On Wed, Mar 9, 2022 at 3:48 PM Yu Zhao <yuzhao@xxxxxxxxxx> wrote: > > Add /sys/kernel/mm/lru_gen/enabled as a kill switch. Components that > can be disabled include: > 0x0001: the multi-gen LRU core > 0x0002: walking page table, when arch_has_hw_pte_young() returns > true > 0x0004: clearing the accessed bit in non-leaf PMD entries, when > CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG=y > [yYnN]: apply to all the components above > E.g., > echo y >/sys/kernel/mm/lru_gen/enabled > cat /sys/kernel/mm/lru_gen/enabled > 0x0007 > echo 5 >/sys/kernel/mm/lru_gen/enabled > cat /sys/kernel/mm/lru_gen/enabled > 0x0005 > > NB: the page table walks happen on the scale of seconds under heavy > memory pressure, in which case the mmap_lock contention is a lesser > concern, compared with the LRU lock contention and the I/O congestion. > So far the only well-known case of the mmap_lock contention happens on > Android, due to Scudo [1] which allocates several thousand VMAs for > merely a few hundred MBs. The SPF and the Maple Tree also have > provided their own assessments [2][3]. However, if walking page tables > does worsen the mmap_lock contention, the kill switch can be used to > disable it. In this case the multi-gen LRU will suffer a minor > performance degradation, as shown previously. > > Clearing the accessed bit in non-leaf PMD entries can also be > disabled, since this behavior was not tested on x86 varieties other > than Intel and AMD. > > [1] https://source.android.com/devices/tech/debug/scudo > [2] https://lore.kernel.org/lkml/20220128131006.67712-1-michel@xxxxxxxxxxxxxx/ > [3] https://lore.kernel.org/lkml/20220202024137.2516438-1-Liam.Howlett@xxxxxxxxxx/ > > Signed-off-by: Yu Zhao <yuzhao@xxxxxxxxxx> > Acked-by: Brian Geffon <bgeffon@xxxxxxxxxx> > Acked-by: Jan Alexander Steffens (heftig) <heftig@xxxxxxxxxxxxx> > Acked-by: Oleksandr Natalenko <oleksandr@xxxxxxxxxxxxxx> > Acked-by: Steven Barrett <steven@xxxxxxxxxxxx> > Acked-by: Suleiman Souhlal <suleiman@xxxxxxxxxx> > Tested-by: Daniel Byrne <djbyrne@xxxxxxx> > Tested-by: Donald Carr <d@xxxxxxxxxxxxxxx> > Tested-by: Holger Hoffstätte <holger@xxxxxxxxxxxxxxxxxxxxxx> > Tested-by: Konstantin Kharlamov <Hi-Angel@xxxxxxxxx> > Tested-by: Shuang Zhai <szhai2@xxxxxxxxxxxxxxxx> > Tested-by: Sofia Trinh <sofia.trinh@edi.works> > Tested-by: Vaibhav Jain <vaibhav@xxxxxxxxxxxxx> > --- > include/linux/cgroup.h | 15 +- > include/linux/mm_inline.h | 12 +- > include/linux/mmzone.h | 9 ++ > kernel/cgroup/cgroup-internal.h | 1 - > mm/Kconfig | 6 + > mm/vmscan.c | 237 +++++++++++++++++++++++++++++++- > 6 files changed, 271 insertions(+), 9 deletions(-) > > diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h > index 75c151413fda..b145025f3eac 100644 > --- a/include/linux/cgroup.h > +++ b/include/linux/cgroup.h > @@ -432,6 +432,18 @@ static inline void cgroup_put(struct cgroup *cgrp) > css_put(&cgrp->self); > } > > +extern struct mutex cgroup_mutex; > + > +static inline void cgroup_lock(void) > +{ > + mutex_lock(&cgroup_mutex); > +} > + > +static inline void cgroup_unlock(void) > +{ > + mutex_unlock(&cgroup_mutex); > +} > + > /** > * task_css_set_check - obtain a task's css_set with extra access conditions > * @task: the task to obtain css_set for > @@ -446,7 +458,6 @@ static inline void cgroup_put(struct cgroup *cgrp) > * as locks used during the cgroup_subsys::attach() methods. > */ > #ifdef CONFIG_PROVE_RCU > -extern struct mutex cgroup_mutex; > extern spinlock_t css_set_lock; > #define task_css_set_check(task, __c) \ > rcu_dereference_check((task)->cgroups, \ > @@ -707,6 +718,8 @@ struct cgroup; > static inline u64 cgroup_id(const struct cgroup *cgrp) { return 1; } > static inline void css_get(struct cgroup_subsys_state *css) {} > static inline void css_put(struct cgroup_subsys_state *css) {} > +static inline void cgroup_lock(void) {} > +static inline void cgroup_unlock(void) {} > static inline int cgroup_attach_task_all(struct task_struct *from, > struct task_struct *t) { return 0; } > static inline int cgroupstats_build(struct cgroupstats *stats, > diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h > index 15a04a9b5560..1c8d617e73a9 100644 > --- a/include/linux/mm_inline.h > +++ b/include/linux/mm_inline.h > @@ -106,7 +106,15 @@ static __always_inline enum lru_list folio_lru_list(struct folio *folio) > > static inline bool lru_gen_enabled(void) > { > - return true; > +#ifdef CONFIG_LRU_GEN_ENABLED > + DECLARE_STATIC_KEY_TRUE(lru_gen_caps[NR_LRU_GEN_CAPS]); > + > + return static_branch_likely(&lru_gen_caps[LRU_GEN_CORE]); > +#else > + DECLARE_STATIC_KEY_FALSE(lru_gen_caps[NR_LRU_GEN_CAPS]); > + > + return static_branch_unlikely(&lru_gen_caps[LRU_GEN_CORE]); > +#endif > } > > static inline bool lru_gen_in_fault(void) > @@ -196,7 +204,7 @@ static inline bool lru_gen_add_folio(struct lruvec *lruvec, struct folio *folio, > int zone = folio_zonenum(folio); > struct lru_gen_struct *lrugen = &lruvec->lrugen; > > - if (folio_test_unevictable(folio)) > + if (folio_test_unevictable(folio) || !lrugen->enabled) > return false; > /* > * There are three common cases for this page: > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index a2d53025a321..116c9237e401 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -371,6 +371,13 @@ enum { > LRU_GEN_FILE, > }; > > +enum { > + LRU_GEN_CORE, > + LRU_GEN_MM_WALK, > + LRU_GEN_NONLEAF_YOUNG, > + NR_LRU_GEN_CAPS > +}; > + > #define MIN_LRU_BATCH BITS_PER_LONG > #define MAX_LRU_BATCH (MIN_LRU_BATCH * 128) > > @@ -409,6 +416,8 @@ struct lru_gen_struct { > /* can be modified without holding the LRU lock */ > atomic_long_t evicted[NR_HIST_GENS][ANON_AND_FILE][MAX_NR_TIERS]; > atomic_long_t refaulted[NR_HIST_GENS][ANON_AND_FILE][MAX_NR_TIERS]; > + /* whether the multi-gen LRU is enabled */ > + bool enabled; > }; > > enum { > diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h > index 6e36e854b512..929ed3bf1a7c 100644 > --- a/kernel/cgroup/cgroup-internal.h > +++ b/kernel/cgroup/cgroup-internal.h > @@ -165,7 +165,6 @@ struct cgroup_mgctx { > #define DEFINE_CGROUP_MGCTX(name) \ > struct cgroup_mgctx name = CGROUP_MGCTX_INIT(name) > > -extern struct mutex cgroup_mutex; > extern spinlock_t css_set_lock; > extern struct cgroup_subsys *cgroup_subsys[]; > extern struct list_head cgroup_roots; > diff --git a/mm/Kconfig b/mm/Kconfig > index 804c2bca8205..050de1eae2d6 100644 > --- a/mm/Kconfig > +++ b/mm/Kconfig > @@ -901,6 +901,12 @@ config LRU_GEN > help > A high performance LRU implementation for memory overcommit. > > +config LRU_GEN_ENABLED > + bool "Enable by default" > + depends on LRU_GEN > + help > + This option enables the multi-gen LRU by default. > + > config LRU_GEN_STATS > bool "Full stats for debugging" > depends on LRU_GEN > diff --git a/mm/vmscan.c b/mm/vmscan.c > index 7375c9dae08f..55cc7d6b018b 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -3063,6 +3063,12 @@ static bool can_age_anon_pages(struct pglist_data *pgdat, > > #ifdef CONFIG_LRU_GEN > > +#ifdef CONFIG_LRU_GEN_ENABLED > +DEFINE_STATIC_KEY_ARRAY_TRUE(lru_gen_caps, NR_LRU_GEN_CAPS); > +#else > +DEFINE_STATIC_KEY_ARRAY_FALSE(lru_gen_caps, NR_LRU_GEN_CAPS); > +#endif > + > /****************************************************************************** > * shorthand helpers > ******************************************************************************/ > @@ -3099,6 +3105,15 @@ static int folio_lru_tier(struct folio *folio) > return lru_tier_from_refs(refs); > } > > +static bool get_cap(int cap) > +{ > +#ifdef CONFIG_LRU_GEN_ENABLED > + return static_branch_likely(&lru_gen_caps[cap]); > +#else > + return static_branch_unlikely(&lru_gen_caps[cap]); > +#endif > +} > + > static struct lruvec *get_lruvec(struct mem_cgroup *memcg, int nid) > { > struct pglist_data *pgdat = NODE_DATA(nid); > @@ -3892,7 +3907,8 @@ static void walk_pmd_range_locked(pud_t *pud, unsigned long next, struct vm_area > goto next; > > if (!pmd_trans_huge(pmd[i])) { > - if (IS_ENABLED(CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG)) > + if (IS_ENABLED(CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG) && > + get_cap(LRU_GEN_NONLEAF_YOUNG)) > pmdp_test_and_clear_young(vma, addr, pmd + i); > goto next; > } > @@ -3999,10 +4015,12 @@ static void walk_pmd_range(pud_t *pud, unsigned long start, unsigned long end, > priv->mm_stats[MM_PMD_TOTAL]++; > > #ifdef CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG > - if (!pmd_young(val)) > - continue; > + if (get_cap(LRU_GEN_NONLEAF_YOUNG)) { > + if (!pmd_young(val)) > + continue; > > - walk_pmd_range_locked(pud, addr, vma, walk, &pos); > + walk_pmd_range_locked(pud, addr, vma, walk, &pos); > + } > #endif > if (!priv->full_scan && !test_bloom_filter(priv->lruvec, priv->max_seq, pmd + i)) > continue; > @@ -4233,7 +4251,7 @@ static bool try_to_inc_max_seq(struct lruvec *lruvec, unsigned long max_seq, > * handful of PTEs. Spreading the work out over a period of time usually > * is less efficient, but it avoids bursty page faults. > */ > - if (!full_scan && !arch_has_hw_pte_young()) { > + if (!full_scan && (!arch_has_hw_pte_young() || !get_cap(LRU_GEN_MM_WALK))) { > success = iterate_mm_list_nowalk(lruvec, max_seq); > goto done; > } > @@ -4946,6 +4964,211 @@ static void lru_gen_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc > blk_finish_plug(&plug); > } > > +/****************************************************************************** > + * state change > + ******************************************************************************/ > + > +static bool __maybe_unused state_is_valid(struct lruvec *lruvec) > +{ > + struct lru_gen_struct *lrugen = &lruvec->lrugen; > + > + if (lrugen->enabled) { > + enum lru_list lru; > + > + for_each_evictable_lru(lru) { > + if (!list_empty(&lruvec->lists[lru])) > + return false; > + } > + } else { > + int gen, type, zone; > + > + for_each_gen_type_zone(gen, type, zone) { > + if (!list_empty(&lrugen->lists[gen][type][zone])) > + return false; > + > + /* unlikely but not a bug when reset_batch_size() is pending */ > + VM_WARN_ON(lrugen->nr_pages[gen][type][zone]); > + } > + } > + > + return true; > +} > + > +static bool fill_evictable(struct lruvec *lruvec) > +{ > + enum lru_list lru; > + int remaining = MAX_LRU_BATCH; > + > + for_each_evictable_lru(lru) { > + int type = is_file_lru(lru); > + bool active = is_active_lru(lru); > + struct list_head *head = &lruvec->lists[lru]; > + > + while (!list_empty(head)) { > + bool success; > + struct folio *folio = lru_to_folio(head); > + > + VM_BUG_ON_FOLIO(folio_test_unevictable(folio), folio); > + VM_BUG_ON_FOLIO(folio_test_active(folio) != active, folio); > + VM_BUG_ON_FOLIO(folio_is_file_lru(folio) != type, folio); > + VM_BUG_ON_FOLIO(folio_lru_gen(folio) < MAX_NR_GENS, folio); > + > + lruvec_del_folio(lruvec, folio); > + success = lru_gen_add_folio(lruvec, folio, false); > + VM_BUG_ON(!success); > + > + if (!--remaining) > + return false; > + } > + } > + > + return true; > +} > + > +static bool drain_evictable(struct lruvec *lruvec) > +{ > + int gen, type, zone; > + int remaining = MAX_LRU_BATCH; > + > + for_each_gen_type_zone(gen, type, zone) { > + struct list_head *head = &lruvec->lrugen.lists[gen][type][zone]; > + > + while (!list_empty(head)) { > + bool success; > + struct folio *folio = lru_to_folio(head); > + > + VM_BUG_ON_FOLIO(folio_test_unevictable(folio), folio); > + VM_BUG_ON_FOLIO(folio_test_active(folio), folio); > + VM_BUG_ON_FOLIO(folio_is_file_lru(folio) != type, folio); > + VM_BUG_ON_FOLIO(folio_zonenum(folio) != zone, folio); > + > + success = lru_gen_del_folio(lruvec, folio, false); > + VM_BUG_ON(!success); > + lruvec_add_folio(lruvec, folio); for example, max_seq=4(GEN=0) and max_seq-1=3, then we are supposed to put max_seq in the head of active list. but your code seems to be putting max_seq-1 after putting max_seq, then max_seq is more likely to be evicted afterwards as it is in the tail of the active list. anyway, it might not be so important. I can't imagine we will frequently switch mglru with lru dynamically. will we? > + > + if (!--remaining) > + return false; > + } > + } > + > + return true; > +} > + > +static void lru_gen_change_state(bool enable) > +{ > + static DEFINE_MUTEX(state_mutex); > + > + struct mem_cgroup *memcg; > + > + cgroup_lock(); > + cpus_read_lock(); > + get_online_mems(); > + mutex_lock(&state_mutex); > + > + if (enable == lru_gen_enabled()) > + goto unlock; > + > + if (enable) > + static_branch_enable_cpuslocked(&lru_gen_caps[LRU_GEN_CORE]); > + else > + static_branch_disable_cpuslocked(&lru_gen_caps[LRU_GEN_CORE]); > + > + memcg = mem_cgroup_iter(NULL, NULL, NULL); > + do { > + int nid; > + > + for_each_node(nid) { > + struct lruvec *lruvec = get_lruvec(memcg, nid); > + > + if (!lruvec) > + continue; > + > + spin_lock_irq(&lruvec->lru_lock); > + > + VM_BUG_ON(!seq_is_valid(lruvec)); > + VM_BUG_ON(!state_is_valid(lruvec)); > + > + lruvec->lrugen.enabled = enable; > + > + while (!(enable ? fill_evictable(lruvec) : drain_evictable(lruvec))) { > + spin_unlock_irq(&lruvec->lru_lock); > + cond_resched(); > + spin_lock_irq(&lruvec->lru_lock); > + } > + > + spin_unlock_irq(&lruvec->lru_lock); > + } > + > + cond_resched(); > + } while ((memcg = mem_cgroup_iter(NULL, memcg, NULL))); > +unlock: > + mutex_unlock(&state_mutex); > + put_online_mems(); > + cpus_read_unlock(); > + cgroup_unlock(); > +} > + > +/****************************************************************************** > + * sysfs interface > + ******************************************************************************/ > + > +static ssize_t show_enable(struct kobject *kobj, struct kobj_attribute *attr, char *buf) > +{ > + unsigned int caps = 0; > + > + if (get_cap(LRU_GEN_CORE)) > + caps |= BIT(LRU_GEN_CORE); > + > + if (arch_has_hw_pte_young() && get_cap(LRU_GEN_MM_WALK)) > + caps |= BIT(LRU_GEN_MM_WALK); > + > + if (IS_ENABLED(CONFIG_ARCH_HAS_NONLEAF_PMD_YOUNG) && get_cap(LRU_GEN_NONLEAF_YOUNG)) > + caps |= BIT(LRU_GEN_NONLEAF_YOUNG); > + > + return snprintf(buf, PAGE_SIZE, "0x%04x\n", caps); > +} > + > +static ssize_t store_enable(struct kobject *kobj, struct kobj_attribute *attr, > + const char *buf, size_t len) > +{ > + int i; > + unsigned int caps; > + > + if (tolower(*buf) == 'n') > + caps = 0; > + else if (tolower(*buf) == 'y') > + caps = -1; > + else if (kstrtouint(buf, 0, &caps)) > + return -EINVAL; > + > + for (i = 0; i < NR_LRU_GEN_CAPS; i++) { > + bool enable = caps & BIT(i); > + > + if (i == LRU_GEN_CORE) > + lru_gen_change_state(enable); > + else if (enable) > + static_branch_enable(&lru_gen_caps[i]); > + else > + static_branch_disable(&lru_gen_caps[i]); > + } > + > + return len; > +} > + > +static struct kobj_attribute lru_gen_enabled_attr = __ATTR( > + enabled, 0644, show_enable, store_enable > +); > + > +static struct attribute *lru_gen_attrs[] = { > + &lru_gen_enabled_attr.attr, > + NULL > +}; > + > +static struct attribute_group lru_gen_attr_group = { > + .name = "lru_gen", > + .attrs = lru_gen_attrs, > +}; > + > /****************************************************************************** > * initialization > ******************************************************************************/ > @@ -4956,6 +5179,7 @@ void lru_gen_init_lruvec(struct lruvec *lruvec) > struct lru_gen_struct *lrugen = &lruvec->lrugen; > > lrugen->max_seq = MIN_NR_GENS + 1; > + lrugen->enabled = lru_gen_enabled(); > > for_each_gen_type_zone(gen, type, zone) > INIT_LIST_HEAD(&lrugen->lists[gen][type][zone]); > @@ -4996,6 +5220,9 @@ static int __init init_lru_gen(void) > BUILD_BUG_ON(BIT(LRU_GEN_WIDTH) <= MAX_NR_GENS); > BUILD_BUG_ON(sizeof(MM_STAT_CODES) != NR_MM_STATS + 1); > > + if (sysfs_create_group(mm_kobj, &lru_gen_attr_group)) > + pr_err("lru_gen: failed to create sysfs group\n"); > + > return 0; > }; > late_initcall(init_lru_gen); > -- > 2.35.1.616.g0bdcbb4464-goog > Thanks Barry
