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mm: multi-gen LRU: kill switch 

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/r/20220128131006.67712-1-michel@lespinasse.org/
[3] https://lore.kernel.org/r/20220426150616.3937571-1-Liam.Howlett@oracle.com/

Link: https://lkml.kernel.org/r/20220918080010.2920238-11-yuzhao@google.com
Signed-off-by: Yu Zhao <yuzhao@google.com>
Acked-by: Brian Geffon <bgeffon@google.com>
Acked-by: Jan Alexander Steffens (heftig) <heftig@archlinux.org>
Acked-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Acked-by: Steven Barrett <steven@liquorix.net>
Acked-by: Suleiman Souhlal <suleiman@google.com>
Tested-by: Daniel Byrne <djbyrne@mtu.edu>
Tested-by: Donald Carr <d@chaos-reins.com>
Tested-by: Holger Hoffstätte <holger@applied-asynchrony.com>
Tested-by: Konstantin Kharlamov <Hi-Angel@yandex.ru>
Tested-by: Shuang Zhai <szhai2@cs.rochester.edu>
Tested-by: Sofia Trinh <sofia.trinh@edi.works>
Tested-by: Vaibhav Jain <vaibhav@linux.ibm.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Hillf Danton <hdanton@sina.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Michael Larabel <Michael@MichaelLarabel.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Yu Zhao 2022-09-18 02:00:07 -06:00 committed by Andrew Morton
parent f76c833788
commit 354ed59744
6 changed files with 265 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

15
include/linux/cgroup.h
View File

@ -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, \
@ -708,6 +719,8 @@ 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,

15
include/linux/mm_inline.h
View File

@ -106,10 +106,21 @@ static __always_inline enum lru_list folio_lru_list(struct folio *folio)
#ifdef CONFIG_LRU_GEN
#ifdef CONFIG_LRU_GEN_ENABLED
static inline bool lru_gen_enabled(void)
{
return true;
DECLARE_STATIC_KEY_TRUE(lru_gen_caps[NR_LRU_GEN_CAPS]);
return static_branch_likely(&lru_gen_caps[LRU_GEN_CORE]);
}
#else
static inline bool lru_gen_enabled(void)
{
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)
{
@ -222,7 +233,7 @@ static inline bool lru_gen_add_folio(struct lruvec *lruvec, struct folio *folio,
VM_WARN_ON_ONCE_FOLIO(gen != -1, folio);
if (folio_test_unevictable(folio))
if (folio_test_unevictable(folio) || !lrugen->enabled)
return false;
/*
* There are three common cases for this page:

9
include/linux/mmzone.h
View File

@ -387,6 +387,13 @@ 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 * 64)
@ -428,6 +435,8 @@ 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 {

1
kernel/cgroup/cgroup-internal.h
View File

@ -164,7 +164,6 @@ 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;

6
mm/Kconfig
View File

@ -1127,6 +1127,12 @@ config LRU_GEN
help
A high performance LRU implementation to overcommit memory.
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

228
mm/vmscan.c
View File

@ -51,6 +51,7 @@
#include <linux/psi.h>
#include <linux/pagewalk.h>
#include <linux/shmem_fs.h>
#include <linux/ctype.h>
#include <asm/tlbflush.h>
#include <asm/div64.h>
@ -3070,6 +3071,14 @@ 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);
#define get_cap(cap) static_branch_likely(&lru_gen_caps[cap])
#else
DEFINE_STATIC_KEY_ARRAY_FALSE(lru_gen_caps, NR_LRU_GEN_CAPS);
#define get_cap(cap) static_branch_unlikely(&lru_gen_caps[cap])
#endif
/******************************************************************************
* shorthand helpers
******************************************************************************/
@ -3946,7 +3955,8 @@ 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;
}
@ -4044,10 +4054,12 @@ restart:
walk->mm_stats[MM_NONLEAF_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, args, bitmap, &pos);
walk_pmd_range_locked(pud, addr, vma, args, bitmap, &pos);
}
#endif
if (!walk->force_scan && !test_bloom_filter(walk->lruvec, walk->max_seq, pmd + i))
continue;
@ -4309,7 +4321,7 @@ 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 (!arch_has_hw_pte_young()) {
if (!(arch_has_hw_pte_young() && get_cap(LRU_GEN_MM_WALK))) {
success = iterate_mm_list_nowalk(lruvec, max_seq);
goto done;
}
@ -5074,6 +5086,208 @@ done:
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;
}
}
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_WARN_ON_ONCE_FOLIO(folio_test_unevictable(folio), folio);
VM_WARN_ON_ONCE_FOLIO(folio_test_active(folio) != active, folio);
VM_WARN_ON_ONCE_FOLIO(folio_is_file_lru(folio) != type, folio);
VM_WARN_ON_ONCE_FOLIO(folio_lru_gen(folio) != -1, folio);
lruvec_del_folio(lruvec, folio);
success = lru_gen_add_folio(lruvec, folio, false);
VM_WARN_ON_ONCE(!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_WARN_ON_ONCE_FOLIO(folio_test_unevictable(folio), folio);
VM_WARN_ON_ONCE_FOLIO(folio_test_active(folio), folio);
VM_WARN_ON_ONCE_FOLIO(folio_is_file_lru(folio) != type, folio);
VM_WARN_ON_ONCE_FOLIO(folio_zonenum(folio) != zone, folio);
success = lru_gen_del_folio(lruvec, folio, false);
VM_WARN_ON_ONCE(!success);
lruvec_add_folio(lruvec, folio);
if (!--remaining)
return false;
}
}
return true;
}
static void lru_gen_change_state(bool enabled)
{
static DEFINE_MUTEX(state_mutex);
struct mem_cgroup *memcg;
cgroup_lock();
cpus_read_lock();
get_online_mems();
mutex_lock(&state_mutex);
if (enabled == lru_gen_enabled())
goto unlock;
if (enabled)
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_WARN_ON_ONCE(!seq_is_valid(lruvec));
VM_WARN_ON_ONCE(!state_is_valid(lruvec));
lruvec->lrugen.enabled = enabled;
while (!(enabled ? 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_enabled(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_enabled(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 enabled = caps & BIT(i);
if (i == LRU_GEN_CORE)
lru_gen_change_state(enabled);
else if (enabled)
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_enabled, store_enabled
);
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
******************************************************************************/
@ -5084,6 +5298,7 @@ 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]);
@ -5123,6 +5338,9 @@ static int __init init_lru_gen(void)
BUILD_BUG_ON(MIN_NR_GENS + 1 >= MAX_NR_GENS);
BUILD_BUG_ON(BIT(LRU_GEN_WIDTH) <= MAX_NR_GENS);
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);