cgroup at once, so > the migration code (between nodes) doesn't need any special care. > > Reported-by: Mikhail Zaslonko > Tested-by: Mikhail Zaslonko > Acked-by: Shakeel Butt > Reviewed-by: Lorenzo Stoakes (Oracle) > Signed-off-by: Johannes Weiner > --- > include/linux/huge_mm.h | 7 +- > include/linux/memcontrol.h | 4 - > include/linux/mmzone.h | 12 -- > mm/huge_memory.c | 364 +++++++++++++------------------------ > mm/internal.h | 2 +- > mm/khugepaged.c | 5 + > mm/memcontrol.c | 12 +- > mm/memory.c | 4 + > mm/mm_init.c | 15 -- > mm/swap_state.c | 10 + > 10 files changed, 150 insertions(+), 285 deletions(-) > > diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h > index edece3e26985..f6c2531a27a3 100644 > --- a/include/linux/huge_mm.h > +++ b/include/linux/huge_mm.h > @@ -423,10 +423,10 @@ static inline int split_huge_page(struct page *page) > { > return split_huge_page_to_list_to_order(page, NULL, 0); > } > + > +int folio_memcg_alloc_deferred(struct folio *folio); > + > void deferred_split_folio(struct folio *folio, bool partially_mapped); > -#ifdef CONFIG_MEMCG > -void reparent_deferred_split_queue(struct mem_cgroup *memcg); > -#endif > > void __split_huge_pmd(struct vm_area_struct *vma, pmd_t *pmd, > unsigned long address, bool freeze); > @@ -664,7 +664,6 @@ static inline int folio_split(struct folio *folio, unsigned int new_order, > } > > static inline void deferred_split_folio(struct folio *folio, bool partially_mapped) {} > -static inline void reparent_deferred_split_queue(struct mem_cgroup *memcg) {} > #define split_huge_pmd(__vma, __pmd, __address) \ > do { } while (0) I found this patch is now in mm-new and it makes UM mode kunit fails like below. $ ./tools/testing/kunit/kunit.py run --kunitconfig mm/damon/tests/ [00:00:02] Configuring KUnit Kernel ... [00:00:02] Building KUnit Kernel ... Populating config with: $ make ARCH=um O=.kunit olddefconfig Building with: $ make all compile_commands.json scripts_gdb ARCH=um O=.kunit --jobs=8 ERROR:root:../mm/swap_state.c: In function ‘__swap_cache_alloc’: ../mm/swap_state.c:468:26: error: implicit declaration of function ‘folio_memcg_alloc_deferred’ [-Wimplicit-function-declaration] 468 | if (order > 1 && folio_memcg_alloc_deferred(folio)) { | ^~~~~~~~~~~~~~~~~~~~~~~~~~ make[4]: *** [../scripts/Makefile.build:289: mm/swap_state.o] Error 1 make[4]: *** Waiting for unfinished jobs.... make[3]: *** [../scripts/Makefile.build:548: mm] Error 2 make[3]: *** Waiting for unfinished jobs.... make[2]: *** [/home/lkhack/linux/Makefile:2143: .] Error 2 make[1]: *** [/home/lkhack/linux/Makefile:248: __sub-make] Error 2 make: *** [Makefile:248: __sub-make] Error 2 Maybe we can define the function for CONFIG_TRANSPARENT_HUGEPAGE unset case? I confirmed the below attaching temporal fix works for at least kunit. Thanks, SJ [...] === >8 === >From 23b5800dd49085707baee5774b74782c3e424f24 Mon Sep 17 00:00:00 2001 From: SeongJae Park Date: Wed, 27 May 2026 23:58:07 -0700 Subject: [PATCH] mm/huge_mm: define memcg_alloc_deferred() for !CONFIG_TRANSPARENT_HUGEPPAGE MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Without this, UM mode kunit fails like below. $ ./tools/testing/kunit/kunit.py run --kunitconfig mm/damon/tests/ [00:00:02] Configuring KUnit Kernel ... [00:00:02] Building KUnit Kernel ... Populating config with: $ make ARCH=um O=.kunit olddefconfig Building with: $ make all compile_commands.json scripts_gdb ARCH=um O=.kunit --jobs=8 ERROR:root:../mm/swap_state.c: In function ‘__swap_cache_alloc’: ../mm/swap_state.c:468:26: error: implicit declaration of function ‘folio_memcg_alloc_deferred’ [-Wimplicit-function-declaration] 468 | if (order > 1 && folio_memcg_alloc_deferred(folio)) { | ^~~~~~~~~~~~~~~~~~~~~~~~~~ make[4]: *** [../scripts/Makefile.build:289: mm/swap_state.o] Error 1 make[4]: *** Waiting for unfinished jobs.... make[3]: *** [../scripts/Makefile.build:548: mm] Error 2 make[3]: *** Waiting for unfinished jobs.... make[2]: *** [/home/lkhack/linux/Makefile:2143: .] Error 2 make[1]: *** [/home/lkhack/linux/Makefile:248: __sub-make] Error 2 make: *** [Makefile:248: __sub-make] Error 2 Fix by implementing the function for CONFIG_TRANSPARENT_HUGEPPAGE unset case. Fixes: https://lore.kernel.org/20260527204757.2544958-10-hannes@cmpxchg.org Signed-off-by: SeongJae Park --- include/linux/huge_mm.h | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h index f6c2531a27a35..055de7b8ed487 100644 --- a/include/linux/huge_mm.h +++ b/include/linux/huge_mm.h @@ -663,6 +663,11 @@ static inline int folio_split(struct folio *folio, unsigned int new_order, return -EINVAL; } +static inline int folio_memcg_alloc_deferred(struct folio *folio) +{ + return 0; +} + static inline void deferred_split_folio(struct folio *folio, bool partially_mapped) {} #define split_huge_pmd(__vma, __pmd, __address) \ do { } while (0) -- 2.47.3