From 98bd3af0bb6bfdb0fb39cbfa05456acb374b691e Mon Sep 17 00:00:00 2001 From: "Lorenzo Stoakes (ARM)" Date: Thu, 30 Jul 2026 11:55:48 +0100 Subject: mm/huge_memory: separate out CONFIG_PERSISTENT_HUGE_ZERO_FOLIO logic Rather than mixing the refcounted and non-refcounted CONFIG_PERSISTENT_HUGE_ZERO_FOLIO logic, separate the two out cleanly so it is clear what happens when this configuration option is set and what happens when it is not. Introduce HUGE_ZERO_UNSET_PFN to abstract the ~0UL assignment, only introduce the refcount, lock and shrinker if !CONFIG_PERSISTENT_HUGE_ZERO_FOLIO, abstract initialisation and teardown, abstract the huge zero folio allocation from refcounting. Also change a BUG_ON() to WARN_ON_ONCE() while we're at it. No functional change intended. Link: https://lore.kernel.org/20260730-fix-refcounted-huge-zero-v2-2-c5d8a41b317f@kernel.org Signed-off-by: Lorenzo Stoakes (ARM) Fixes: 3b77e8c8cde5 ("mm/thp: make is_huge_zero_pmd() safe and quicker") Cc: Baolin Wang Cc: Barry Song Cc: David Hildenbrand (Arm) Cc: Dev Jain Cc: Hannes Reinecke Cc: Hengbin Zhang Cc: Hugh Dickins Cc: Kiryl Shutsemau Cc: Lance Yang Cc: Liam R. Howlett Cc: Nico Pache Cc: Pankaj Raghav Cc: Ryan Roberts Cc: Yang Shi Cc: Zi Yan Cc: Signed-off-by: Andrew Morton --- mm/huge_memory.c | 160 ++++++++++++++++++++++++++++++++----------------------- 1 file changed, 94 insertions(+), 66 deletions(-) diff --git a/mm/huge_memory.c b/mm/huge_memory.c index f43852ef9944..f84fe7913d88 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -78,10 +78,15 @@ static unsigned long deferred_split_scan(struct shrinker *shrink, struct shrink_control *sc); static bool split_underused_thp = true; +#define HUGE_ZERO_UNSET_PFN (~0UL) +struct folio *huge_zero_folio __read_mostly; +unsigned long huge_zero_pfn __read_mostly = HUGE_ZERO_UNSET_PFN; +#ifndef CONFIG_PERSISTENT_HUGE_ZERO_FOLIO static atomic_t huge_zero_refcount; static DEFINE_SPINLOCK(huge_zero_lock); -struct folio *huge_zero_folio __read_mostly; -unsigned long huge_zero_pfn __read_mostly = ~0UL; +static struct shrinker *huge_zero_folio_shrinker; +#endif + unsigned long huge_anon_orders_always __read_mostly; unsigned long huge_anon_orders_madvise __read_mostly; unsigned long huge_anon_orders_inherit __read_mostly; @@ -223,23 +228,58 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma, return orders; } -static bool get_huge_zero_folio(void) +static struct folio *alloc_huge_zero_folio(void) { struct folio *zero_folio; - /* Paired with atomic_set_release(). */ - if (likely(atomic_inc_not_zero(&huge_zero_refcount))) - return true; - zero_folio = folio_alloc((GFP_TRANSHUGE | __GFP_ZERO | __GFP_ZEROTAGS) & ~__GFP_MOVABLE, HPAGE_PMD_ORDER); if (!zero_folio) { count_vm_event(THP_ZERO_PAGE_ALLOC_FAILED); - return false; + return NULL; + } + folio_clear_large_rmappable(zero_folio); /* Explicitly not rmappable. */ + return zero_folio; +} + +#ifdef CONFIG_PERSISTENT_HUGE_ZERO_FOLIO +static int __init huge_zero_init(void) +{ + huge_zero_folio = alloc_huge_zero_folio(); + if (!huge_zero_folio) { + pr_warn("Allocating persistent huge zero folio failed\n"); + } else { + huge_zero_pfn = folio_pfn(huge_zero_folio); + count_vm_event(THP_ZERO_PAGE_ALLOC); } - /* Ensure zero folio won't have large_rmappable flag set. */ - folio_clear_large_rmappable(zero_folio); + return 0; +} + +static void __init huge_zero_shrinker_exit(void) +{ +} + +struct folio *mm_get_huge_zero_folio(struct mm_struct *mm) +{ + return huge_zero_folio; +} + +void mm_put_huge_zero_folio(struct mm_struct *mm) +{ +} +#else +static bool get_huge_zero_folio(void) +{ + struct folio *zero_folio; + + /* Paired with atomic_set_release(). */ + if (likely(atomic_inc_not_zero(&huge_zero_refcount))) + return true; + + zero_folio = alloc_huge_zero_folio(); + if (unlikely(!zero_folio)) + return false; /* Paired with critical section in shrink_huge_zero_folio_scan(). */ spin_lock(&huge_zero_lock); @@ -266,33 +306,7 @@ static void put_huge_zero_folio(void) * Counter should never go to zero here. Only shrinker can put * last reference. */ - BUG_ON(atomic_dec_and_test(&huge_zero_refcount)); -} - -struct folio *mm_get_huge_zero_folio(struct mm_struct *mm) -{ - if (IS_ENABLED(CONFIG_PERSISTENT_HUGE_ZERO_FOLIO)) - return huge_zero_folio; - - if (mm_flags_test(MMF_HUGE_ZERO_FOLIO, mm)) - return READ_ONCE(huge_zero_folio); - - if (!get_huge_zero_folio()) - return NULL; - - if (mm_flags_test_and_set(MMF_HUGE_ZERO_FOLIO, mm)) - put_huge_zero_folio(); - - return READ_ONCE(huge_zero_folio); -} - -void mm_put_huge_zero_folio(struct mm_struct *mm) -{ - if (IS_ENABLED(CONFIG_PERSISTENT_HUGE_ZERO_FOLIO)) - return; - - if (mm_flags_test(MMF_HUGE_ZERO_FOLIO, mm)) - put_huge_zero_folio(); + WARN_ON_ONCE(atomic_dec_and_test(&huge_zero_refcount)); } static unsigned long shrink_huge_zero_folio_count(struct shrinker *shrink, @@ -316,14 +330,53 @@ static unsigned long shrink_huge_zero_folio_scan(struct shrinker *shrink, zero_folio = huge_zero_folio; VM_WARN_ON_ONCE(!zero_folio); WRITE_ONCE(huge_zero_folio, NULL); - WRITE_ONCE(huge_zero_pfn, ~0UL); + WRITE_ONCE(huge_zero_pfn, HUGE_ZERO_UNSET_PFN); } folio_put(zero_folio); return HPAGE_PMD_NR; } -static struct shrinker *huge_zero_folio_shrinker; +static int __init huge_zero_init(void) +{ + huge_zero_folio_shrinker = shrinker_alloc(0, "thp-zero"); + if (!huge_zero_folio_shrinker) { + shrinker_free(deferred_split_shrinker); + list_lru_destroy(&deferred_split_lru); + return -ENOMEM; + } + + huge_zero_folio_shrinker->count_objects = shrink_huge_zero_folio_count; + huge_zero_folio_shrinker->scan_objects = shrink_huge_zero_folio_scan; + shrinker_register(huge_zero_folio_shrinker); + return 0; +} + +static void __init huge_zero_shrinker_exit(void) +{ + shrinker_free(huge_zero_folio_shrinker); +} + +struct folio *mm_get_huge_zero_folio(struct mm_struct *mm) +{ + if (mm_flags_test(MMF_HUGE_ZERO_FOLIO, mm)) + return READ_ONCE(huge_zero_folio); + + if (!get_huge_zero_folio()) + return NULL; + + if (mm_flags_test_and_set(MMF_HUGE_ZERO_FOLIO, mm)) + put_huge_zero_folio(); + + return READ_ONCE(huge_zero_folio); +} + +void mm_put_huge_zero_folio(struct mm_struct *mm) +{ + if (mm_flags_test(MMF_HUGE_ZERO_FOLIO, mm)) + put_huge_zero_folio(); +} +#endif /* CONFIG_PERSISTENT_HUGE_ZERO_FOLIO */ #ifdef CONFIG_SYSFS static ssize_t enabled_show(struct kobject *kobj, @@ -987,39 +1040,14 @@ static int __init thp_shrinker_init(void) deferred_split_shrinker->scan_objects = deferred_split_scan; shrinker_register(deferred_split_shrinker); - if (IS_ENABLED(CONFIG_PERSISTENT_HUGE_ZERO_FOLIO)) { - /* - * Bump the reference of the huge_zero_folio and do not - * initialize the shrinker. - * - * huge_zero_folio will always be NULL on failure. We assume - * that get_huge_zero_folio() will most likely not fail as - * thp_shrinker_init() is invoked early on during boot. - */ - if (!get_huge_zero_folio()) - pr_warn("Allocating persistent huge zero folio failed\n"); - return 0; - } - - huge_zero_folio_shrinker = shrinker_alloc(0, "thp-zero"); - if (!huge_zero_folio_shrinker) { - shrinker_free(deferred_split_shrinker); - list_lru_destroy(&deferred_split_lru); - return -ENOMEM; - } - - huge_zero_folio_shrinker->count_objects = shrink_huge_zero_folio_count; - huge_zero_folio_shrinker->scan_objects = shrink_huge_zero_folio_scan; - shrinker_register(huge_zero_folio_shrinker); - - return 0; + return huge_zero_init(); } static void __init thp_shrinker_exit(void) { - shrinker_free(huge_zero_folio_shrinker); shrinker_free(deferred_split_shrinker); list_lru_destroy(&deferred_split_lru); + huge_zero_shrinker_exit(); } static int __init hugepage_init(void) -- cgit v1.2.3