[PATCH v3 00/14] Multigenerational LRU Framework

[PATCH v3 00/14] Multigenerational LRU Framework

[Yu Zhao]

What's new in v3
================
1) Fixed a bug reported by the Arch Linux kernel team:
   https://github.com/zen-kernel/zen-kernel/issues/207
2) Rebased to v5.13-rc2.

Highlights from v2
==================
Konstantin Kharlamov <hi-angel@yandex.ru> reported:
  My success story: I have Archlinux with 8G RAM + zswap + swap. While
  developing, I have lots of apps opened such as multiple LSP-servers
  for different langs, chats, two browsers, etc. Usually, my system
  gets quickly to a point of SWAP-storms, where I have to kill
  LSP-servers, restart browsers to free memory, etc, otherwise the
  system lags heavily and is barely usable.
 
  1.5 day ago I migrated from 5.11.15 kernel to 5.12 + the LRU
  patchset, and I started up by opening lots of apps to create memory
  pressure, and worked for a day like this. Till now I had *not a
  single SWAP-storm*, and mind you I got 3.4G in SWAP. I was never
  getting to the point of 3G in SWAP before without a single
  SWAP-storm.

TLDR
====
The current page reclaim is too expensive in terms of CPU usage and
often making poor choices about what to evict. We would like to offer
an alternative framework that is performant, versatile and
straightforward.

Repo
====
git fetch https://linux-mm.googlesource.com/page-reclaim refs/changes/53/1253/1

Problems
========
Notion of active/inactive
-------------------------
Data centers need to predict whether a job can successfully land on a
machine without actually impacting the existing jobs. The granularity
of the active/inactive is too coarse to be useful for job schedulers
to make such decisions. In addition, data centers need to monitor
their memory utilization for horizontal scaling. The active/inactive
cannot give any insight into a pool of machines because aggregating
them across multiple machines without a common frame of reference
yields no meaningful results.

Phones and laptops need to make good choices about what to evict,
since they are more sensitive to the major faults and the power
consumption. Major faults can cause "janks" (slow UI renderings) and
negatively impact user experience. The selection between anon and file
types has been suboptimal because direct comparisons between them are
infeasible based on the notion of active/inactive. On phones and
laptops, executable pages are frequently evicted despite the fact that
there are many less recently used anon pages. Conversely, on
workstations building large projects, anon pages are occasionally
swapped out while page cache contains many less recently used pages.

Fundamentally, the notion of active/inactive has very limited ability
to measure temporal locality.

Incremental scans via rmap
--------------------------
Each incremental scan picks up at where the last scan left off and
stops after it has found a handful of unreferenced pages. For
workloads using a large amount of anon memory, incremental scans lose
the advantage under sustained memory pressure due to high ratios of
the number of scanned pages to the number of reclaimed pages. On top
of this, the rmap has complex data structures. And the combined
effects typically result in a high amount of CPU usage in the reclaim
path.

Simply put, incremental scans via rmap have no regard for spatial
locality.

Solutions
=========
Notion of generation numbers
----------------------------
The notion of generation numbers introduces a temporal dimension. Each
generation is a dot on the timeline and it includes all pages that
have been referenced since it was created.

Given an lruvec, scans of anon and file types and selections between
them are all based on direct comparisons of generation numbers, which
are simple and yet effective.

A larger number of pages can be spread out across a configurable
number of generations, which are associated with timestamps and
therefore aggregatable. This is specifically designed for data centers
that require working set estimation and proactive reclaim.

Differential scans via page tables
----------------------------------
Each differential scan discovers all pages that have been referenced
since the last scan. It walks the mm_struct list associated with an
lruvec to scan page tables of processes that have been scheduled since
the last scan. The cost of each differential scan is roughly
proportional to the number of referenced pages it discovers. Page
tables usually have good memory locality. The end result is generally
a significant reduction in CPU usage, for workloads using a large
amount of anon memory.

For workloads that have extremely sparse page tables, it is still
possible to fall back to incremental scans via rmap.

Framework
=========
For each lruvec, evictable pages are divided into multiple
generations. The youngest generation number is stored in
lrugen->max_seq for both anon and file types as they are aged on an
equal footing. The oldest generation numbers are stored in
lrugen->min_seq[2] separately for anon and file types as clean file
pages can be evicted regardless of may_swap or may_writepage. These
three variables are monotonically increasing. Generation numbers are
truncated into order_base_2(MAX_NR_GENS+1) bits in order to fit into
page->flags. The sliding window technique is used to prevent truncated
generation numbers from overlapping. Each truncated generation number
is an index to
lrugen->lists[MAX_NR_GENS][ANON_AND_FILE][MAX_NR_ZONES]. Evictable
pages are added to the per-zone lists indexed by lrugen->max_seq or
lrugen->min_seq[2] (modulo MAX_NR_GENS), depending on their types.

Each generation is then divided into multiple tiers. Tiers represent
levels of usage from file descriptors only. Pages accessed N times via
file descriptors belong to tier order_base_2(N). Each generation
contains at most MAX_NR_TIERS tiers, and they require additional
MAX_NR_TIERS-2 bits in page->flags. In contrast to moving across
generations which requires the lru lock for the list operations,
moving across tiers only involves an atomic operation on page->flags
and therefore has a negligible cost. A feedback loop modeled after the
PID controller monitors the refault rates across all tiers and decides
when to activate pages from which tiers in the reclaim path.

The framework comprises two conceptually independent components: the
aging and the eviction, which can be invoked separately from user
space for the purpose of working set estimation and proactive reclaim.

Aging
-----
The aging produces young generations. Given an lruvec, the aging scans
page tables for referenced pages of this lruvec. Upon finding one, the
aging updates its generation number to max_seq. After each round of
scan, the aging increments max_seq.

The aging maintains either a system-wide mm_struct list or per-memcg
mm_struct lists, and it only scans page tables of processes that have
been scheduled since the last scan.

The aging is due when both of min_seq[2] reaches max_seq-1, assuming
both anon and file types are reclaimable.

Eviction
--------
The eviction consumes old generations. Given an lruvec, the eviction
scans the pages on the per-zone lists indexed by either of min_seq[2].
It first tries to select a type based on the values of min_seq[2].
When anon and file types are both available from the same generation,
it selects the one that has a lower refault rate.

During a scan, the eviction sorts pages according to their new
generation numbers, if the aging has found them referenced. It also
moves pages from the tiers that have higher refault rates than tier 0
to the next generation.

When it finds all the per-zone lists of a selected type are empty, the
eviction increments min_seq[2] indexed by this selected type.

Use cases
=========
High anon workloads
-------------------
Our real-world benchmark that browses popular websites in multiple
Chrome tabs demonstrates 51% less CPU usage from kswapd and 52% (full)
less PSI.

Without this patchset, the profile of kswapd looks like:
  31.03%  page_vma_mapped_walk
  25.59%  lzo1x_1_do_compress
   4.63%  do_raw_spin_lock
   3.89%  vma_interval_tree_iter_next
   3.33%  vma_interval_tree_subtree_search

With this patchset, it looks like:
  49.36%  lzo1x_1_do_compress
   4.54%  page_vma_mapped_walk
   4.45%  memset_erms
   3.47%  walk_pte_range
   2.88%  zram_bvec_rw

In addition, direct reclaim latency is reduced by 22% at 99th
percentile and the number of refaults is reduced by 7%. Both metrics
are important to phones and laptops as they are highly correlated to
user experience.

High page cache workloads
-------------------------
Tiers are specifically designed to improve the performance of page
cache under memory pressure. The fio/io_uring benchmark shows 14%
increase in IOPS when randomly accessing in buffered I/O mode.

Without this patchset, the profile of fio/io_uring looks like:
  Children  Self   Symbol
  -----------------------------------
  12.03%    0.03%  __page_cache_alloc
   6.53%    0.83%  shrink_active_list
   2.53%    0.44%  mark_page_accessed

With this patchset, it looks like:
  Children  Self   Symbol
  -----------------------------------
  9.45%     0.03%  __page_cache_alloc
  0.52%     0.46%  mark_page_accessed

Working set estimation
----------------------
User space can invoke the aging by writing "+ memcg_id node_id gen
[swappiness]" to /sys/kernel/debug/lru_gen. This debugfs interface
also provides the birth time and the size of each generation.

For example, given a pool of machines, a job scheduler periodically
invokes the aging to estimate the working set of each machine. And it
ranks the machines based on the sizes of their working sets and
selects the most ideal ones to land new jobs.

Proactive reclaim
-----------------
User space can invoke the eviction by writing "- memcg_id node_id gen
[swappiness] [nr_to_reclaim]" to /sys/kernel/debug/lru_gen. Multiple
command lines are supported, so does concatenation with delimiters.

For example, a job scheduler can invoke the eviction if it anticipates
new jobs. The savings from proactive reclaim may provide certain SLA
when new jobs actually land.

Yu Zhao (14):
  include/linux/memcontrol.h: do not warn in page_memcg_rcu() if
    !CONFIG_MEMCG
  include/linux/nodemask.h: define next_memory_node() if !CONFIG_NUMA
  include/linux/cgroup.h: export cgroup_mutex
  mm, x86: support the access bit on non-leaf PMD entries
  mm/vmscan.c: refactor shrink_node()
  mm/workingset.c: refactor pack_shadow() and unpack_shadow()
  mm: multigenerational lru: groundwork
  mm: multigenerational lru: activation
  mm: multigenerational lru: mm_struct list
  mm: multigenerational lru: aging
  mm: multigenerational lru: eviction
  mm: multigenerational lru: user interface
  mm: multigenerational lru: Kconfig
  mm: multigenerational lru: documentation

 Documentation/vm/index.rst        |    1 +
 Documentation/vm/multigen_lru.rst |  143 ++
 arch/Kconfig                      |    9 +
 arch/x86/Kconfig                  |    1 +
 arch/x86/include/asm/pgtable.h    |    2 +-
 arch/x86/mm/pgtable.c             |    5 +-
 fs/exec.c                         |    2 +
 fs/fuse/dev.c                     |    3 +-
 include/linux/cgroup.h            |   15 +-
 include/linux/memcontrol.h        |    7 +-
 include/linux/mm.h                |    2 +
 include/linux/mm_inline.h         |  234 +++
 include/linux/mm_types.h          |  107 ++
 include/linux/mmzone.h            |  117 ++
 include/linux/nodemask.h          |    1 +
 include/linux/page-flags-layout.h |   19 +-
 include/linux/page-flags.h        |    4 +-
 include/linux/pgtable.h           |    4 +-
 include/linux/swap.h              |    4 +-
 kernel/bounds.c                   |    6 +
 kernel/events/uprobes.c           |    2 +-
 kernel/exit.c                     |    1 +
 kernel/fork.c                     |   10 +
 kernel/kthread.c                  |    1 +
 kernel/sched/core.c               |    2 +
 mm/Kconfig                        |   58 +
 mm/huge_memory.c                  |    5 +-
 mm/khugepaged.c                   |    2 +-
 mm/memcontrol.c                   |   28 +
 mm/memory.c                       |   10 +-
 mm/migrate.c                      |    2 +-
 mm/mm_init.c                      |    6 +-
 mm/mmzone.c                       |    2 +
 mm/rmap.c                         |    6 +
 mm/swap.c                         |   22 +-
 mm/swapfile.c                     |    6 +-
 mm/userfaultfd.c                  |    2 +-
 mm/vmscan.c                       | 2638 ++++++++++++++++++++++++++++-
 mm/workingset.c                   |  169 +-
 39 files changed, 3498 insertions(+), 160 deletions(-)
 create mode 100644 Documentation/vm/multigen_lru.rst

-- 
2.31.1.751.gd2f1c929bd-goog

[PATCH v3 01/14] include/linux/memcontrol.h: do not warn in page_memcg_rcu() if !CONFIG_MEMCG

[Yu Zhao]

page_memcg_rcu() warns on !rcu_read_lock_held() regardless of
CONFIG_MEMCG. The following legit code trips the warning when
!CONFIG_MEMCG, since lock_page_memcg() and unlock_page_memcg() are
empty for this config.

  memcg = lock_page_memcg(page1)
    (rcu_read_lock() if CONFIG_MEMCG=y)

  do something to page1

  if (page_memcg_rcu(page2) == memcg)
    do something to page2 too as it cannot be migrated away from the
    memcg either.

  unlock_page_memcg(page1)
    (rcu_read_unlock() if CONFIG_MEMCG=y)

Locking/unlocking rcu consistently for both configs is rigorous but it
also forces unnecessary locking upon users who have no interest in
CONFIG_MEMCG.

This patch removes the assertion for !CONFIG_MEMCG, because
page_memcg_rcu() has a few callers and there are no concerns regarding
their correctness at the moment.

Signed-off-by: Yu Zhao <yuzhao@google.com>
Tested-by: Konstantin Kharlamov <Hi-Angel@yandex.ru>
---
 include/linux/memcontrol.h | 1 -
 1 file changed, 1 deletion(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index c193be760709..6bcac3d91dd1 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -1131,7 +1131,6 @@ static inline struct mem_cgroup *page_memcg(struct page *page)
 
 static inline struct mem_cgroup *page_memcg_rcu(struct page *page)
 {
-	WARN_ON_ONCE(!rcu_read_lock_held());
 	return NULL;
 }
 
-- 
2.31.1.751.gd2f1c929bd-goog

[PATCH v3 02/14] include/linux/nodemask.h: define next_memory_node() if !CONFIG_NUMA

[Yu Zhao]

Currently next_memory_node only exists when CONFIG_NUMA=y. This patch
adds the macro for !CONFIG_NUMA.

Signed-off-by: Yu Zhao <yuzhao@google.com>
Tested-by: Konstantin Kharlamov <Hi-Angel@yandex.ru>
---
 include/linux/nodemask.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/include/linux/nodemask.h b/include/linux/nodemask.h
index ac398e143c9a..89fe4e3592f9 100644
--- a/include/linux/nodemask.h
+++ b/include/linux/nodemask.h
@@ -486,6 +486,7 @@ static inline int num_node_state(enum node_states state)
 #define first_online_node	0
 #define first_memory_node	0
 #define next_online_node(nid)	(MAX_NUMNODES)
+#define next_memory_node(nid)	(MAX_NUMNODES)
 #define nr_node_ids		1U
 #define nr_online_nodes		1U
 
-- 
2.31.1.751.gd2f1c929bd-goog

[PATCH v3 03/14] include/linux/cgroup.h: export cgroup_mutex

[Yu Zhao]

cgroup_mutex is needed to synchronize with memcg creations.

Signed-off-by: Yu Zhao <yuzhao@google.com>
Tested-by: Konstantin Kharlamov <Hi-Angel@yandex.ru>
---
 include/linux/cgroup.h | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 4f2f79de083e..bd5744360cfa 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,				\
@@ -704,6 +715,8 @@ 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,
-- 
2.31.1.751.gd2f1c929bd-goog

[PATCH v3 04/14] mm, x86: support the access bit on non-leaf PMD entries

[Yu Zhao]

Some architectures support the accessed bit on non-leaf PMD entries
(parents) in addition to leaf PTE entries (children) where pages are
mapped, e.g., x86_64 sets the accessed bit on a parent when using it
as part of linear-address translation [1]. Page table walkers who are
interested in the accessed bit on children can take advantage of this:
they do not need to search the children when the accessed bit is not
set on a parent, given that they have previously cleared the accessed
bit on this parent.

[1]: Intel 64 and IA-32 Architectures Software Developer's Manual
     Volume 3 (October 2019), section 4.8

Signed-off-by: Yu Zhao <yuzhao@google.com>
Tested-by: Konstantin Kharlamov <Hi-Angel@yandex.ru>
---
 arch/Kconfig                   | 9 +++++++++
 arch/x86/Kconfig               | 1 +
 arch/x86/include/asm/pgtable.h | 2 +-
 arch/x86/mm/pgtable.c          | 5 ++++-
 include/linux/pgtable.h        | 4 ++--
 5 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index c45b770d3579..e3812adc69f7 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -826,6 +826,15 @@ config HAVE_ARCH_TRANSPARENT_HUGEPAGE
 config HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
 	bool
 
+config HAVE_ARCH_PARENT_PMD_YOUNG
+	bool
+	depends on PGTABLE_LEVELS > 2
+	help
+	  Architectures that select this are able to set the accessed bit on
+	  non-leaf PMD entries in addition to leaf PTE entries where pages are
+	  mapped. For them, page table walkers that clear the accessed bit may
+	  stop at non-leaf PMD entries if they do not see the accessed bit.
+
 config HAVE_ARCH_HUGE_VMAP
 	bool
 
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 0045e1b44190..f619055c4537 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -170,6 +170,7 @@ config X86
 	select HAVE_ARCH_TRACEHOOK
 	select HAVE_ARCH_TRANSPARENT_HUGEPAGE
 	select HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD if X86_64
+	select HAVE_ARCH_PARENT_PMD_YOUNG	if X86_64
 	select HAVE_ARCH_USERFAULTFD_WP         if X86_64 && USERFAULTFD
 	select HAVE_ARCH_USERFAULTFD_MINOR	if X86_64 && USERFAULTFD
 	select HAVE_ARCH_VMAP_STACK		if X86_64
diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index b1099f2d9800..3a24d2af4e9b 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -846,7 +846,7 @@ static inline unsigned long pmd_page_vaddr(pmd_t pmd)
 
 static inline int pmd_bad(pmd_t pmd)
 {
-	return (pmd_flags(pmd) & ~_PAGE_USER) != _KERNPG_TABLE;
+	return ((pmd_flags(pmd) | _PAGE_ACCESSED) & ~_PAGE_USER) != _KERNPG_TABLE;
 }
 
 static inline unsigned long pages_to_mb(unsigned long npg)
diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index d27cf69e811d..b968d6bd28b6 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -550,7 +550,7 @@ int ptep_test_and_clear_young(struct vm_area_struct *vma,
 	return ret;
 }
 
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HAVE_ARCH_PARENT_PMD_YOUNG)
 int pmdp_test_and_clear_young(struct vm_area_struct *vma,
 			      unsigned long addr, pmd_t *pmdp)
 {
@@ -562,6 +562,9 @@ int pmdp_test_and_clear_young(struct vm_area_struct *vma,
 
 	return ret;
 }
+#endif
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
 int pudp_test_and_clear_young(struct vm_area_struct *vma,
 			      unsigned long addr, pud_t *pudp)
 {
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 46b13780c2c8..94ecc1d277a2 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -193,7 +193,7 @@ static inline int ptep_test_and_clear_young(struct vm_area_struct *vma,
 #endif
 
 #ifndef __HAVE_ARCH_PMDP_TEST_AND_CLEAR_YOUNG
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HAVE_ARCH_PARENT_PMD_YOUNG)
 static inline int pmdp_test_and_clear_young(struct vm_area_struct *vma,
 					    unsigned long address,
 					    pmd_t *pmdp)
@@ -214,7 +214,7 @@ static inline int pmdp_test_and_clear_young(struct vm_area_struct *vma,
 	BUILD_BUG();
 	return 0;
 }
-#endif /* CONFIG_TRANSPARENT_HUGEPAGE */
+#endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HAVE_ARCH_PARENT_PMD_YOUNG */
 #endif
 
 #ifndef __HAVE_ARCH_PTEP_CLEAR_YOUNG_FLUSH
-- 
2.31.1.751.gd2f1c929bd-goog

[PATCH v3 05/14] mm/vmscan.c: refactor shrink_node()

[Yu Zhao]

Heuristics that determine scan balance between anon and file LRUs are
rather independent. Move them into a separate function to improve
readability.

Signed-off-by: Yu Zhao <yuzhao@google.com>
Tested-by: Konstantin Kharlamov <Hi-Angel@yandex.ru>
---
 mm/vmscan.c | 186 +++++++++++++++++++++++++++-------------------------
 1 file changed, 98 insertions(+), 88 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 5199b9696bab..2339459c97d4 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2421,6 +2421,103 @@ enum scan_balance {
 	SCAN_FILE,
 };
 
+static void prepare_scan_count(pg_data_t *pgdat, struct scan_control *sc)
+{
+	unsigned long file;
+	struct lruvec *target_lruvec;
+
+	target_lruvec = mem_cgroup_lruvec(sc->target_mem_cgroup, pgdat);
+
+	/*
+	 * Determine the scan balance between anon and file LRUs.
+	 */
+	spin_lock_irq(&target_lruvec->lru_lock);
+	sc->anon_cost = target_lruvec->anon_cost;
+	sc->file_cost = target_lruvec->file_cost;
+	spin_unlock_irq(&target_lruvec->lru_lock);
+
+	/*
+	 * Target desirable inactive:active list ratios for the anon
+	 * and file LRU lists.
+	 */
+	if (!sc->force_deactivate) {
+		unsigned long refaults;
+
+		refaults = lruvec_page_state(target_lruvec,
+				WORKINGSET_ACTIVATE_ANON);
+		if (refaults != target_lruvec->refaults[0] ||
+			inactive_is_low(target_lruvec, LRU_INACTIVE_ANON))
+			sc->may_deactivate |= DEACTIVATE_ANON;
+		else
+			sc->may_deactivate &= ~DEACTIVATE_ANON;
+
+		/*
+		 * When refaults are being observed, it means a new
+		 * workingset is being established. Deactivate to get
+		 * rid of any stale active pages quickly.
+		 */
+		refaults = lruvec_page_state(target_lruvec,
+				WORKINGSET_ACTIVATE_FILE);
+		if (refaults != target_lruvec->refaults[1] ||
+		    inactive_is_low(target_lruvec, LRU_INACTIVE_FILE))
+			sc->may_deactivate |= DEACTIVATE_FILE;
+		else
+			sc->may_deactivate &= ~DEACTIVATE_FILE;
+	} else
+		sc->may_deactivate = DEACTIVATE_ANON | DEACTIVATE_FILE;
+
+	/*
+	 * If we have plenty of inactive file pages that aren't
+	 * thrashing, try to reclaim those first before touching
+	 * anonymous pages.
+	 */
+	file = lruvec_page_state(target_lruvec, NR_INACTIVE_FILE);
+	if (file >> sc->priority && !(sc->may_deactivate & DEACTIVATE_FILE))
+		sc->cache_trim_mode = 1;
+	else
+		sc->cache_trim_mode = 0;
+
+	/*
+	 * Prevent the reclaimer from falling into the cache trap: as
+	 * cache pages start out inactive, every cache fault will tip
+	 * the scan balance towards the file LRU.  And as the file LRU
+	 * shrinks, so does the window for rotation from references.
+	 * This means we have a runaway feedback loop where a tiny
+	 * thrashing file LRU becomes infinitely more attractive than
+	 * anon pages.  Try to detect this based on file LRU size.
+	 */
+	if (!cgroup_reclaim(sc)) {
+		unsigned long total_high_wmark = 0;
+		unsigned long free, anon;
+		int z;
+
+		free = sum_zone_node_page_state(pgdat->node_id, NR_FREE_PAGES);
+		file = node_page_state(pgdat, NR_ACTIVE_FILE) +
+			   node_page_state(pgdat, NR_INACTIVE_FILE);
+
+		for (z = 0; z < MAX_NR_ZONES; z++) {
+			struct zone *zone = &pgdat->node_zones[z];
+
+			if (!managed_zone(zone))
+				continue;
+
+			total_high_wmark += high_wmark_pages(zone);
+		}
+
+		/*
+		 * Consider anon: if that's low too, this isn't a
+		 * runaway file reclaim problem, but rather just
+		 * extreme pressure. Reclaim as per usual then.
+		 */
+		anon = node_page_state(pgdat, NR_INACTIVE_ANON);
+
+		sc->file_is_tiny =
+			file + free <= total_high_wmark &&
+			!(sc->may_deactivate & DEACTIVATE_ANON) &&
+			anon >> sc->priority;
+	}
+}
+
 /*
  * Determine how aggressively the anon and file LRU lists should be
  * scanned.  The relative value of each set of LRU lists is determined
@@ -2866,7 +2963,6 @@ static void shrink_node(pg_data_t *pgdat, struct scan_control *sc)
 	unsigned long nr_reclaimed, nr_scanned;
 	struct lruvec *target_lruvec;
 	bool reclaimable = false;
-	unsigned long file;
 
 	target_lruvec = mem_cgroup_lruvec(sc->target_mem_cgroup, pgdat);
 
@@ -2876,93 +2972,7 @@ static void shrink_node(pg_data_t *pgdat, struct scan_control *sc)
 	nr_reclaimed = sc->nr_reclaimed;
 	nr_scanned = sc->nr_scanned;
 
-	/*
-	 * Determine the scan balance between anon and file LRUs.
-	 */
-	spin_lock_irq(&target_lruvec->lru_lock);
-	sc->anon_cost = target_lruvec->anon_cost;
-	sc->file_cost = target_lruvec->file_cost;
-	spin_unlock_irq(&target_lruvec->lru_lock);
-
-	/*
-	 * Target desirable inactive:active list ratios for the anon
-	 * and file LRU lists.
-	 */
-	if (!sc->force_deactivate) {
-		unsigned long refaults;
-
-		refaults = lruvec_page_state(target_lruvec,
-				WORKINGSET_ACTIVATE_ANON);
-		if (refaults != target_lruvec->refaults[0] ||
-			inactive_is_low(target_lruvec, LRU_INACTIVE_ANON))
-			sc->may_deactivate |= DEACTIVATE_ANON;
-		else
-			sc->may_deactivate &= ~DEACTIVATE_ANON;
-
-		/*
-		 * When refaults are being observed, it means a new
-		 * workingset is being established. Deactivate to get
-		 * rid of any stale active pages quickly.
-		 */
-		refaults = lruvec_page_state(target_lruvec,
-				WORKINGSET_ACTIVATE_FILE);
-		if (refaults != target_lruvec->refaults[1] ||
-		    inactive_is_low(target_lruvec, LRU_INACTIVE_FILE))
-			sc->may_deactivate |= DEACTIVATE_FILE;
-		else
-			sc->may_deactivate &= ~DEACTIVATE_FILE;
-	} else
-		sc->may_deactivate = DEACTIVATE_ANON | DEACTIVATE_FILE;
-
-	/*
-	 * If we have plenty of inactive file pages that aren't
-	 * thrashing, try to reclaim those first before touching
-	 * anonymous pages.
-	 */
-	file = lruvec_page_state(target_lruvec, NR_INACTIVE_FILE);
-	if (file >> sc->priority && !(sc->may_deactivate & DEACTIVATE_FILE))
-		sc->cache_trim_mode = 1;
-	else
-		sc->cache_trim_mode = 0;
-
-	/*
-	 * Prevent the reclaimer from falling into the cache trap: as
-	 * cache pages start out inactive, every cache fault will tip
-	 * the scan balance towards the file LRU.  And as the file LRU
-	 * shrinks, so does the window for rotation from references.
-	 * This means we have a runaway feedback loop where a tiny
-	 * thrashing file LRU becomes infinitely more attractive than
-	 * anon pages.  Try to detect this based on file LRU size.
-	 */
-	if (!cgroup_reclaim(sc)) {
-		unsigned long total_high_wmark = 0;
-		unsigned long free, anon;
-		int z;
-
-		free = sum_zone_node_page_state(pgdat->node_id, NR_FREE_PAGES);
-		file = node_page_state(pgdat, NR_ACTIVE_FILE) +
-			   node_page_state(pgdat, NR_INACTIVE_FILE);
-
-		for (z = 0; z < MAX_NR_ZONES; z++) {
-			struct zone *zone = &pgdat->node_zones[z];
-			if (!managed_zone(zone))
-				continue;
-
-			total_high_wmark += high_wmark_pages(zone);
-		}
-
-		/*
-		 * Consider anon: if that's low too, this isn't a
-		 * runaway file reclaim problem, but rather just
-		 * extreme pressure. Reclaim as per usual then.
-		 */
-		anon = node_page_state(pgdat, NR_INACTIVE_ANON);
-
-		sc->file_is_tiny =
-			file + free <= total_high_wmark &&
-			!(sc->may_deactivate & DEACTIVATE_ANON) &&
-			anon >> sc->priority;
-	}
+	prepare_scan_count(pgdat, sc);
 
 	shrink_node_memcgs(pgdat, sc);
 
-- 
2.31.1.751.gd2f1c929bd-goog

[PATCH v3 06/14] mm/workingset.c: refactor pack_shadow() and unpack_shadow()

[Yu Zhao]

This patches moves the bucket order and PageWorkingset() out of
pack_shadow() and unpack_shadow(). It has no merits on its own but
makes the upcoming changes to mm/workingset.c less diffy.

Signed-off-by: Yu Zhao <yuzhao@google.com>
Tested-by: Konstantin Kharlamov <Hi-Angel@yandex.ru>
---
 mm/workingset.c | 53 ++++++++++++++++++++-----------------------------
 1 file changed, 22 insertions(+), 31 deletions(-)

diff --git a/mm/workingset.c b/mm/workingset.c
index b7cdeca5a76d..edb8aed2587e 100644
--- a/mm/workingset.c
+++ b/mm/workingset.c
@@ -168,9 +168,9 @@
  * refault distance will immediately activate the refaulting page.
  */
 
-#define EVICTION_SHIFT	((BITS_PER_LONG - BITS_PER_XA_VALUE) +	\
-			 1 + NODES_SHIFT + MEM_CGROUP_ID_SHIFT)
-#define EVICTION_MASK	(~0UL >> EVICTION_SHIFT)
+#define EVICTION_SHIFT		(BITS_PER_XA_VALUE - MEM_CGROUP_ID_SHIFT - NODES_SHIFT)
+#define EVICTION_MASK		(BIT(EVICTION_SHIFT) - 1)
+#define WORKINGSET_WIDTH	1
 
 /*
  * Eviction timestamps need to be able to cover the full range of
@@ -182,36 +182,23 @@
  */
 static unsigned int bucket_order __read_mostly;
 
-static void *pack_shadow(int memcgid, pg_data_t *pgdat, unsigned long eviction,
-			 bool workingset)
+static void *pack_shadow(int memcg_id, struct pglist_data *pgdat, unsigned long val)
 {
-	eviction >>= bucket_order;
-	eviction &= EVICTION_MASK;
-	eviction = (eviction << MEM_CGROUP_ID_SHIFT) | memcgid;
-	eviction = (eviction << NODES_SHIFT) | pgdat->node_id;
-	eviction = (eviction << 1) | workingset;
+	val = (val << MEM_CGROUP_ID_SHIFT) | memcg_id;
+	val = (val << NODES_SHIFT) | pgdat->node_id;
 
-	return xa_mk_value(eviction);
+	return xa_mk_value(val);
 }
 
-static void unpack_shadow(void *shadow, int *memcgidp, pg_data_t **pgdat,
-			  unsigned long *evictionp, bool *workingsetp)
+static unsigned long unpack_shadow(void *shadow, int *memcg_id, struct pglist_data **pgdat)
 {
-	unsigned long entry = xa_to_value(shadow);
-	int memcgid, nid;
-	bool workingset;
+	unsigned long val = xa_to_value(shadow);
 
-	workingset = entry & 1;
-	entry >>= 1;
-	nid = entry & ((1UL << NODES_SHIFT) - 1);
-	entry >>= NODES_SHIFT;
-	memcgid = entry & ((1UL << MEM_CGROUP_ID_SHIFT) - 1);
-	entry >>= MEM_CGROUP_ID_SHIFT;
+	*pgdat = NODE_DATA(val & (BIT(NODES_SHIFT) - 1));
+	val >>= NODES_SHIFT;
+	*memcg_id = val & (BIT(MEM_CGROUP_ID_SHIFT) - 1);
 
-	*memcgidp = memcgid;
-	*pgdat = NODE_DATA(nid);
-	*evictionp = entry << bucket_order;
-	*workingsetp = workingset;
+	return val >> MEM_CGROUP_ID_SHIFT;
 }
 
 /**
@@ -266,8 +253,10 @@ void *workingset_eviction(struct page *page, struct mem_cgroup *target_memcg)
 	/* XXX: target_memcg can be NULL, go through lruvec */
 	memcgid = mem_cgroup_id(lruvec_memcg(lruvec));
 	eviction = atomic_long_read(&lruvec->nonresident_age);
+	eviction >>= bucket_order;
+	eviction = (eviction << WORKINGSET_WIDTH) | PageWorkingset(page);
 	workingset_age_nonresident(lruvec, thp_nr_pages(page));
-	return pack_shadow(memcgid, pgdat, eviction, PageWorkingset(page));
+	return pack_shadow(memcgid, pgdat, eviction);
 }
 
 /**
@@ -294,7 +283,7 @@ void workingset_refault(struct page *page, void *shadow)
 	bool workingset;
 	int memcgid;
 
-	unpack_shadow(shadow, &memcgid, &pgdat, &eviction, &workingset);
+	eviction = unpack_shadow(shadow, &memcgid, &pgdat);
 
 	rcu_read_lock();
 	/*
@@ -318,6 +307,8 @@ void workingset_refault(struct page *page, void *shadow)
 		goto out;
 	eviction_lruvec = mem_cgroup_lruvec(eviction_memcg, pgdat);
 	refault = atomic_long_read(&eviction_lruvec->nonresident_age);
+	workingset = eviction & (BIT(WORKINGSET_WIDTH) - 1);
+	eviction = (eviction >> WORKINGSET_WIDTH) << bucket_order;
 
 	/*
 	 * Calculate the refault distance
@@ -335,7 +326,7 @@ void workingset_refault(struct page *page, void *shadow)
 	 * longest time, so the occasional inappropriate activation
 	 * leading to pressure on the active list is not a problem.
 	 */
-	refault_distance = (refault - eviction) & EVICTION_MASK;
+	refault_distance = (refault - eviction) & (EVICTION_MASK >> WORKINGSET_WIDTH);
 
 	/*
 	 * The activation decision for this page is made at the level
@@ -593,7 +584,7 @@ static int __init workingset_init(void)
 	unsigned int max_order;
 	int ret;
 
-	BUILD_BUG_ON(BITS_PER_LONG < EVICTION_SHIFT);
+	BUILD_BUG_ON(EVICTION_SHIFT < WORKINGSET_WIDTH);
 	/*
 	 * Calculate the eviction bucket size to cover the longest
 	 * actionable refault distance, which is currently half of
@@ -601,7 +592,7 @@ static int __init workingset_init(void)
 	 * some more pages at runtime, so keep working with up to
 	 * double the initial memory by using totalram_pages as-is.
 	 */
-	timestamp_bits = BITS_PER_LONG - EVICTION_SHIFT;
+	timestamp_bits = EVICTION_SHIFT - WORKINGSET_WIDTH;
 	max_order = fls_long(totalram_pages() - 1);
 	if (max_order > timestamp_bits)
 		bucket_order = max_order - timestamp_bits;
-- 
2.31.1.751.gd2f1c929bd-goog

[PATCH v3 07/14] mm: multigenerational lru: groundwork

[Yu Zhao]

For each lruvec, evictable pages are divided into multiple
generations. The youngest generation number is stored in
lrugen->max_seq for both anon and file types as they are aged on an
equal footing. The oldest generation numbers are stored in
lrugen->min_seq[2] separately for anon and file types as clean file
pages can be evicted regardless of may_swap or may_writepage. These
three variables are monotonically increasing. Generation numbers are
truncated into order_base_2(MAX_NR_GENS+1) bits in order to fit into
page->flags. The sliding window technique is used to prevent truncated
generation numbers from overlapping. Each truncated generation number
is an index to
lrugen->lists[MAX_NR_GENS][ANON_AND_FILE][MAX_NR_ZONES]. Evictable
pages are added to the per-zone lists indexed by lrugen->max_seq or
lrugen->min_seq[2] (modulo MAX_NR_GENS), depending on their types.

Each generation is then divided into multiple tiers. Tiers represent
levels of usage from file descriptors only. Pages accessed N times via
file descriptors belong to tier order_base_2(N). Each generation
contains at most MAX_NR_TIERS tiers, and they require additional
MAX_NR_TIERS-2 bits in page->flags. In contrast to moving across
generations which requires the lru lock for the list operations,
moving across tiers only involves an atomic operation on page->flags
and therefore has a negligible cost. A feedback loop modeled after the
PID controller monitors the refault rates across all tiers and decides
when to activate pages from which tiers in the reclaim path.

The framework comprises two conceptually independent components: the
aging and the eviction, which can be invoked separately from user
space for the purpose of working set estimation and proactive reclaim.

The aging produces young generations. Given an lruvec, the aging scans
page tables for referenced pages of this lruvec. Upon finding one, the
aging updates its generation number to max_seq. After each round of
scan, the aging increments max_seq. The aging is due when both of
min_seq[2] reaches max_seq-1, assuming both anon and file types are
reclaimable.

The eviction consumes old generations. Given an lruvec, the eviction
scans the pages on the per-zone lists indexed by either of min_seq[2].
It tries to select a type based on the values of min_seq[2] and
swappiness. During a scan, the eviction sorts pages according to their
new generation numbers, if the aging has found them referenced. When
it finds all the per-zone lists of a selected type are empty, the
eviction increments min_seq[2] indexed by this selected type.

Signed-off-by: Yu Zhao <yuzhao@google.com>
Tested-by: Konstantin Kharlamov <Hi-Angel@yandex.ru>
---
 fs/fuse/dev.c                     |   3 +-
 include/linux/mm.h                |   2 +
 include/linux/mm_inline.h         | 194 +++++++++++++++++++
 include/linux/mmzone.h            | 106 +++++++++++
 include/linux/page-flags-layout.h |  19 +-
 include/linux/page-flags.h        |   4 +-
 kernel/bounds.c                   |   6 +
 mm/huge_memory.c                  |   3 +-
 mm/mm_init.c                      |   6 +-
 mm/mmzone.c                       |   2 +
 mm/swapfile.c                     |   4 +
 mm/vmscan.c                       | 306 ++++++++++++++++++++++++++++++
 12 files changed, 644 insertions(+), 11 deletions(-)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index a5ceccc5ef00..f784c118f00f 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -784,7 +784,8 @@ static int fuse_check_page(struct page *page)
 	       1 << PG_lru |
 	       1 << PG_active |
 	       1 << PG_reclaim |
-	       1 << PG_waiters))) {
+	       1 << PG_waiters |
+	       LRU_GEN_MASK | LRU_USAGE_MASK))) {
 		dump_page(page, "fuse: trying to steal weird page");
 		return 1;
 	}
diff --git a/include/linux/mm.h b/include/linux/mm.h
index c274f75efcf9..e0c19a02db9d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1089,6 +1089,8 @@ vm_fault_t finish_mkwrite_fault(struct vm_fault *vmf);
 #define ZONES_PGOFF		(NODES_PGOFF - ZONES_WIDTH)
 #define LAST_CPUPID_PGOFF	(ZONES_PGOFF - LAST_CPUPID_WIDTH)
 #define KASAN_TAG_PGOFF		(LAST_CPUPID_PGOFF - KASAN_TAG_WIDTH)
+#define LRU_GEN_PGOFF		(KASAN_TAG_PGOFF - LRU_GEN_WIDTH)
+#define LRU_USAGE_PGOFF		(LRU_GEN_PGOFF - LRU_USAGE_WIDTH)
 
 /*
  * Define the bit shifts to access each section.  For non-existent
diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
index 355ea1ee32bd..ae3e3826dd7f 100644
--- a/include/linux/mm_inline.h
+++ b/include/linux/mm_inline.h
@@ -79,11 +79,199 @@ static __always_inline enum lru_list page_lru(struct page *page)
 	return lru;
 }
 
+#ifdef CONFIG_LRU_GEN
+
+#ifdef CONFIG_LRU_GEN_ENABLED
+DECLARE_STATIC_KEY_TRUE(lru_gen_static_key);
+
+static inline bool lru_gen_enabled(void)
+{
+	return static_branch_likely(&lru_gen_static_key);
+}
+#else
+DECLARE_STATIC_KEY_FALSE(lru_gen_static_key);
+
+static inline bool lru_gen_enabled(void)
+{
+	return static_branch_unlikely(&lru_gen_static_key);
+}
+#endif
+
+/* We track at most MAX_NR_GENS generations using the sliding window technique. */
+static inline int lru_gen_from_seq(unsigned long seq)
+{
+	return seq % MAX_NR_GENS;
+}
+
+/* Return a proper index regardless whether we keep a full history of stats. */
+static inline int hist_from_seq_or_gen(int seq_or_gen)
+{
+	return seq_or_gen % NR_STAT_GENS;
+}
+
+/* The youngest and the second youngest generations are counted as active. */
+static inline bool lru_gen_is_active(struct lruvec *lruvec, int gen)
+{
+	unsigned long max_seq = READ_ONCE(lruvec->evictable.max_seq);
+
+	VM_BUG_ON(!max_seq);
+	VM_BUG_ON(gen >= MAX_NR_GENS);
+
+	return gen == lru_gen_from_seq(max_seq) || gen == lru_gen_from_seq(max_seq - 1);
+}
+
+/* Update the sizes of the multigenerational lru lists. */
+static inline void lru_gen_update_size(struct page *page, struct lruvec *lruvec,
+				       int old_gen, int new_gen)
+{
+	int type = page_is_file_lru(page);
+	int zone = page_zonenum(page);
+	int delta = thp_nr_pages(page);
+	enum lru_list lru = type * LRU_FILE;
+	struct lrugen *lrugen = &lruvec->evictable;
+
+	lockdep_assert_held(&lruvec->lru_lock);
+	VM_BUG_ON(old_gen != -1 && old_gen >= MAX_NR_GENS);
+	VM_BUG_ON(new_gen != -1 && new_gen >= MAX_NR_GENS);
+	VM_BUG_ON(old_gen == -1 && new_gen == -1);
+
+	if (old_gen >= 0)
+		WRITE_ONCE(lrugen->sizes[old_gen][type][zone],
+			   lrugen->sizes[old_gen][type][zone] - delta);
+	if (new_gen >= 0)
+		WRITE_ONCE(lrugen->sizes[new_gen][type][zone],
+			   lrugen->sizes[new_gen][type][zone] + delta);
+
+	if (old_gen < 0) {
+		if (lru_gen_is_active(lruvec, new_gen))
+			lru += LRU_ACTIVE;
+		update_lru_size(lruvec, lru, zone, delta);
+		return;
+	}
+
+	if (new_gen < 0) {
+		if (lru_gen_is_active(lruvec, old_gen))
+			lru += LRU_ACTIVE;
+		update_lru_size(lruvec, lru, zone, -delta);
+		return;
+	}
+
+	if (!lru_gen_is_active(lruvec, old_gen) && lru_gen_is_active(lruvec, new_gen)) {
+		update_lru_size(lruvec, lru, zone, -delta);
+		update_lru_size(lruvec, lru + LRU_ACTIVE, zone, delta);
+	}
+
+	VM_BUG_ON(lru_gen_is_active(lruvec, old_gen) && !lru_gen_is_active(lruvec, new_gen));
+}
+
+/* Add a page to one of the multigenerational lru lists. Return true on success. */
+static inline bool lru_gen_addition(struct page *page, struct lruvec *lruvec, bool front)
+{
+	int gen;
+	unsigned long old_flags, new_flags;
+	int type = page_is_file_lru(page);
+	int zone = page_zonenum(page);
+	struct lrugen *lrugen = &lruvec->evictable;
+
+	if (PageUnevictable(page) || !lrugen->enabled[type])
+		return false;
+	/*
+	 * If a page is being faulted in, add it to the youngest generation.
+	 * try_walk_mm_list() may look at the size of the youngest generation to
+	 * determine if the aging is due.
+	 *
+	 * If a page can't be evicted immediately, i.e., an anon page not in
+	 * swap cache, a dirty file page under reclaim, or a page rejected by
+	 * evict_pages() due to races, dirty buffer heads, etc., add it to the
+	 * second oldest generation.
+	 *
+	 * If a page could be evicted immediately, i.e., a clean file page, add
+	 * it to the oldest generation.
+	 */
+	if (PageActive(page))
+		gen = lru_gen_from_seq(lrugen->max_seq);
+	else if ((!type && !PageSwapCache(page)) ||
+		 (PageReclaim(page) && (PageDirty(page) || PageWriteback(page))) ||
+		 (!PageReferenced(page) && PageWorkingset(page)))
+		gen = lru_gen_from_seq(lrugen->min_seq[type] + 1);
+	else
+		gen = lru_gen_from_seq(lrugen->min_seq[type]);
+
+	do {
+		old_flags = READ_ONCE(page->flags);
+		VM_BUG_ON_PAGE(old_flags & LRU_GEN_MASK, page);
+
+		new_flags = (old_flags & ~(LRU_GEN_MASK | BIT(PG_active))) |
+			    ((gen + 1UL) << LRU_GEN_PGOFF);
+		/* see the comment in evict_pages() */
+		if (!(old_flags & BIT(PG_referenced)))
+			new_flags &= ~(LRU_USAGE_MASK | LRU_TIER_FLAGS);
+	} while (cmpxchg(&page->flags, old_flags, new_flags) != old_flags);
+
+	lru_gen_update_size(page, lruvec, -1, gen);
+	if (front)
+		list_add(&page->lru, &lrugen->lists[gen][type][zone]);
+	else
+		list_add_tail(&page->lru, &lrugen->lists[gen][type][zone]);
+
+	return true;
+}
+
+/* Delete a page from one of the multigenerational lru lists. Return true on success. */
+static inline bool lru_gen_deletion(struct page *page, struct lruvec *lruvec)
+{
+	int gen;
+	unsigned long old_flags, new_flags;
+
+	do {
+		old_flags = READ_ONCE(page->flags);
+		if (!(old_flags & LRU_GEN_MASK))
+			return false;
+
+		VM_BUG_ON_PAGE(PageActive(page), page);
+		VM_BUG_ON_PAGE(PageUnevictable(page), page);
+
+		gen = ((old_flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1;
+
+		new_flags = old_flags & ~LRU_GEN_MASK;
+		/* mark page active accordingly */
+		if (lru_gen_is_active(lruvec, gen))
+			new_flags |= BIT(PG_active);
+	} while (cmpxchg(&page->flags, old_flags, new_flags) != old_flags);
+
+	lru_gen_update_size(page, lruvec, gen, -1);
+	list_del(&page->lru);
+
+	return true;
+}
+
+#else /* CONFIG_LRU_GEN */
+
+static inline bool lru_gen_enabled(void)
+{
+	return false;
+}
+
+static inline bool lru_gen_addition(struct page *page, struct lruvec *lruvec, bool front)
+{
+	return false;
+}
+
+static inline bool lru_gen_deletion(struct page *page, struct lruvec *lruvec)
+{
+	return false;
+}
+
+#endif /* CONFIG_LRU_GEN */
+
 static __always_inline void add_page_to_lru_list(struct page *page,
 				struct lruvec *lruvec)
 {
 	enum lru_list lru = page_lru(page);
 
+	if (lru_gen_addition(page, lruvec, true))
+		return;
+
 	update_lru_size(lruvec, lru, page_zonenum(page), thp_nr_pages(page));
 	list_add(&page->lru, &lruvec->lists[lru]);
 }
@@ -93,6 +281,9 @@ static __always_inline void add_page_to_lru_list_tail(struct page *page,
 {
 	enum lru_list lru = page_lru(page);
 
+	if (lru_gen_addition(page, lruvec, false))
+		return;
+
 	update_lru_size(lruvec, lru, page_zonenum(page), thp_nr_pages(page));
 	list_add_tail(&page->lru, &lruvec->lists[lru]);
 }
@@ -100,6 +291,9 @@ static __always_inline void add_page_to_lru_list_tail(struct page *page,
 static __always_inline void del_page_from_lru_list(struct page *page,
 				struct lruvec *lruvec)
 {
+	if (lru_gen_deletion(page, lruvec))
+		return;
+
 	list_del(&page->lru);
 	update_lru_size(lruvec, page_lru(page), page_zonenum(page),
 			-thp_nr_pages(page));
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 0d53eba1c383..e5deec17b4bd 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -293,6 +293,108 @@ enum lruvec_flags {
 					 */
 };
 
+struct lruvec;
+
+#define LRU_GEN_MASK		((BIT(LRU_GEN_WIDTH) - 1) << LRU_GEN_PGOFF)
+#define LRU_USAGE_MASK		((BIT(LRU_USAGE_WIDTH) - 1) << LRU_USAGE_PGOFF)
+
+#ifdef CONFIG_LRU_GEN
+
+/*
+ * For each lruvec, evictable pages are divided into multiple generations. The
+ * youngest and the oldest generation numbers, AKA max_seq and min_seq, are
+ * monotonically increasing. The sliding window technique is used to track at
+ * most MAX_NR_GENS and at least MIN_NR_GENS generations. An offset within the
+ * window, AKA gen, indexes an array of per-type and per-zone lists for the
+ * corresponding generation. The counter in page->flags stores gen+1 while a
+ * page is on one of the multigenerational lru lists. Otherwise, it stores 0.
+ */
+#define MAX_NR_GENS		((unsigned int)CONFIG_NR_LRU_GENS)
+
+/*
+ * Each generation is then divided into multiple tiers. Tiers represent levels
+ * of usage from file descriptors, i.e., mark_page_accessed(). In contrast to
+ * moving across generations which requires the lru lock, moving across tiers
+ * only involves an atomic operation on page->flags and therefore has a
+ * negligible cost.
+ *
+ * The purposes of tiers are to:
+ *   1) estimate whether pages accessed multiple times via file descriptors are
+ *   more active than pages accessed only via page tables by separating the two
+ *   access types into upper tiers and the base tier and comparing refault rates
+ *   across tiers.
+ *   2) improve buffered io performance by deferring activations of pages
+ *   accessed multiple times until the eviction. That is activations happen in
+ *   the reclaim path, not the access path.
+ *
+ * Pages accessed N times via file descriptors belong to tier order_base_2(N).
+ * The base tier uses the following page flag:
+ *   !PageReferenced() -- readahead pages
+ *   PageReferenced() -- single-access pages
+ * All upper tiers use the following page flags:
+ *   PageReferenced() && PageWorkingset() -- multi-access pages
+ * in addition to the bits storing N-2 accesses. Therefore, we can support one
+ * upper tier without using additional bits in page->flags.
+ *
+ * Note that
+ *   1) PageWorkingset() is always set for upper tiers because we want to
+ *    maintain the existing psi behavior.
+ *   2) !PageReferenced() && PageWorkingset() is not a valid tier. See the
+ *   comment in evict_pages().
+ *
+ * Pages from the base tier are evicted regardless of its refault rate. Pages
+ * from upper tiers will be moved to the next generation, if their refault rates
+ * are higher than that of the base tier.
+ */
+#define MAX_NR_TIERS		((unsigned int)CONFIG_TIERS_PER_GEN)
+#define LRU_TIER_FLAGS		(BIT(PG_referenced) | BIT(PG_workingset))
+#define LRU_USAGE_SHIFT		(CONFIG_TIERS_PER_GEN - 1)
+
+/* Whether to keep historical stats for each generation. */
+#ifdef CONFIG_LRU_GEN_STATS
+#define NR_STAT_GENS		((unsigned int)CONFIG_NR_LRU_GENS)
+#else
+#define NR_STAT_GENS		1U
+#endif
+
+struct lrugen {
+	/* the aging increments the max generation number */
+	unsigned long max_seq;
+	/* the eviction increments the min generation numbers */
+	unsigned long min_seq[ANON_AND_FILE];
+	/* the birth time of each generation in jiffies */
+	unsigned long timestamps[MAX_NR_GENS];
+	/* the multigenerational lru lists */
+	struct list_head lists[MAX_NR_GENS][ANON_AND_FILE][MAX_NR_ZONES];
+	/* the sizes of the multigenerational lru lists in pages */
+	unsigned long sizes[MAX_NR_GENS][ANON_AND_FILE][MAX_NR_ZONES];
+	/* to determine which type and its tiers to evict */
+	atomic_long_t evicted[NR_STAT_GENS][ANON_AND_FILE][MAX_NR_TIERS];
+	atomic_long_t refaulted[NR_STAT_GENS][ANON_AND_FILE][MAX_NR_TIERS];
+	/* the base tier won't be activated */
+	unsigned long activated[NR_STAT_GENS][ANON_AND_FILE][MAX_NR_TIERS - 1];
+	/* arithmetic mean weighted by geometric series 1/2, 1/4, ... */
+	unsigned long avg_total[ANON_AND_FILE][MAX_NR_TIERS];
+	unsigned long avg_refaulted[ANON_AND_FILE][MAX_NR_TIERS];
+	/* whether the multigenerational lru is enabled */
+	bool enabled[ANON_AND_FILE];
+};
+
+void lru_gen_init_lruvec(struct lruvec *lruvec);
+void lru_gen_set_state(bool enable, bool main, bool swap);
+
+#else /* CONFIG_LRU_GEN */
+
+static inline void lru_gen_init_lruvec(struct lruvec *lruvec)
+{
+}
+
+static inline void lru_gen_set_state(bool enable, bool main, bool swap)
+{
+}
+
+#endif /* CONFIG_LRU_GEN */
+
 struct lruvec {
 	struct list_head		lists[NR_LRU_LISTS];
 	/* per lruvec lru_lock for memcg */
@@ -310,6 +412,10 @@ struct lruvec {
 	unsigned long			refaults[ANON_AND_FILE];
 	/* Various lruvec state flags (enum lruvec_flags) */
 	unsigned long			flags;
+#ifdef CONFIG_LRU_GEN
+	/* unevictable pages are on LRU_UNEVICTABLE */
+	struct lrugen			evictable;
+#endif
 #ifdef CONFIG_MEMCG
 	struct pglist_data *pgdat;
 #endif
diff --git a/include/linux/page-flags-layout.h b/include/linux/page-flags-layout.h
index ef1e3e736e14..ce8d5732a3aa 100644
--- a/include/linux/page-flags-layout.h
+++ b/include/linux/page-flags-layout.h
@@ -26,6 +26,14 @@
 
 #define ZONES_WIDTH		ZONES_SHIFT
 
+#ifdef CONFIG_LRU_GEN
+/* LRU_GEN_WIDTH is generated from order_base_2(CONFIG_NR_LRU_GENS + 1). */
+#define LRU_USAGE_WIDTH		(CONFIG_TIERS_PER_GEN - 2)
+#else
+#define LRU_GEN_WIDTH		0
+#define LRU_USAGE_WIDTH		0
+#endif
+
 #ifdef CONFIG_SPARSEMEM
 #include <asm/sparsemem.h>
 #define SECTIONS_SHIFT	(MAX_PHYSMEM_BITS - SECTION_SIZE_BITS)
@@ -55,7 +63,8 @@
 #define SECTIONS_WIDTH		0
 #endif
 
-#if ZONES_WIDTH + SECTIONS_WIDTH + NODES_SHIFT <= BITS_PER_LONG - NR_PAGEFLAGS
+#if ZONES_WIDTH + LRU_GEN_WIDTH + LRU_USAGE_WIDTH + SECTIONS_WIDTH + NODES_SHIFT \
+	<= BITS_PER_LONG - NR_PAGEFLAGS
 #define NODES_WIDTH		NODES_SHIFT
 #elif defined(CONFIG_SPARSEMEM_VMEMMAP)
 #error "Vmemmap: No space for nodes field in page flags"
@@ -89,8 +98,8 @@
 #define LAST_CPUPID_SHIFT 0
 #endif
 
-#if ZONES_WIDTH + SECTIONS_WIDTH + NODES_WIDTH + KASAN_TAG_WIDTH + LAST_CPUPID_SHIFT \
-	<= BITS_PER_LONG - NR_PAGEFLAGS
+#if ZONES_WIDTH + LRU_GEN_WIDTH + LRU_USAGE_WIDTH + SECTIONS_WIDTH + NODES_WIDTH + \
+	KASAN_TAG_WIDTH + LAST_CPUPID_SHIFT <= BITS_PER_LONG - NR_PAGEFLAGS
 #define LAST_CPUPID_WIDTH LAST_CPUPID_SHIFT
 #else
 #define LAST_CPUPID_WIDTH 0
@@ -100,8 +109,8 @@
 #define LAST_CPUPID_NOT_IN_PAGE_FLAGS
 #endif
 
-#if ZONES_WIDTH + SECTIONS_WIDTH + NODES_WIDTH + KASAN_TAG_WIDTH + LAST_CPUPID_WIDTH \
-	> BITS_PER_LONG - NR_PAGEFLAGS
+#if ZONES_WIDTH + LRU_GEN_WIDTH + LRU_USAGE_WIDTH + SECTIONS_WIDTH + NODES_WIDTH + \
+	KASAN_TAG_WIDTH + LAST_CPUPID_WIDTH > BITS_PER_LONG - NR_PAGEFLAGS
 #error "Not enough bits in page flags"
 #endif
 
diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 04a34c08e0a6..e58984fca32a 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -817,7 +817,7 @@ static inline void ClearPageSlabPfmemalloc(struct page *page)
 	 1UL << PG_private	| 1UL << PG_private_2	|	\
 	 1UL << PG_writeback	| 1UL << PG_reserved	|	\
 	 1UL << PG_slab		| 1UL << PG_active 	|	\
-	 1UL << PG_unevictable	| __PG_MLOCKED)
+	 1UL << PG_unevictable	| __PG_MLOCKED | LRU_GEN_MASK)
 
 /*
  * Flags checked when a page is prepped for return by the page allocator.
@@ -828,7 +828,7 @@ static inline void ClearPageSlabPfmemalloc(struct page *page)
  * alloc-free cycle to prevent from reusing the page.
  */
 #define PAGE_FLAGS_CHECK_AT_PREP	\
-	(((1UL << NR_PAGEFLAGS) - 1) & ~__PG_HWPOISON)
+	((((1UL << NR_PAGEFLAGS) - 1) & ~__PG_HWPOISON) | LRU_GEN_MASK | LRU_USAGE_MASK)
 
 #define PAGE_FLAGS_PRIVATE				\
 	(1UL << PG_private | 1UL << PG_private_2)
diff --git a/kernel/bounds.c b/kernel/bounds.c
index 9795d75b09b2..a8cbf2d0b11a 100644
--- a/kernel/bounds.c
+++ b/kernel/bounds.c
@@ -22,6 +22,12 @@ int main(void)
 	DEFINE(NR_CPUS_BITS, ilog2(CONFIG_NR_CPUS));
 #endif
 	DEFINE(SPINLOCK_SIZE, sizeof(spinlock_t));
+#ifdef CONFIG_LRU_GEN
+	/* bits needed to represent internal values stored in page->flags */
+	DEFINE(LRU_GEN_WIDTH, order_base_2(CONFIG_NR_LRU_GENS + 1));
+	/* bits needed to represent normalized values for external uses */
+	DEFINE(LRU_GEN_SHIFT, order_base_2(CONFIG_NR_LRU_GENS));
+#endif
 	/* End of constants */
 
 	return 0;
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 63ed6b25deaa..8ac9093e5a0d 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2410,7 +2410,8 @@ static void __split_huge_page_tail(struct page *head, int tail,
 #ifdef CONFIG_64BIT
 			 (1L << PG_arch_2) |
 #endif
-			 (1L << PG_dirty)));
+			 (1L << PG_dirty) |
+			 LRU_GEN_MASK | LRU_USAGE_MASK));
 
 	/* ->mapping in first tail page is compound_mapcount */
 	VM_BUG_ON_PAGE(tail > 2 && page_tail->mapping != TAIL_MAPPING,
diff --git a/mm/mm_init.c b/mm/mm_init.c
index 9ddaf0e1b0ab..ef0deadb90a7 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -65,14 +65,16 @@ void __init mminit_verify_pageflags_layout(void)
 
 	shift = 8 * sizeof(unsigned long);
 	width = shift - SECTIONS_WIDTH - NODES_WIDTH - ZONES_WIDTH
-		- LAST_CPUPID_SHIFT - KASAN_TAG_WIDTH;
+		- LAST_CPUPID_SHIFT - KASAN_TAG_WIDTH - LRU_GEN_WIDTH - LRU_USAGE_WIDTH;
 	mminit_dprintk(MMINIT_TRACE, "pageflags_layout_widths",
-		"Section %d Node %d Zone %d Lastcpupid %d Kasantag %d Flags %d\n",
+		"Section %d Node %d Zone %d Lastcpupid %d Kasantag %d Gen %d Tier %d Flags %d\n",
 		SECTIONS_WIDTH,
 		NODES_WIDTH,
 		ZONES_WIDTH,
 		LAST_CPUPID_WIDTH,
 		KASAN_TAG_WIDTH,
+		LRU_GEN_WIDTH,
+		LRU_USAGE_WIDTH,
 		NR_PAGEFLAGS);
 	mminit_dprintk(MMINIT_TRACE, "pageflags_layout_shifts",
 		"Section %d Node %d Zone %d Lastcpupid %d Kasantag %d\n",
diff --git a/mm/mmzone.c b/mm/mmzone.c
index eb89d6e018e2..2ec0d7793424 100644
--- a/mm/mmzone.c
+++ b/mm/mmzone.c
@@ -81,6 +81,8 @@ void lruvec_init(struct lruvec *lruvec)
 
 	for_each_lru(lru)
 		INIT_LIST_HEAD(&lruvec->lists[lru]);
+
+	lru_gen_init_lruvec(lruvec);
 }
 
 #if defined(CONFIG_NUMA_BALANCING) && !defined(LAST_CPUPID_NOT_IN_PAGE_FLAGS)
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 149e77454e3c..3598b668f533 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -2702,6 +2702,8 @@ SYSCALL_DEFINE1(swapoff, const char __user *, specialfile)
 	err = 0;
 	atomic_inc(&proc_poll_event);
 	wake_up_interruptible(&proc_poll_wait);
+	/* stop tracking anon if the multigenerational lru is turned off */
+	lru_gen_set_state(false, false, true);
 
 out_dput:
 	filp_close(victim, NULL);
@@ -3348,6 +3350,8 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 	mutex_unlock(&swapon_mutex);
 	atomic_inc(&proc_poll_event);
 	wake_up_interruptible(&proc_poll_wait);
+	/* start tracking anon if the multigenerational lru is turned on */
+	lru_gen_set_state(true, false, true);
 
 	error = 0;
 	goto out;
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2339459c97d4..f7bbfc0b1ebd 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -49,6 +49,7 @@
 #include <linux/printk.h>
 #include <linux/dax.h>
 #include <linux/psi.h>
+#include <linux/memory.h>
 
 #include <asm/tlbflush.h>
 #include <asm/div64.h>
@@ -2715,6 +2716,311 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
 	}
 }
 
+#ifdef CONFIG_LRU_GEN
+
+/*
+ * After pages are faulted in, the aging must scan them twice before the
+ * eviction can consider them. The first scan clears the accessed bit set during
+ * initial faults. And the second scan makes sure they haven't been used since
+ * the first scan.
+ */
+#define MIN_NR_GENS	2
+
+#define MAX_BATCH_SIZE	8192
+
+/******************************************************************************
+ *                          shorthand helpers
+ ******************************************************************************/
+
+#define DEFINE_MAX_SEQ()						\
+	unsigned long max_seq = READ_ONCE(lruvec->evictable.max_seq)
+
+#define DEFINE_MIN_SEQ()						\
+	unsigned long min_seq[ANON_AND_FILE] = {			\
+		READ_ONCE(lruvec->evictable.min_seq[0]),		\
+		READ_ONCE(lruvec->evictable.min_seq[1]),		\
+	}
+
+#define for_each_type_zone(type, zone)					\
+	for ((type) = 0; (type) < ANON_AND_FILE; (type)++)		\
+		for ((zone) = 0; (zone) < MAX_NR_ZONES; (zone)++)
+
+#define for_each_gen_type_zone(gen, type, zone)				\
+	for ((gen) = 0; (gen) < MAX_NR_GENS; (gen)++)			\
+		for ((type) = 0; (type) < ANON_AND_FILE; (type)++)	\
+			for ((zone) = 0; (zone) < MAX_NR_ZONES; (zone)++)
+
+static int page_lru_gen(struct page *page)
+{
+	return ((page->flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1;
+}
+
+static int get_nr_gens(struct lruvec *lruvec, int type)
+{
+	return lruvec->evictable.max_seq - lruvec->evictable.min_seq[type] + 1;
+}
+
+static int min_nr_gens(unsigned long max_seq, unsigned long *min_seq, int swappiness)
+{
+	return max_seq - max(min_seq[!swappiness], min_seq[1]) + 1;
+}
+
+static int max_nr_gens(unsigned long max_seq, unsigned long *min_seq, int swappiness)
+{
+	return max_seq - min(min_seq[!swappiness], min_seq[1]) + 1;
+}
+
+static bool __maybe_unused seq_is_valid(struct lruvec *lruvec)
+{
+	lockdep_assert_held(&lruvec->lru_lock);
+
+	return get_nr_gens(lruvec, 0) >= MIN_NR_GENS &&
+	       get_nr_gens(lruvec, 0) <= MAX_NR_GENS &&
+	       get_nr_gens(lruvec, 1) >= MIN_NR_GENS &&
+	       get_nr_gens(lruvec, 1) <= MAX_NR_GENS;
+}
+
+/******************************************************************************
+ *                          state change
+ ******************************************************************************/
+
+#ifdef CONFIG_LRU_GEN_ENABLED
+DEFINE_STATIC_KEY_TRUE(lru_gen_static_key);
+#else
+DEFINE_STATIC_KEY_FALSE(lru_gen_static_key);
+#endif
+
+static DEFINE_MUTEX(lru_gen_state_mutex);
+static int lru_gen_nr_swapfiles __read_mostly;
+
+static bool __maybe_unused state_is_valid(struct lruvec *lruvec)
+{
+	int gen, type, zone;
+	enum lru_list lru;
+	struct lrugen *lrugen = &lruvec->evictable;
+
+	for_each_evictable_lru(lru) {
+		type = is_file_lru(lru);
+
+		if (lrugen->enabled[type] && !list_empty(&lruvec->lists[lru]))
+			return false;
+	}
+
+	for_each_gen_type_zone(gen, type, zone) {
+		if (!lrugen->enabled[type] && !list_empty(&lrugen->lists[gen][type][zone]))
+			return false;
+
+		VM_WARN_ON_ONCE(!lrugen->enabled[type] && lrugen->sizes[gen][type][zone]);
+	}
+
+	return true;
+}
+
+static bool fill_lru_gen_lists(struct lruvec *lruvec)
+{
+	enum lru_list lru;
+	int batch_size = 0;
+
+	for_each_evictable_lru(lru) {
+		int type = is_file_lru(lru);
+		bool active = is_active_lru(lru);
+		struct list_head *head = &lruvec->lists[lru];
+
+		if (!lruvec->evictable.enabled[type])
+			continue;
+
+		while (!list_empty(head)) {
+			bool success;
+			struct page *page = lru_to_page(head);
+
+			VM_BUG_ON_PAGE(PageTail(page), page);
+			VM_BUG_ON_PAGE(PageUnevictable(page), page);
+			VM_BUG_ON_PAGE(PageActive(page) != active, page);
+			VM_BUG_ON_PAGE(page_lru_gen(page) != -1, page);
+			VM_BUG_ON_PAGE(page_is_file_lru(page) != type, page);
+
+			prefetchw_prev_lru_page(page, head, flags);
+
+			del_page_from_lru_list(page, lruvec);
+			success = lru_gen_addition(page, lruvec, true);
+			VM_BUG_ON(!success);
+
+			if (++batch_size == MAX_BATCH_SIZE)
+				return false;
+		}
+	}
+
+	return true;
+}
+
+static bool drain_lru_gen_lists(struct lruvec *lruvec)
+{
+	int gen, type, zone;
+	int batch_size = 0;
+
+	for_each_gen_type_zone(gen, type, zone) {
+		struct list_head *head = &lruvec->evictable.lists[gen][type][zone];
+
+		if (lruvec->evictable.enabled[type])
+			continue;
+
+		while (!list_empty(head)) {
+			bool success;
+			struct page *page = lru_to_page(head);
+
+			VM_BUG_ON_PAGE(PageTail(page), page);
+			VM_BUG_ON_PAGE(PageUnevictable(page), page);
+			VM_BUG_ON_PAGE(PageActive(page), page);
+			VM_BUG_ON_PAGE(page_is_file_lru(page) != type, page);
+			VM_BUG_ON_PAGE(page_zonenum(page) != zone, page);
+
+			prefetchw_prev_lru_page(page, head, flags);
+
+			success = lru_gen_deletion(page, lruvec);
+			VM_BUG_ON(!success);
+			add_page_to_lru_list(page, lruvec);
+
+			if (++batch_size == MAX_BATCH_SIZE)
+				return false;
+		}
+	}
+
+	return true;
+}
+
+/*
+ * For file page tracking, we enable/disable it according to the main switch.
+ * For anon page tracking, we only enabled it when the main switch is on and
+ * there is at least one swapfile; we disable it when there are no swapfiles
+ * regardless of the value of the main switch. Otherwise, we will eventually
+ * reach the max size of the sliding window and have to call inc_min_seq(),
+ * which brings an unnecessary overhead.
+ */
+void lru_gen_set_state(bool enable, bool main, bool swap)
+{
+	struct mem_cgroup *memcg;
+
+	mem_hotplug_begin();
+	mutex_lock(&lru_gen_state_mutex);
+	cgroup_lock();
+
+	main = main && enable != lru_gen_enabled();
+	swap = swap && !(enable ? lru_gen_nr_swapfiles++ : --lru_gen_nr_swapfiles);
+	swap = swap && lru_gen_enabled();
+	if (!main && !swap)
+		goto unlock;
+
+	if (main) {
+		if (enable)
+			static_branch_enable(&lru_gen_static_key);
+		else
+			static_branch_disable(&lru_gen_static_key);
+	}
+
+	memcg = mem_cgroup_iter(NULL, NULL, NULL);
+	do {
+		int nid;
+
+		for_each_node_state(nid, N_MEMORY) {
+			struct lruvec *lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(nid));
+			struct lrugen *lrugen = &lruvec->evictable;
+
+			spin_lock_irq(&lruvec->lru_lock);
+
+			VM_BUG_ON(!seq_is_valid(lruvec));
+			VM_BUG_ON(!state_is_valid(lruvec));
+
+			WRITE_ONCE(lrugen->enabled[0], lru_gen_enabled() && lru_gen_nr_swapfiles);
+			WRITE_ONCE(lrugen->enabled[1], lru_gen_enabled());
+
+			while (!(enable ? fill_lru_gen_lists(lruvec) :
+					  drain_lru_gen_lists(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:
+	cgroup_unlock();
+	mutex_unlock(&lru_gen_state_mutex);
+	mem_hotplug_done();
+}
+
+static int __meminit __maybe_unused lru_gen_online_mem(struct notifier_block *self,
+						       unsigned long action, void *arg)
+{
+	struct mem_cgroup *memcg;
+	struct memory_notify *mnb = arg;
+	int nid = mnb->status_change_nid;
+
+	if (action != MEM_GOING_ONLINE || nid == NUMA_NO_NODE)
+		return NOTIFY_DONE;
+
+	mutex_lock(&lru_gen_state_mutex);
+	cgroup_lock();
+
+	memcg = mem_cgroup_iter(NULL, NULL, NULL);
+	do {
+		struct lruvec *lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(nid));
+		struct lrugen *lrugen = &lruvec->evictable;
+
+		VM_BUG_ON(!seq_is_valid(lruvec));
+		VM_BUG_ON(!state_is_valid(lruvec));
+
+		WRITE_ONCE(lrugen->enabled[0], lru_gen_enabled() && lru_gen_nr_swapfiles);
+		WRITE_ONCE(lrugen->enabled[1], lru_gen_enabled());
+	} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)));
+
+	cgroup_unlock();
+	mutex_unlock(&lru_gen_state_mutex);
+
+	return NOTIFY_DONE;
+}
+
+/******************************************************************************
+ *                          initialization
+ ******************************************************************************/
+
+void lru_gen_init_lruvec(struct lruvec *lruvec)
+{
+	int i;
+	int gen, type, zone;
+	struct lrugen *lrugen = &lruvec->evictable;
+
+	lrugen->max_seq = MIN_NR_GENS + 1;
+	lrugen->enabled[0] = lru_gen_enabled() && lru_gen_nr_swapfiles;
+	lrugen->enabled[1] = lru_gen_enabled();
+
+	for (i = 0; i <= MIN_NR_GENS + 1; i++)
+		lrugen->timestamps[i] = jiffies;
+
+	for_each_gen_type_zone(gen, type, zone)
+		INIT_LIST_HEAD(&lrugen->lists[gen][type][zone]);
+}
+
+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 (hotplug_memory_notifier(lru_gen_online_mem, 0))
+		pr_err("lru_gen: failed to subscribe hotplug notifications\n");
+
+	return 0;
+};
+/*
+ * We want to run as early as possible because debug code may call mm_alloc()
+ * and mmput(). Out only dependency mm_kobj is initialized one stage earlier.
+ */
+arch_initcall(init_lru_gen);
+
+#endif /* CONFIG_LRU_GEN */
+
 static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
 {
 	unsigned long nr[NR_LRU_LISTS];
-- 
2.31.1.751.gd2f1c929bd-goog

[PATCH v3 08/14] mm: multigenerational lru: activation

[Yu Zhao]

For pages accessed multiple times via file descriptors, instead of
activating them upon the second access, we activate them based on the
refault rates of their tiers. Each generation contains at most
MAX_NR_TIERS tiers, and they require additional MAX_NR_TIERS-2 bits in
page->flags. Pages accessed N times via file descriptors belong to
tier order_base_2(N). Tier 0 is the base tier and it contains pages
read ahead, accessed once via file descriptors and accessed only via
page tables. Pages from the base tier are evicted regardless of the
refault rate. Pages from upper tiers that have higher refault rates
than the base tier will be moved to the next generation. A feedback
loop modeled after the PID controller monitors refault rates across
all tiers and decides when to activate pages from which upper tiers
in the reclaim path. The advantages of this model are:
  1) It has a negligible cost in the buffered IO access path because
  activations are done optionally in the reclaim path.
  2) It takes mapped pages into account and avoids overprotecting
  pages accessed multiple times via file descriptors.
  3) More tiers offer better protection to pages accessed more than
  twice when workloads doing intensive buffered IO are under memory
  pressure.

For pages mapped upon page faults, the accessed bit is set during the
initial faults. Ideally we add them to the per-zone lists index by
max_seq, i.e., the youngest generation, so that eviction will not
consider them before the aging has scanned them. For anon pages not in
swap cache, this can be done easily in the page fault path: we rename
lru_cache_add_inactive_or_unevictable() to lru_cache_add_page_vma()
and add a new parameter, which is set to true for pages mapped upon
page faults. For pages in page cache or swap cache, we cannot
differentiate the page fault path from the read ahead path at the time
we call lru_cache_add(). So we add them to the per-zone lists index by
min_seq, i.e., the oldest generation, for now.

Finally, we need to make sure deactivation works when the
multigenerational lru is enabled. We cannot use PageActive() because
it is not set on pages from active generations, in order to spare the
aging the trouble of clearing it when active generations become
inactive. So we deactivate pages unconditionally since deactivation is
not a hot code path worth additional optimizations.

Signed-off-by: Yu Zhao <yuzhao@google.com>
Tested-by: Konstantin Kharlamov <Hi-Angel@yandex.ru>
---
 include/linux/mm_inline.h |  40 ++++++++++++++
 include/linux/swap.h      |   4 +-
 kernel/events/uprobes.c   |   2 +-
 mm/huge_memory.c          |   2 +-
 mm/khugepaged.c           |   2 +-
 mm/memory.c               |  10 ++--
 mm/migrate.c              |   2 +-
 mm/swap.c                 |  22 +++++---
 mm/swapfile.c             |   2 +-
 mm/userfaultfd.c          |   2 +-
 mm/vmscan.c               |  91 ++++++++++++++++++++++++++++++-
 mm/workingset.c           | 112 ++++++++++++++++++++++++++++++++++++++
 12 files changed, 269 insertions(+), 22 deletions(-)

diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
index ae3e3826dd7f..f3b99f65a652 100644
--- a/include/linux/mm_inline.h
+++ b/include/linux/mm_inline.h
@@ -103,6 +103,12 @@ static inline int lru_gen_from_seq(unsigned long seq)
 	return seq % MAX_NR_GENS;
 }
 
+/* Convert the level of usage to a tier. See the comment on MAX_NR_TIERS. */
+static inline int lru_tier_from_usage(int usage)
+{
+	return order_base_2(usage + 1);
+}
+
 /* Return a proper index regardless whether we keep a full history of stats. */
 static inline int hist_from_seq_or_gen(int seq_or_gen)
 {
@@ -245,6 +251,36 @@ static inline bool lru_gen_deletion(struct page *page, struct lruvec *lruvec)
 	return true;
 }
 
+/* Return the level of usage of a page. See the comment on MAX_NR_TIERS. */
+static inline int page_tier_usage(struct page *page)
+{
+	unsigned long flags = READ_ONCE(page->flags);
+
+	return flags & BIT(PG_workingset) ?
+	       ((flags & LRU_USAGE_MASK) >> LRU_USAGE_PGOFF) + 1 : 0;
+}
+
+/* Increment the usage counter after a page is accessed via file descriptors. */
+static inline void page_inc_usage(struct page *page)
+{
+	unsigned long usage;
+	unsigned long old_flags, new_flags;
+
+	do {
+		old_flags = READ_ONCE(page->flags);
+
+		if (!(old_flags & BIT(PG_workingset))) {
+			new_flags = old_flags | BIT(PG_workingset);
+			continue;
+		}
+
+		usage = (old_flags & LRU_USAGE_MASK) + BIT(LRU_USAGE_PGOFF);
+
+		new_flags = (old_flags & ~LRU_USAGE_MASK) | min(usage, LRU_USAGE_MASK);
+	} while (new_flags != old_flags &&
+		 cmpxchg(&page->flags, old_flags, new_flags) != old_flags);
+}
+
 #else /* CONFIG_LRU_GEN */
 
 static inline bool lru_gen_enabled(void)
@@ -262,6 +298,10 @@ static inline bool lru_gen_deletion(struct page *page, struct lruvec *lruvec)
 	return false;
 }
 
+static inline void page_inc_usage(struct page *page)
+{
+}
+
 #endif /* CONFIG_LRU_GEN */
 
 static __always_inline void add_page_to_lru_list(struct page *page,
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 144727041e78..30b1f15f5c6e 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -365,8 +365,8 @@ extern void deactivate_page(struct page *page);
 extern void mark_page_lazyfree(struct page *page);
 extern void swap_setup(void);
 
-extern void lru_cache_add_inactive_or_unevictable(struct page *page,
-						struct vm_area_struct *vma);
+extern void lru_cache_add_page_vma(struct page *page, struct vm_area_struct *vma,
+				   bool faulting);
 
 /* linux/mm/vmscan.c */
 extern unsigned long zone_reclaimable_pages(struct zone *zone);
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index 6addc9780319..4e93e5602723 100644
--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -184,7 +184,7 @@ static int __replace_page(struct vm_area_struct *vma, unsigned long addr,
 	if (new_page) {
 		get_page(new_page);
 		page_add_new_anon_rmap(new_page, vma, addr, false);
-		lru_cache_add_inactive_or_unevictable(new_page, vma);
+		lru_cache_add_page_vma(new_page, vma, false);
 	} else
 		/* no new page, just dec_mm_counter for old_page */
 		dec_mm_counter(mm, MM_ANONPAGES);
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 8ac9093e5a0d..681da4a3cf61 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -636,7 +636,7 @@ static vm_fault_t __do_huge_pmd_anonymous_page(struct vm_fault *vmf,
 		entry = mk_huge_pmd(page, vma->vm_page_prot);
 		entry = maybe_pmd_mkwrite(pmd_mkdirty(entry), vma);
 		page_add_new_anon_rmap(page, vma, haddr, true);
-		lru_cache_add_inactive_or_unevictable(page, vma);
+		lru_cache_add_page_vma(page, vma, true);
 		pgtable_trans_huge_deposit(vma->vm_mm, vmf->pmd, pgtable);
 		set_pmd_at(vma->vm_mm, haddr, vmf->pmd, entry);
 		update_mmu_cache_pmd(vma, vmf->address, vmf->pmd);
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 6c0185fdd815..09e5346c2754 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -1198,7 +1198,7 @@ static void collapse_huge_page(struct mm_struct *mm,
 	spin_lock(pmd_ptl);
 	BUG_ON(!pmd_none(*pmd));
 	page_add_new_anon_rmap(new_page, vma, address, true);
-	lru_cache_add_inactive_or_unevictable(new_page, vma);
+	lru_cache_add_page_vma(new_page, vma, true);
 	pgtable_trans_huge_deposit(mm, pmd, pgtable);
 	set_pmd_at(mm, address, pmd, _pmd);
 	update_mmu_cache_pmd(vma, address, pmd);
diff --git a/mm/memory.c b/mm/memory.c
index 730daa00952b..a76196885f92 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -839,7 +839,7 @@ copy_present_page(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma
 	copy_user_highpage(new_page, page, addr, src_vma);
 	__SetPageUptodate(new_page);
 	page_add_new_anon_rmap(new_page, dst_vma, addr, false);
-	lru_cache_add_inactive_or_unevictable(new_page, dst_vma);
+	lru_cache_add_page_vma(new_page, dst_vma, false);
 	rss[mm_counter(new_page)]++;
 
 	/* All done, just insert the new page copy in the child */
@@ -2950,7 +2950,7 @@ static vm_fault_t wp_page_copy(struct vm_fault *vmf)
 		 */
 		ptep_clear_flush_notify(vma, vmf->address, vmf->pte);
 		page_add_new_anon_rmap(new_page, vma, vmf->address, false);
-		lru_cache_add_inactive_or_unevictable(new_page, vma);
+		lru_cache_add_page_vma(new_page, vma, true);
 		/*
 		 * We call the notify macro here because, when using secondary
 		 * mmu page tables (such as kvm shadow page tables), we want the
@@ -3479,7 +3479,7 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 	/* ksm created a completely new copy */
 	if (unlikely(page != swapcache && swapcache)) {
 		page_add_new_anon_rmap(page, vma, vmf->address, false);
-		lru_cache_add_inactive_or_unevictable(page, vma);
+		lru_cache_add_page_vma(page, vma, true);
 	} else {
 		do_page_add_anon_rmap(page, vma, vmf->address, exclusive);
 	}
@@ -3625,7 +3625,7 @@ static vm_fault_t do_anonymous_page(struct vm_fault *vmf)
 
 	inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES);
 	page_add_new_anon_rmap(page, vma, vmf->address, false);
-	lru_cache_add_inactive_or_unevictable(page, vma);
+	lru_cache_add_page_vma(page, vma, true);
 setpte:
 	set_pte_at(vma->vm_mm, vmf->address, vmf->pte, entry);
 
@@ -3793,7 +3793,7 @@ void do_set_pte(struct vm_fault *vmf, struct page *page, unsigned long addr)
 	if (write && !(vma->vm_flags & VM_SHARED)) {
 		inc_mm_counter_fast(vma->vm_mm, MM_ANONPAGES);
 		page_add_new_anon_rmap(page, vma, addr, false);
-		lru_cache_add_inactive_or_unevictable(page, vma);
+		lru_cache_add_page_vma(page, vma, true);
 	} else {
 		inc_mm_counter_fast(vma->vm_mm, mm_counter_file(page));
 		page_add_file_rmap(page, false);
diff --git a/mm/migrate.c b/mm/migrate.c
index b234c3f3acb7..d3307c9eced4 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2967,7 +2967,7 @@ static void migrate_vma_insert_page(struct migrate_vma *migrate,
 	inc_mm_counter(mm, MM_ANONPAGES);
 	page_add_new_anon_rmap(page, vma, addr, false);
 	if (!is_zone_device_page(page))
-		lru_cache_add_inactive_or_unevictable(page, vma);
+		lru_cache_add_page_vma(page, vma, false);
 	get_page(page);
 
 	if (flush) {
diff --git a/mm/swap.c b/mm/swap.c
index dfb48cf9c2c9..96ce95eeb2c9 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -433,6 +433,8 @@ void mark_page_accessed(struct page *page)
 		 * this list is never rotated or maintained, so marking an
 		 * evictable page accessed has no effect.
 		 */
+	} else if (lru_gen_enabled()) {
+		page_inc_usage(page);
 	} else if (!PageActive(page)) {
 		/*
 		 * If the page is on the LRU, queue it for activation via
@@ -478,15 +480,14 @@ void lru_cache_add(struct page *page)
 EXPORT_SYMBOL(lru_cache_add);
 
 /**
- * lru_cache_add_inactive_or_unevictable
+ * lru_cache_add_page_vma
  * @page:  the page to be added to LRU
  * @vma:   vma in which page is mapped for determining reclaimability
  *
- * Place @page on the inactive or unevictable LRU list, depending on its
- * evictability.
+ * Place @page on an LRU list, depending on its evictability.
  */
-void lru_cache_add_inactive_or_unevictable(struct page *page,
-					 struct vm_area_struct *vma)
+void lru_cache_add_page_vma(struct page *page, struct vm_area_struct *vma,
+			    bool faulting)
 {
 	bool unevictable;
 
@@ -503,6 +504,11 @@ void lru_cache_add_inactive_or_unevictable(struct page *page,
 		__mod_zone_page_state(page_zone(page), NR_MLOCK, nr_pages);
 		count_vm_events(UNEVICTABLE_PGMLOCKED, nr_pages);
 	}
+
+	/* tell the multigenerational lru that the page is being faulted in */
+	if (lru_gen_enabled() && !unevictable && faulting)
+		SetPageActive(page);
+
 	lru_cache_add(page);
 }
 
@@ -529,7 +535,7 @@ void lru_cache_add_inactive_or_unevictable(struct page *page,
  */
 static void lru_deactivate_file_fn(struct page *page, struct lruvec *lruvec)
 {
-	bool active = PageActive(page);
+	bool active = PageActive(page) || lru_gen_enabled();
 	int nr_pages = thp_nr_pages(page);
 
 	if (PageUnevictable(page))
@@ -569,7 +575,7 @@ static void lru_deactivate_file_fn(struct page *page, struct lruvec *lruvec)
 
 static void lru_deactivate_fn(struct page *page, struct lruvec *lruvec)
 {
-	if (PageActive(page) && !PageUnevictable(page)) {
+	if (!PageUnevictable(page) && (PageActive(page) || lru_gen_enabled())) {
 		int nr_pages = thp_nr_pages(page);
 
 		del_page_from_lru_list(page, lruvec);
@@ -684,7 +690,7 @@ void deactivate_file_page(struct page *page)
  */
 void deactivate_page(struct page *page)
 {
-	if (PageLRU(page) && PageActive(page) && !PageUnevictable(page)) {
+	if (PageLRU(page) && !PageUnevictable(page) && (PageActive(page) || lru_gen_enabled())) {
 		struct pagevec *pvec;
 
 		local_lock(&lru_pvecs.lock);
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 3598b668f533..549e94318b2f 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1936,7 +1936,7 @@ static int unuse_pte(struct vm_area_struct *vma, pmd_t *pmd,
 		page_add_anon_rmap(page, vma, addr, false);
 	} else { /* ksm created a completely new copy */
 		page_add_new_anon_rmap(page, vma, addr, false);
-		lru_cache_add_inactive_or_unevictable(page, vma);
+		lru_cache_add_page_vma(page, vma, false);
 	}
 	swap_free(entry);
 out:
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index e14b3820c6a8..175d55b4f594 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -123,7 +123,7 @@ static int mcopy_atomic_pte(struct mm_struct *dst_mm,
 
 	inc_mm_counter(dst_mm, MM_ANONPAGES);
 	page_add_new_anon_rmap(page, dst_vma, dst_addr, false);
-	lru_cache_add_inactive_or_unevictable(page, dst_vma);
+	lru_cache_add_page_vma(page, dst_vma, true);
 
 	set_pte_at(dst_mm, dst_addr, dst_pte, _dst_pte);
 
diff --git a/mm/vmscan.c b/mm/vmscan.c
index f7bbfc0b1ebd..84d25079092e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1094,9 +1094,11 @@ static int __remove_mapping(struct address_space *mapping, struct page *page,
 
 	if (PageSwapCache(page)) {
 		swp_entry_t swap = { .val = page_private(page) };
-		mem_cgroup_swapout(page, swap);
+
+		/* get a shadow entry before page_memcg() is cleared */
 		if (reclaimed && !mapping_exiting(mapping))
 			shadow = workingset_eviction(page, target_memcg);
+		mem_cgroup_swapout(page, swap);
 		__delete_from_swap_cache(page, swap, shadow);
 		xa_unlock_irqrestore(&mapping->i_pages, flags);
 		put_swap_page(page, swap);
@@ -2780,6 +2782,93 @@ static bool __maybe_unused seq_is_valid(struct lruvec *lruvec)
 	       get_nr_gens(lruvec, 1) <= MAX_NR_GENS;
 }
 
+/******************************************************************************
+ *                          refault feedback loop
+ ******************************************************************************/
+
+/*
+ * A feedback loop modeled after the PID controller. Currently supports the
+ * proportional (P) and the integral (I) terms; the derivative (D) term can be
+ * added if necessary. The setpoint (SP) is the desired position; the process
+ * variable (PV) is the measured position. The error is the difference between
+ * the SP and the PV. A positive error results in a positive control output
+ * correction, which, in our case, is to allow eviction.
+ *
+ * The P term is the current refault rate refaulted/(evicted+activated), which
+ * has a weight of 1. The I term is the arithmetic mean of the last N refault
+ * rates, weighted by geometric series 1/2, 1/4, ..., 1/(1<<N).
+ *
+ * Our goal is to make sure upper tiers have similar refault rates as the base
+ * tier. That is we try to be fair to all tiers by maintaining similar refault
+ * rates across them.
+ */
+struct controller_pos {
+	unsigned long refaulted;
+	unsigned long total;
+	int gain;
+};
+
+static void read_controller_pos(struct controller_pos *pos, struct lruvec *lruvec,
+				int type, int tier, int gain)
+{
+	struct lrugen *lrugen = &lruvec->evictable;
+	int hist = hist_from_seq_or_gen(lrugen->min_seq[type]);
+
+	pos->refaulted = lrugen->avg_refaulted[type][tier] +
+			 atomic_long_read(&lrugen->refaulted[hist][type][tier]);
+	pos->total = lrugen->avg_total[type][tier] +
+		     atomic_long_read(&lrugen->evicted[hist][type][tier]);
+	if (tier)
+		pos->total += lrugen->activated[hist][type][tier - 1];
+	pos->gain = gain;
+}
+
+static void reset_controller_pos(struct lruvec *lruvec, int gen, int type)
+{
+	int tier;
+	int hist = hist_from_seq_or_gen(gen);
+	struct lrugen *lrugen = &lruvec->evictable;
+	bool carryover = gen == lru_gen_from_seq(lrugen->min_seq[type]);
+
+	if (!carryover && NR_STAT_GENS == 1)
+		return;
+
+	for (tier = 0; tier < MAX_NR_TIERS; tier++) {
+		if (carryover) {
+			unsigned long sum;
+
+			sum = lrugen->avg_refaulted[type][tier] +
+			      atomic_long_read(&lrugen->refaulted[hist][type][tier]);
+			WRITE_ONCE(lrugen->avg_refaulted[type][tier], sum / 2);
+
+			sum = lrugen->avg_total[type][tier] +
+			      atomic_long_read(&lrugen->evicted[hist][type][tier]);
+			if (tier)
+				sum += lrugen->activated[hist][type][tier - 1];
+			WRITE_ONCE(lrugen->avg_total[type][tier], sum / 2);
+
+			if (NR_STAT_GENS > 1)
+				continue;
+		}
+
+		atomic_long_set(&lrugen->refaulted[hist][type][tier], 0);
+		atomic_long_set(&lrugen->evicted[hist][type][tier], 0);
+		if (tier)
+			WRITE_ONCE(lrugen->activated[hist][type][tier - 1], 0);
+	}
+}
+
+static bool positive_ctrl_err(struct controller_pos *sp, struct controller_pos *pv)
+{
+	/*
+	 * Allow eviction if the PV has a limited number of refaulted pages or a
+	 * lower refault rate than the SP.
+	 */
+	return pv->refaulted < SWAP_CLUSTER_MAX ||
+	       pv->refaulted * max(sp->total, 1UL) * sp->gain <=
+	       sp->refaulted * max(pv->total, 1UL) * pv->gain;
+}
+
 /******************************************************************************
  *                          state change
  ******************************************************************************/
diff --git a/mm/workingset.c b/mm/workingset.c
index edb8aed2587e..3f3f03d51ea7 100644
--- a/mm/workingset.c
+++ b/mm/workingset.c
@@ -201,6 +201,110 @@ static unsigned long unpack_shadow(void *shadow, int *memcg_id, struct pglist_da
 	return val >> MEM_CGROUP_ID_SHIFT;
 }
 
+#ifdef CONFIG_LRU_GEN
+
+#if LRU_GEN_SHIFT + LRU_USAGE_SHIFT >= EVICTION_SHIFT
+#error "Please try smaller NODES_SHIFT, NR_LRU_GENS and TIERS_PER_GEN configurations"
+#endif
+
+static void page_set_usage(struct page *page, int usage)
+{
+	unsigned long old_flags, new_flags;
+
+	VM_BUG_ON(usage > BIT(LRU_USAGE_WIDTH));
+
+	if (!usage)
+		return;
+
+	do {
+		old_flags = READ_ONCE(page->flags);
+		new_flags = (old_flags & ~LRU_USAGE_MASK) | LRU_TIER_FLAGS |
+			    ((usage - 1UL) << LRU_USAGE_PGOFF);
+	} while (new_flags != old_flags &&
+		 cmpxchg(&page->flags, old_flags, new_flags) != old_flags);
+}
+
+/* Return a token to be stored in the shadow entry of a page being evicted. */
+static void *lru_gen_eviction(struct page *page)
+{
+	int hist, tier;
+	unsigned long token;
+	unsigned long min_seq;
+	struct lruvec *lruvec;
+	struct lrugen *lrugen;
+	int type = page_is_file_lru(page);
+	int usage = page_tier_usage(page);
+	struct mem_cgroup *memcg = page_memcg(page);
+	struct pglist_data *pgdat = page_pgdat(page);
+
+	lruvec = mem_cgroup_lruvec(memcg, pgdat);
+	lrugen = &lruvec->evictable;
+	min_seq = READ_ONCE(lrugen->min_seq[type]);
+	token = (min_seq << LRU_USAGE_SHIFT) | usage;
+
+	hist = hist_from_seq_or_gen(min_seq);
+	tier = lru_tier_from_usage(usage);
+	atomic_long_add(thp_nr_pages(page), &lrugen->evicted[hist][type][tier]);
+
+	return pack_shadow(mem_cgroup_id(memcg), pgdat, token);
+}
+
+/* Account a refaulted page based on the token stored in its shadow entry. */
+static void lru_gen_refault(struct page *page, void *shadow)
+{
+	int hist, tier, usage;
+	int memcg_id;
+	unsigned long token;
+	unsigned long min_seq;
+	struct lruvec *lruvec;
+	struct lrugen *lrugen;
+	struct pglist_data *pgdat;
+	struct mem_cgroup *memcg;
+	int type = page_is_file_lru(page);
+
+	token = unpack_shadow(shadow, &memcg_id, &pgdat);
+	if (page_pgdat(page) != pgdat)
+		return;
+
+	rcu_read_lock();
+	memcg = page_memcg_rcu(page);
+	if (mem_cgroup_id(memcg) != memcg_id)
+		goto unlock;
+
+	usage = token & (BIT(LRU_USAGE_SHIFT) - 1);
+	token >>= LRU_USAGE_SHIFT;
+
+	lruvec = mem_cgroup_lruvec(memcg, pgdat);
+	lrugen = &lruvec->evictable;
+	min_seq = READ_ONCE(lrugen->min_seq[type]);
+	if (token != (min_seq & (EVICTION_MASK >> LRU_USAGE_SHIFT)))
+		goto unlock;
+
+	page_set_usage(page, usage);
+
+	hist = hist_from_seq_or_gen(min_seq);
+	tier = lru_tier_from_usage(usage);
+	atomic_long_add(thp_nr_pages(page), &lrugen->refaulted[hist][type][tier]);
+	inc_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + type);
+	if (tier)
+		inc_lruvec_state(lruvec, WORKINGSET_RESTORE_BASE + type);
+unlock:
+	rcu_read_unlock();
+}
+
+#else /* CONFIG_LRU_GEN */
+
+static void *lru_gen_eviction(struct page *page)
+{
+	return NULL;
+}
+
+static void lru_gen_refault(struct page *page, void *shadow)
+{
+}
+
+#endif /* CONFIG_LRU_GEN */
+
 /**
  * workingset_age_nonresident - age non-resident entries as LRU ages
  * @lruvec: the lruvec that was aged
@@ -249,6 +353,9 @@ void *workingset_eviction(struct page *page, struct mem_cgroup *target_memcg)
 	VM_BUG_ON_PAGE(page_count(page), page);
 	VM_BUG_ON_PAGE(!PageLocked(page), page);
 
+	if (lru_gen_enabled())
+		return lru_gen_eviction(page);
+
 	lruvec = mem_cgroup_lruvec(target_memcg, pgdat);
 	/* XXX: target_memcg can be NULL, go through lruvec */
 	memcgid = mem_cgroup_id(lruvec_memcg(lruvec));
@@ -283,6 +390,11 @@ void workingset_refault(struct page *page, void *shadow)
 	bool workingset;
 	int memcgid;
 
+	if (lru_gen_enabled()) {
+		lru_gen_refault(page, shadow);
+		return;
+	}
+
 	eviction = unpack_shadow(shadow, &memcgid, &pgdat);
 
 	rcu_read_lock();
-- 
2.31.1.751.gd2f1c929bd-goog

[PATCH v3 09/14] mm: multigenerational lru: mm_struct list

[Yu Zhao]

In order to scan page tables, we add an infrastructure to maintain
either a system-wide mm_struct list or per-memcg mm_struct lists, and
track whether an mm_struct is being used or has been used since the
last scan.

Multiple threads can concurrently work on the same mm_struct list, and
each of them will be given a different mm_struct belonging to a
process that has been scheduled since the last scan.

Signed-off-by: Yu Zhao <yuzhao@google.com>
Tested-by: Konstantin Kharlamov <Hi-Angel@yandex.ru>
---
 fs/exec.c                  |   2 +
 include/linux/memcontrol.h |   6 +
 include/linux/mm_types.h   | 107 ++++++++++++
 kernel/exit.c              |   1 +
 kernel/fork.c              |  10 ++
 kernel/kthread.c           |   1 +
 kernel/sched/core.c        |   2 +
 mm/memcontrol.c            |  28 ++++
 mm/vmscan.c                | 324 +++++++++++++++++++++++++++++++++++++
 9 files changed, 481 insertions(+)

diff --git a/fs/exec.c b/fs/exec.c
index 18594f11c31f..c691d4d7720c 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -1008,6 +1008,7 @@ static int exec_mmap(struct mm_struct *mm)
 	active_mm = tsk->active_mm;
 	tsk->active_mm = mm;
 	tsk->mm = mm;
+	lru_gen_add_mm(mm);
 	/*
 	 * This prevents preemption while active_mm is being loaded and
 	 * it and mm are being updated, which could cause problems for
@@ -1018,6 +1019,7 @@ static int exec_mmap(struct mm_struct *mm)
 	if (!IS_ENABLED(CONFIG_ARCH_WANT_IRQS_OFF_ACTIVATE_MM))
 		local_irq_enable();
 	activate_mm(active_mm, mm);
+	lru_gen_switch_mm(active_mm, mm);
 	if (IS_ENABLED(CONFIG_ARCH_WANT_IRQS_OFF_ACTIVATE_MM))
 		local_irq_enable();
 	tsk->mm->vmacache_seqnum = 0;
diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 6bcac3d91dd1..60601a997433 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -230,6 +230,8 @@ struct obj_cgroup {
 	};
 };
 
+struct lru_gen_mm_list;
+
 /*
  * The memory controller data structure. The memory controller controls both
  * page cache and RSS per cgroup. We would eventually like to provide
@@ -349,6 +351,10 @@ struct mem_cgroup {
 	struct deferred_split deferred_split_queue;
 #endif
 
+#ifdef CONFIG_LRU_GEN
+	struct lru_gen_mm_list *mm_list;
+#endif
+
 	struct mem_cgroup_per_node *nodeinfo[0];
 	/* WARNING: nodeinfo must be the last member here */
 };
diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 5aacc1c10a45..b0f662555eae 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -15,6 +15,8 @@
 #include <linux/page-flags-layout.h>
 #include <linux/workqueue.h>
 #include <linux/seqlock.h>
+#include <linux/nodemask.h>
+#include <linux/mmdebug.h>
 
 #include <asm/mmu.h>
 
@@ -561,6 +563,22 @@ struct mm_struct {
 
 #ifdef CONFIG_IOMMU_SUPPORT
 		u32 pasid;
+#endif
+#ifdef CONFIG_LRU_GEN
+		struct {
+			/* the node of a global or per-memcg mm_struct list */
+			struct list_head list;
+#ifdef CONFIG_MEMCG
+			/* points to the memcg of the owner task above */
+			struct mem_cgroup *memcg;
+#endif
+			/* whether this mm_struct has been used since the last walk */
+			nodemask_t nodes;
+#ifndef CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
+			/* the number of CPUs using this mm_struct */
+			atomic_t nr_cpus;
+#endif
+		} lrugen;
 #endif
 	} __randomize_layout;
 
@@ -588,6 +606,95 @@ static inline cpumask_t *mm_cpumask(struct mm_struct *mm)
 	return (struct cpumask *)&mm->cpu_bitmap;
 }
 
+#ifdef CONFIG_LRU_GEN
+
+void lru_gen_init_mm(struct mm_struct *mm);
+void lru_gen_add_mm(struct mm_struct *mm);
+void lru_gen_del_mm(struct mm_struct *mm);
+#ifdef CONFIG_MEMCG
+int lru_gen_alloc_mm_list(struct mem_cgroup *memcg);
+void lru_gen_free_mm_list(struct mem_cgroup *memcg);
+void lru_gen_migrate_mm(struct mm_struct *mm);
+#endif
+
+/* Track the usage of each mm_struct so that we can skip inactive ones. */
+static inline void lru_gen_switch_mm(struct mm_struct *old, struct mm_struct *new)
+{
+	/* exclude init_mm, efi_mm, etc. */
+	if (!core_kernel_data((unsigned long)old)) {
+		VM_BUG_ON(old == &init_mm);
+
+		nodes_setall(old->lrugen.nodes);
+#ifndef CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
+		atomic_dec(&old->lrugen.nr_cpus);
+		VM_BUG_ON_MM(atomic_read(&old->lrugen.nr_cpus) < 0, old);
+#endif
+	} else
+		VM_BUG_ON_MM(READ_ONCE(old->lrugen.list.prev) ||
+			     READ_ONCE(old->lrugen.list.next), old);
+
+	if (!core_kernel_data((unsigned long)new)) {
+		VM_BUG_ON(new == &init_mm);
+
+#ifndef CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
+		atomic_inc(&new->lrugen.nr_cpus);
+		VM_BUG_ON_MM(atomic_read(&new->lrugen.nr_cpus) < 0, new);
+#endif
+	} else
+		VM_BUG_ON_MM(READ_ONCE(new->lrugen.list.prev) ||
+			     READ_ONCE(new->lrugen.list.next), new);
+}
+
+/* Return whether this mm_struct is being used on any CPUs. */
+static inline bool lru_gen_mm_is_active(struct mm_struct *mm)
+{
+#ifdef CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
+	return !cpumask_empty(mm_cpumask(mm));
+#else
+	return atomic_read(&mm->lrugen.nr_cpus);
+#endif
+}
+
+#else /* CONFIG_LRU_GEN */
+
+static inline void lru_gen_init_mm(struct mm_struct *mm)
+{
+}
+
+static inline void lru_gen_add_mm(struct mm_struct *mm)
+{
+}
+
+static inline void lru_gen_del_mm(struct mm_struct *mm)
+{
+}
+
+#ifdef CONFIG_MEMCG
+static inline int lru_gen_alloc_mm_list(struct mem_cgroup *memcg)
+{
+	return 0;
+}
+
+static inline void lru_gen_free_mm_list(struct mem_cgroup *memcg)
+{
+}
+
+static inline void lru_gen_migrate_mm(struct mm_struct *mm)
+{
+}
+#endif
+
+static inline void lru_gen_switch_mm(struct mm_struct *old, struct mm_struct *new)
+{
+}
+
+static inline bool lru_gen_mm_is_active(struct mm_struct *mm)
+{
+	return false;
+}
+
+#endif /* CONFIG_LRU_GEN */
+
 struct mmu_gather;
 extern void tlb_gather_mmu(struct mmu_gather *tlb, struct mm_struct *mm);
 extern void tlb_gather_mmu_fullmm(struct mmu_gather *tlb, struct mm_struct *mm);
diff --git a/kernel/exit.c b/kernel/exit.c
index fd1c04193e18..b362179852f1 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -423,6 +423,7 @@ void mm_update_next_owner(struct mm_struct *mm)
 		goto retry;
 	}
 	WRITE_ONCE(mm->owner, c);
+	lru_gen_migrate_mm(mm);
 	task_unlock(c);
 	put_task_struct(c);
 }
diff --git a/kernel/fork.c b/kernel/fork.c
index dc06afd725cb..2fd7dae9afcb 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -669,6 +669,7 @@ static void check_mm(struct mm_struct *mm)
 #if defined(CONFIG_TRANSPARENT_HUGEPAGE) && !USE_SPLIT_PMD_PTLOCKS
 	VM_BUG_ON_MM(mm->pmd_huge_pte, mm);
 #endif
+	VM_BUG_ON_MM(lru_gen_mm_is_active(mm), mm);
 }
 
 #define allocate_mm()	(kmem_cache_alloc(mm_cachep, GFP_KERNEL))
@@ -1061,6 +1062,7 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p,
 		goto fail_nocontext;
 
 	mm->user_ns = get_user_ns(user_ns);
+	lru_gen_init_mm(mm);
 	return mm;
 
 fail_nocontext:
@@ -1103,6 +1105,7 @@ static inline void __mmput(struct mm_struct *mm)
 	}
 	if (mm->binfmt)
 		module_put(mm->binfmt->module);
+	lru_gen_del_mm(mm);
 	mmdrop(mm);
 }
 
@@ -2524,6 +2527,13 @@ pid_t kernel_clone(struct kernel_clone_args *args)
 		get_task_struct(p);
 	}
 
+	if (IS_ENABLED(CONFIG_LRU_GEN) && !(clone_flags & CLONE_VM)) {
+		/* lock the task to synchronize with memcg migration */
+		task_lock(p);
+		lru_gen_add_mm(p->mm);
+		task_unlock(p);
+	}
+
 	wake_up_new_task(p);
 
 	/* forking complete and child started to run, tell ptracer */
diff --git a/kernel/kthread.c b/kernel/kthread.c
index fe3f2a40d61e..b81e49ed31a7 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -1325,6 +1325,7 @@ void kthread_use_mm(struct mm_struct *mm)
 	tsk->mm = mm;
 	membarrier_update_current_mm(mm);
 	switch_mm_irqs_off(active_mm, mm, tsk);
+	lru_gen_switch_mm(active_mm, mm);
 	local_irq_enable();
 	task_unlock(tsk);
 #ifdef finish_arch_post_lock_switch
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 5226cc26a095..2d4b77f173db 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4323,6 +4323,7 @@ context_switch(struct rq *rq, struct task_struct *prev,
 		 * finish_task_switch()'s mmdrop().
 		 */
 		switch_mm_irqs_off(prev->active_mm, next->mm, next);
+		lru_gen_switch_mm(prev->active_mm, next->mm);
 
 		if (!prev->mm) {                        // from kernel
 			/* will mmdrop() in finish_task_switch(). */
@@ -7603,6 +7604,7 @@ void idle_task_exit(void)
 
 	if (mm != &init_mm) {
 		switch_mm(mm, &init_mm, current);
+		lru_gen_switch_mm(mm, &init_mm);
 		finish_arch_post_lock_switch();
 	}
 
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 64ada9e650a5..58b610ffa0e0 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4981,6 +4981,7 @@ static void __mem_cgroup_free(struct mem_cgroup *memcg)
 	for_each_node(node)
 		free_mem_cgroup_per_node_info(memcg, node);
 	free_percpu(memcg->vmstats_percpu);
+	lru_gen_free_mm_list(memcg);
 	kfree(memcg);
 }
 
@@ -5030,6 +5031,9 @@ static struct mem_cgroup *mem_cgroup_alloc(void)
 		if (alloc_mem_cgroup_per_node_info(memcg, node))
 			goto fail;
 
+	if (lru_gen_alloc_mm_list(memcg))
+		goto fail;
+
 	if (memcg_wb_domain_init(memcg, GFP_KERNEL))
 		goto fail;
 
@@ -5991,6 +5995,29 @@ static void mem_cgroup_move_task(void)
 }
 #endif
 
+#ifdef CONFIG_LRU_GEN
+static void mem_cgroup_attach(struct cgroup_taskset *tset)
+{
+	struct cgroup_subsys_state *css;
+	struct task_struct *task = NULL;
+
+	cgroup_taskset_for_each_leader(task, css, tset)
+		;
+
+	if (!task)
+		return;
+
+	task_lock(task);
+	if (task->mm && task->mm->owner == task)
+		lru_gen_migrate_mm(task->mm);
+	task_unlock(task);
+}
+#else
+static void mem_cgroup_attach(struct cgroup_taskset *tset)
+{
+}
+#endif
+
 static int seq_puts_memcg_tunable(struct seq_file *m, unsigned long value)
 {
 	if (value == PAGE_COUNTER_MAX)
@@ -6332,6 +6359,7 @@ struct cgroup_subsys memory_cgrp_subsys = {
 	.css_reset = mem_cgroup_css_reset,
 	.css_rstat_flush = mem_cgroup_css_rstat_flush,
 	.can_attach = mem_cgroup_can_attach,
+	.attach = mem_cgroup_attach,
 	.cancel_attach = mem_cgroup_cancel_attach,
 	.post_attach = mem_cgroup_move_task,
 	.dfl_cftypes = memory_files,
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 84d25079092e..d93d2272e475 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2869,6 +2869,323 @@ static bool positive_ctrl_err(struct controller_pos *sp, struct controller_pos *
 	       sp->refaulted * max(pv->total, 1UL) * pv->gain;
 }
 
+/******************************************************************************
+ *                          mm_struct list
+ ******************************************************************************/
+
+enum {
+	MM_SCHED_ACTIVE,	/* running processes */
+	MM_SCHED_INACTIVE,	/* sleeping processes */
+	MM_LOCK_CONTENTION,	/* lock contentions */
+	MM_VMA_INTERVAL,	/* VMAs within the range of each PUD/PMD/PTE */
+	MM_LEAF_OTHER_NODE,	/* entries not from the node under reclaim */
+	MM_LEAF_OTHER_MEMCG,	/* entries not from the memcg under reclaim */
+	MM_LEAF_OLD,		/* old entries */
+	MM_LEAF_YOUNG,		/* young entries */
+	MM_LEAF_DIRTY,		/* dirty entries */
+	MM_LEAF_HOLE,		/* non-present entries */
+	MM_NONLEAF_OLD,		/* old non-leaf PMD entries */
+	MM_NONLEAF_YOUNG,	/* young non-leaf PMD entries */
+	NR_MM_STATS
+};
+
+/* mnemonic codes for the stats above */
+#define MM_STAT_CODES		"aicvnmoydhlu"
+
+struct lru_gen_mm_list {
+	/* the head of a global or per-memcg mm_struct list */
+	struct list_head head;
+	/* protects the list */
+	spinlock_t lock;
+	struct {
+		/* set to max_seq after each round of walk */
+		unsigned long cur_seq;
+		/* the next mm on the list to walk */
+		struct list_head *iter;
+		/* to wait for the last worker to finish */
+		struct wait_queue_head wait;
+		/* the number of concurrent workers */
+		int nr_workers;
+		/* stats for debugging */
+		unsigned long stats[NR_STAT_GENS][NR_MM_STATS];
+	} nodes[0];
+};
+
+static struct lru_gen_mm_list *global_mm_list;
+
+static struct lru_gen_mm_list *alloc_mm_list(void)
+{
+	int nid;
+	struct lru_gen_mm_list *mm_list;
+
+	mm_list = kzalloc(struct_size(mm_list, nodes, nr_node_ids), GFP_KERNEL);
+	if (!mm_list)
+		return NULL;
+
+	INIT_LIST_HEAD(&mm_list->head);
+	spin_lock_init(&mm_list->lock);
+
+	for_each_node(nid) {
+		mm_list->nodes[nid].cur_seq = MIN_NR_GENS;
+		mm_list->nodes[nid].iter = &mm_list->head;
+		init_waitqueue_head(&mm_list->nodes[nid].wait);
+	}
+
+	return mm_list;
+}
+
+static struct lru_gen_mm_list *get_mm_list(struct mem_cgroup *memcg)
+{
+#ifdef CONFIG_MEMCG
+	if (!mem_cgroup_disabled())
+		return memcg ? memcg->mm_list : root_mem_cgroup->mm_list;
+#endif
+	VM_BUG_ON(memcg);
+
+	return global_mm_list;
+}
+
+void lru_gen_init_mm(struct mm_struct *mm)
+{
+	INIT_LIST_HEAD(&mm->lrugen.list);
+#ifdef CONFIG_MEMCG
+	mm->lrugen.memcg = NULL;
+#endif
+#ifndef CONFIG_ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
+	atomic_set(&mm->lrugen.nr_cpus, 0);
+#endif
+	nodes_clear(mm->lrugen.nodes);
+}
+
+void lru_gen_add_mm(struct mm_struct *mm)
+{
+	struct mem_cgroup *memcg = get_mem_cgroup_from_mm(mm);
+	struct lru_gen_mm_list *mm_list = get_mm_list(memcg);
+
+	VM_BUG_ON_MM(!list_empty(&mm->lrugen.list), mm);
+#ifdef CONFIG_MEMCG
+	VM_BUG_ON_MM(mm->lrugen.memcg, mm);
+	WRITE_ONCE(mm->lrugen.memcg, memcg);
+#endif
+	spin_lock(&mm_list->lock);
+	list_add_tail(&mm->lrugen.list, &mm_list->head);
+	spin_unlock(&mm_list->lock);
+}
+
+void lru_gen_del_mm(struct mm_struct *mm)
+{
+	int nid;
+#ifdef CONFIG_MEMCG
+	struct lru_gen_mm_list *mm_list = get_mm_list(mm->lrugen.memcg);
+#else
+	struct lru_gen_mm_list *mm_list = get_mm_list(NULL);
+#endif
+
+	spin_lock(&mm_list->lock);
+
+	for_each_node(nid) {
+		if (mm_list->nodes[nid].iter != &mm->lrugen.list)
+			continue;
+
+		mm_list->nodes[nid].iter = mm_list->nodes[nid].iter->next;
+		if (mm_list->nodes[nid].iter == &mm_list->head)
+			WRITE_ONCE(mm_list->nodes[nid].cur_seq,
+				   mm_list->nodes[nid].cur_seq + 1);
+	}
+
+	list_del_init(&mm->lrugen.list);
+
+	spin_unlock(&mm_list->lock);
+
+#ifdef CONFIG_MEMCG
+	mem_cgroup_put(mm->lrugen.memcg);
+	WRITE_ONCE(mm->lrugen.memcg, NULL);
+#endif
+}
+
+#ifdef CONFIG_MEMCG
+int lru_gen_alloc_mm_list(struct mem_cgroup *memcg)
+{
+	if (mem_cgroup_disabled())
+		return 0;
+
+	memcg->mm_list = alloc_mm_list();
+
+	return memcg->mm_list ? 0 : -ENOMEM;
+}
+
+void lru_gen_free_mm_list(struct mem_cgroup *memcg)
+{
+	kfree(memcg->mm_list);
+	memcg->mm_list = NULL;
+}
+
+void lru_gen_migrate_mm(struct mm_struct *mm)
+{
+	struct mem_cgroup *memcg;
+
+	lockdep_assert_held(&mm->owner->alloc_lock);
+
+	if (mem_cgroup_disabled())
+		return;
+
+	rcu_read_lock();
+	memcg = mem_cgroup_from_task(mm->owner);
+	rcu_read_unlock();
+	if (memcg == mm->lrugen.memcg)
+		return;
+
+	VM_BUG_ON_MM(!mm->lrugen.memcg, mm);
+	VM_BUG_ON_MM(list_empty(&mm->lrugen.list), mm);
+
+	lru_gen_del_mm(mm);
+	lru_gen_add_mm(mm);
+}
+
+static bool mm_has_migrated(struct mm_struct *mm, struct mem_cgroup *memcg)
+{
+	return READ_ONCE(mm->lrugen.memcg) != memcg;
+}
+#else
+static bool mm_has_migrated(struct mm_struct *mm, struct mem_cgroup *memcg)
+{
+	return false;
+}
+#endif
+
+struct mm_walk_args {
+	struct mem_cgroup *memcg;
+	unsigned long max_seq;
+	unsigned long start_pfn;
+	unsigned long end_pfn;
+	unsigned long next_addr;
+	int node_id;
+	int swappiness;
+	int batch_size;
+	int nr_pages[MAX_NR_GENS][ANON_AND_FILE][MAX_NR_ZONES];
+	int mm_stats[NR_MM_STATS];
+	unsigned long bitmap[0];
+};
+
+static int size_of_mm_walk_args(void)
+{
+	int size = sizeof(struct mm_walk_args);
+
+	if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) ||
+	    IS_ENABLED(CONFIG_HAVE_ARCH_PARENT_PMD_YOUNG))
+		size += sizeof(unsigned long) * BITS_TO_LONGS(PTRS_PER_PMD);
+
+	return size;
+}
+
+static void reset_mm_stats(struct lru_gen_mm_list *mm_list, bool last,
+			   struct mm_walk_args *args)
+{
+	int i;
+	int nid = args->node_id;
+	int hist = hist_from_seq_or_gen(args->max_seq);
+
+	lockdep_assert_held(&mm_list->lock);
+
+	for (i = 0; i < NR_MM_STATS; i++) {
+		WRITE_ONCE(mm_list->nodes[nid].stats[hist][i],
+			   mm_list->nodes[nid].stats[hist][i] + args->mm_stats[i]);
+		args->mm_stats[i] = 0;
+	}
+
+	if (!last || NR_STAT_GENS == 1)
+		return;
+
+	hist = hist_from_seq_or_gen(args->max_seq + 1);
+	for (i = 0; i < NR_MM_STATS; i++)
+		WRITE_ONCE(mm_list->nodes[nid].stats[hist][i], 0);
+}
+
+static bool should_skip_mm(struct mm_struct *mm, struct mm_walk_args *args)
+{
+	int type;
+	unsigned long size = 0;
+
+	if (!lru_gen_mm_is_active(mm) && !node_isset(args->node_id, mm->lrugen.nodes))
+		return true;
+
+	if (mm_is_oom_victim(mm))
+		return true;
+
+	for (type = !args->swappiness; type < ANON_AND_FILE; type++) {
+		size += type ? get_mm_counter(mm, MM_FILEPAGES) :
+			       get_mm_counter(mm, MM_ANONPAGES) +
+			       get_mm_counter(mm, MM_SHMEMPAGES);
+	}
+
+	/* leave the legwork to the rmap if mappings are too sparse */
+	if (size < max(SWAP_CLUSTER_MAX, mm_pgtables_bytes(mm) / PAGE_SIZE))
+		return true;
+
+	return !mmget_not_zero(mm);
+}
+
+/* To support multiple workers that concurrently walk an mm_struct list. */
+static bool get_next_mm(struct mm_walk_args *args, struct mm_struct **iter)
+{
+	bool last = true;
+	struct mm_struct *mm = NULL;
+	int nid = args->node_id;
+	struct lru_gen_mm_list *mm_list = get_mm_list(args->memcg);
+
+	if (*iter)
+		mmput_async(*iter);
+	else if (args->max_seq <= READ_ONCE(mm_list->nodes[nid].cur_seq))
+		return false;
+
+	spin_lock(&mm_list->lock);
+
+	VM_BUG_ON(args->max_seq > mm_list->nodes[nid].cur_seq + 1);
+	VM_BUG_ON(*iter && args->max_seq < mm_list->nodes[nid].cur_seq);
+	VM_BUG_ON(*iter && !mm_list->nodes[nid].nr_workers);
+
+	if (args->max_seq <= mm_list->nodes[nid].cur_seq) {
+		last = *iter;
+		goto done;
+	}
+
+	if (mm_list->nodes[nid].iter == &mm_list->head) {
+		VM_BUG_ON(*iter || mm_list->nodes[nid].nr_workers);
+		mm_list->nodes[nid].iter = mm_list->nodes[nid].iter->next;
+	}
+
+	while (!mm && mm_list->nodes[nid].iter != &mm_list->head) {
+		mm = list_entry(mm_list->nodes[nid].iter, struct mm_struct, lrugen.list);
+		mm_list->nodes[nid].iter = mm_list->nodes[nid].iter->next;
+		if (should_skip_mm(mm, args))
+			mm = NULL;
+
+		args->mm_stats[mm ? MM_SCHED_ACTIVE : MM_SCHED_INACTIVE]++;
+	}
+
+	if (mm_list->nodes[nid].iter == &mm_list->head)
+		WRITE_ONCE(mm_list->nodes[nid].cur_seq,
+			   mm_list->nodes[nid].cur_seq + 1);
+done:
+	if (*iter && !mm)
+		mm_list->nodes[nid].nr_workers--;
+	if (!*iter && mm)
+		mm_list->nodes[nid].nr_workers++;
+
+	last = last && !mm_list->nodes[nid].nr_workers &&
+	       mm_list->nodes[nid].iter == &mm_list->head;
+
+	reset_mm_stats(mm_list, last, args);
+
+	spin_unlock(&mm_list->lock);
+
+	*iter = mm;
+	if (mm)
+		node_clear(nid, mm->lrugen.nodes);
+
+	return last;
+}
+
 /******************************************************************************
  *                          state change
  ******************************************************************************/
@@ -3096,6 +3413,13 @@ 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);
+	BUILD_BUG_ON(sizeof(MM_STAT_CODES) != NR_MM_STATS + 1);
+
+	if (mem_cgroup_disabled()) {
+		global_mm_list = alloc_mm_list();
+		if (WARN_ON_ONCE(!global_mm_list))
+			return -ENOMEM;
+	}
 
 	if (hotplug_memory_notifier(lru_gen_online_mem, 0))
 		pr_err("lru_gen: failed to subscribe hotplug notifications\n");
-- 
2.31.1.751.gd2f1c929bd-goog

[PATCH v3 10/14] mm: multigenerational lru: aging

[Yu Zhao]

The aging produces young generations. Given an lruvec, the aging scans
page tables for referenced pages of this lruvec. Upon finding one, the
aging updates its generation number to max_seq. After each round of
scan, the aging increments max_seq. The aging is due when both of
min_seq[2] reaches max_seq-1, assuming both anon and file types are
reclaimable.

The aging uses the following optimizations when scanning page tables:
  1) It will not scan page tables from processes that have been
  sleeping since the last scan.
  2) It will not scan PTE tables under non-leaf PMD entries that do
  not have the accessed bit set, when
  CONFIG_HAVE_ARCH_PARENT_PMD_YOUNG=y.
  3) It will not zigzag between the PGD table and the same PMD or PTE
  table spanning multiple VMAs. In other words, it finishes all the
  VMAs within the range of the same PMD or PTE table before it returns
  to the PGD table. This optimizes workloads that have large numbers
  of tiny VMAs, especially when CONFIG_PGTABLE_LEVELS=5.

The aging also takes advantage of the spatial locality: pages mapped
around a referenced PTE may also have been referenced. If the rmap
finds the PTE mapping a page under reclaim referenced, it will call a
new function lru_gen_scan_around() to scan the vicinity of this PTE.
And for each additional PTE found referenced, lru_gen_scan_around()
will update the generation number of the page mapped by this PTE.

Signed-off-by: Yu Zhao <yuzhao@google.com>
Tested-by: Konstantin Kharlamov <Hi-Angel@yandex.ru>
---
 include/linux/mmzone.h |   6 +
 mm/rmap.c              |   6 +
 mm/vmscan.c            | 788 +++++++++++++++++++++++++++++++++++++++++
 3 files changed, 800 insertions(+)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index e5deec17b4bd..38de59fcbe54 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -294,6 +294,7 @@ enum lruvec_flags {
 };
 
 struct lruvec;
+struct page_vma_mapped_walk;
 
 #define LRU_GEN_MASK		((BIT(LRU_GEN_WIDTH) - 1) << LRU_GEN_PGOFF)
 #define LRU_USAGE_MASK		((BIT(LRU_USAGE_WIDTH) - 1) << LRU_USAGE_PGOFF)
@@ -382,6 +383,7 @@ struct lrugen {
 
 void lru_gen_init_lruvec(struct lruvec *lruvec);
 void lru_gen_set_state(bool enable, bool main, bool swap);
+void lru_gen_scan_around(struct page_vma_mapped_walk *pvmw);
 
 #else /* CONFIG_LRU_GEN */
 
@@ -393,6 +395,10 @@ static inline void lru_gen_set_state(bool enable, bool main, bool swap)
 {
 }
 
+static inline void lru_gen_scan_around(struct page_vma_mapped_walk *pvmw)
+{
+}
+
 #endif /* CONFIG_LRU_GEN */
 
 struct lruvec {
diff --git a/mm/rmap.c b/mm/rmap.c
index 693a610e181d..985cf4ebd03c 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -72,6 +72,7 @@
 #include <linux/page_idle.h>
 #include <linux/memremap.h>
 #include <linux/userfaultfd_k.h>
+#include <linux/mm_inline.h>
 
 #include <asm/tlbflush.h>
 
@@ -792,6 +793,11 @@ static bool page_referenced_one(struct page *page, struct vm_area_struct *vma,
 		}
 
 		if (pvmw.pte) {
+			/* the multigenerational lru exploits the spatial locality */
+			if (lru_gen_enabled() && pte_young(*pvmw.pte)) {
+				lru_gen_scan_around(&pvmw);
+				referenced++;
+			}
 			if (ptep_clear_flush_young_notify(vma, address,
 						pvmw.pte)) {
 				/*
diff --git a/mm/vmscan.c b/mm/vmscan.c
index d93d2272e475..837d5e6a821e 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -50,6 +50,8 @@
 #include <linux/dax.h>
 #include <linux/psi.h>
 #include <linux/memory.h>
+#include <linux/pagewalk.h>
+#include <linux/shmem_fs.h>
 
 #include <asm/tlbflush.h>
 #include <asm/div64.h>
@@ -3186,6 +3188,788 @@ static bool get_next_mm(struct mm_walk_args *args, struct mm_struct **iter)
 	return last;
 }
 
+/******************************************************************************
+ *                          the aging
+ ******************************************************************************/
+
+static void update_batch_size(struct page *page, int old_gen, int new_gen,
+			      struct mm_walk_args *args)
+{
+	int type = page_is_file_lru(page);
+	int zone = page_zonenum(page);
+	int delta = thp_nr_pages(page);
+
+	VM_BUG_ON(old_gen >= MAX_NR_GENS);
+	VM_BUG_ON(new_gen >= MAX_NR_GENS);
+
+	args->batch_size++;
+
+	args->nr_pages[old_gen][type][zone] -= delta;
+	args->nr_pages[new_gen][type][zone] += delta;
+}
+
+static void reset_batch_size(struct lruvec *lruvec, struct mm_walk_args *args)
+{
+	int gen, type, zone;
+	struct lrugen *lrugen = &lruvec->evictable;
+
+	if (!args->batch_size)
+		return;
+
+	args->batch_size = 0;
+
+	spin_lock_irq(&lruvec->lru_lock);
+
+	for_each_gen_type_zone(gen, type, zone) {
+		enum lru_list lru = type * LRU_FILE;
+		int total = args->nr_pages[gen][type][zone];
+
+		if (!total)
+			continue;
+
+		args->nr_pages[gen][type][zone] = 0;
+		WRITE_ONCE(lrugen->sizes[gen][type][zone],
+			   lrugen->sizes[gen][type][zone] + total);
+
+		if (lru_gen_is_active(lruvec, gen))
+			lru += LRU_ACTIVE;
+		update_lru_size(lruvec, lru, zone, total);
+	}
+
+	spin_unlock_irq(&lruvec->lru_lock);
+}
+
+static int page_update_gen(struct page *page, int new_gen)
+{
+	int old_gen;
+	unsigned long old_flags, new_flags;
+
+	VM_BUG_ON(new_gen >= MAX_NR_GENS);
+
+	do {
+		old_flags = READ_ONCE(page->flags);
+
+		old_gen = ((old_flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1;
+		if (old_gen < 0) {
+			new_flags = old_flags | BIT(PG_referenced);
+			continue;
+		}
+
+		new_flags = (old_flags & ~(LRU_GEN_MASK | LRU_USAGE_MASK | LRU_TIER_FLAGS)) |
+			    ((new_gen + 1UL) << LRU_GEN_PGOFF);
+	} while (new_flags != old_flags &&
+		 cmpxchg(&page->flags, old_flags, new_flags) != old_flags);
+
+	return old_gen;
+}
+
+static int should_skip_vma(unsigned long start, unsigned long end, struct mm_walk *walk)
+{
+	struct address_space *mapping;
+	struct vm_area_struct *vma = walk->vma;
+	struct mm_walk_args *args = walk->private;
+
+	if (!vma_is_accessible(vma) || is_vm_hugetlb_page(vma) ||
+	    (vma->vm_flags & (VM_LOCKED | VM_SPECIAL)))
+		return true;
+
+	if (vma_is_anonymous(vma))
+		return !args->swappiness;
+
+	if (WARN_ON_ONCE(!vma->vm_file || !vma->vm_file->f_mapping))
+		return true;
+
+	mapping = vma->vm_file->f_mapping;
+	if (!mapping->a_ops->writepage)
+		return true;
+
+	return (shmem_mapping(mapping) && !args->swappiness) || mapping_unevictable(mapping);
+}
+
+/*
+ * Some userspace memory allocators create many single-page VMAs. So instead of
+ * returning back to the PGD table for each of such VMAs, we finish at least an
+ * entire PMD table and therefore avoid many zigzags. This optimizes page table
+ * walks for workloads that have large numbers of tiny VMAs.
+ *
+ * We scan PMD tables in two passes. The first pass reaches to PTE tables and
+ * doesn't take the PMD lock. The second pass clears the accessed bit on PMD
+ * entries and needs to take the PMD lock. The second pass is only done on the
+ * PMD entries that first pass has found the accessed bit is set, namely
+ *   1) leaf entries mapping huge pages from the node under reclaim, and
+ *   2) non-leaf entries whose leaf entries only map pages from the node under
+ *   reclaim, when CONFIG_HAVE_ARCH_PARENT_PMD_YOUNG=y.
+ */
+static bool get_next_vma(struct mm_walk *walk, unsigned long mask, unsigned long size,
+			 unsigned long *start, unsigned long *end)
+{
+	unsigned long next = round_up(*end, size);
+	struct mm_walk_args *args = walk->private;
+
+	VM_BUG_ON(mask & size);
+	VM_BUG_ON(*start >= *end);
+	VM_BUG_ON((next & mask) != (*start & mask));
+
+	while (walk->vma) {
+		if (next >= walk->vma->vm_end) {
+			walk->vma = walk->vma->vm_next;
+			continue;
+		}
+
+		if ((next & mask) != (walk->vma->vm_start & mask))
+			return false;
+
+		if (should_skip_vma(walk->vma->vm_start, walk->vma->vm_end, walk)) {
+			walk->vma = walk->vma->vm_next;
+			continue;
+		}
+
+		*start = max(next, walk->vma->vm_start);
+		next = (next | ~mask) + 1;
+		/* rounded-up boundaries can wrap to 0 */
+		*end = next && next < walk->vma->vm_end ? next : walk->vma->vm_end;
+
+		args->mm_stats[MM_VMA_INTERVAL]++;
+
+		return true;
+	}
+
+	return false;
+}
+
+static bool walk_pte_range(pmd_t *pmd, unsigned long start, unsigned long end,
+			   struct mm_walk *walk)
+{
+	int i;
+	pte_t *pte;
+	spinlock_t *ptl;
+	unsigned long addr;
+	int remote = 0;
+	struct mm_walk_args *args = walk->private;
+	int old_gen, new_gen = lru_gen_from_seq(args->max_seq);
+
+	VM_BUG_ON(pmd_leaf(*pmd));
+
+	pte = pte_offset_map_lock(walk->mm, pmd, start & PMD_MASK, &ptl);
+	arch_enter_lazy_mmu_mode();
+restart:
+	for (i = pte_index(start), addr = start; addr != end; i++, addr += PAGE_SIZE) {
+		struct page *page;
+		unsigned long pfn = pte_pfn(pte[i]);
+
+		if (!pte_present(pte[i]) || is_zero_pfn(pfn)) {
+			args->mm_stats[MM_LEAF_HOLE]++;
+			continue;
+		}
+
+		if (WARN_ON_ONCE(pte_devmap(pte[i]) || pte_special(pte[i])))
+			continue;
+
+		if (!pte_young(pte[i])) {
+			args->mm_stats[MM_LEAF_OLD]++;
+			continue;
+		}
+
+		VM_BUG_ON(!pfn_valid(pfn));
+		if (pfn < args->start_pfn || pfn >= args->end_pfn) {
+			args->mm_stats[MM_LEAF_OTHER_NODE]++;
+			remote++;
+			continue;
+		}
+
+		page = compound_head(pfn_to_page(pfn));
+		if (page_to_nid(page) != args->node_id) {
+			args->mm_stats[MM_LEAF_OTHER_NODE]++;
+			remote++;
+			continue;
+		}
+
+		if (page_memcg_rcu(page) != args->memcg) {
+			args->mm_stats[MM_LEAF_OTHER_MEMCG]++;
+			continue;
+		}
+
+		VM_BUG_ON(addr < walk->vma->vm_start || addr >= walk->vma->vm_end);
+		if (!ptep_test_and_clear_young(walk->vma, addr, pte + i))
+			continue;
+
+		if (pte_dirty(pte[i]) && !PageDirty(page) &&
+		    !(PageAnon(page) && PageSwapBacked(page) && !PageSwapCache(page))) {
+			set_page_dirty(page);
+			args->mm_stats[MM_LEAF_DIRTY]++;
+		}
+
+		old_gen = page_update_gen(page, new_gen);
+		if (old_gen >= 0 && old_gen != new_gen)
+			update_batch_size(page, old_gen, new_gen, args);
+		args->mm_stats[MM_LEAF_YOUNG]++;
+	}
+
+	if (i < PTRS_PER_PTE && get_next_vma(walk, PMD_MASK, PAGE_SIZE, &start, &end))
+		goto restart;
+
+	arch_leave_lazy_mmu_mode();
+	pte_unmap_unlock(pte, ptl);
+
+	return IS_ENABLED(CONFIG_HAVE_ARCH_PARENT_PMD_YOUNG) && !remote;
+}
+
+#if defined(CONFIG_TRANSPARENT_HUGEPAGE) || defined(CONFIG_HAVE_ARCH_PARENT_PMD_YOUNG)
+static void __walk_pmd_range(pud_t *pud, unsigned long start,
+			     struct vm_area_struct *vma, struct mm_walk *walk)
+{
+	int i;
+	pmd_t *pmd;
+	spinlock_t *ptl;
+	struct mm_walk_args *args = walk->private;
+	int old_gen, new_gen = lru_gen_from_seq(args->max_seq);
+
+	VM_BUG_ON(pud_leaf(*pud));
+
+	start &= PUD_MASK;
+	pmd = pmd_offset(pud, start);
+	ptl = pmd_lock(walk->mm, pmd);
+	arch_enter_lazy_mmu_mode();
+
+	for_each_set_bit(i, args->bitmap, PTRS_PER_PMD) {
+		struct page *page;
+		unsigned long pfn = pmd_pfn(pmd[i]);
+		unsigned long addr = start + i * PMD_SIZE;
+
+		if (!pmd_present(pmd[i]) || is_huge_zero_pmd(pmd[i])) {
+			args->mm_stats[MM_LEAF_HOLE]++;
+			continue;
+		}
+
+		if (WARN_ON_ONCE(pmd_devmap(pmd[i])))
+			continue;
+
+		if (!pmd_young(pmd[i])) {
+			args->mm_stats[MM_LEAF_OLD]++;
+			continue;
+		}
+
+		if (!pmd_trans_huge(pmd[i])) {
+			if (IS_ENABLED(CONFIG_HAVE_ARCH_PARENT_PMD_YOUNG) &&
+			    pmdp_test_and_clear_young(vma, addr, pmd + i))
+				args->mm_stats[MM_NONLEAF_YOUNG]++;
+			continue;
+		}
+
+		VM_BUG_ON(!pfn_valid(pfn));
+		if (pfn < args->start_pfn || pfn >= args->end_pfn) {
+			args->mm_stats[MM_LEAF_OTHER_NODE]++;
+			continue;
+		}
+
+		page = pfn_to_page(pfn);
+		VM_BUG_ON_PAGE(PageTail(page), page);
+		if (page_to_nid(page) != args->node_id) {
+			args->mm_stats[MM_LEAF_OTHER_NODE]++;
+			continue;
+		}
+
+		if (page_memcg_rcu(page) != args->memcg) {
+			args->mm_stats[MM_LEAF_OTHER_MEMCG]++;
+			continue;
+		}
+
+		VM_BUG_ON(addr < vma->vm_start || addr >= vma->vm_end);
+		if (!pmdp_test_and_clear_young(vma, addr, pmd + i))
+			continue;
+
+		if (pmd_dirty(pmd[i]) && !PageDirty(page) &&
+		    !(PageAnon(page) && PageSwapBacked(page) && !PageSwapCache(page))) {
+			set_page_dirty(page);
+			args->mm_stats[MM_LEAF_DIRTY]++;
+		}
+
+		old_gen = page_update_gen(page, new_gen);
+		if (old_gen >= 0 && old_gen != new_gen)
+			update_batch_size(page, old_gen, new_gen, args);
+		args->mm_stats[MM_LEAF_YOUNG]++;
+	}
+
+	arch_leave_lazy_mmu_mode();
+	spin_unlock(ptl);
+
+	bitmap_zero(args->bitmap, PTRS_PER_PMD);
+}
+#else
+static void __walk_pmd_range(pud_t *pud, unsigned long start,
+			     struct vm_area_struct *vma, struct mm_walk *walk)
+{
+}
+#endif
+
+static void walk_pmd_range(pud_t *pud, unsigned long start, unsigned long end,
+			   struct mm_walk *walk)
+{
+	int i;
+	pmd_t *pmd;
+	unsigned long next;
+	unsigned long addr;
+	struct vm_area_struct *vma;
+	int leaf = 0;
+	int nonleaf = 0;
+	struct mm_walk_args *args = walk->private;
+
+	VM_BUG_ON(pud_leaf(*pud));
+
+	pmd = pmd_offset(pud, start & PUD_MASK);
+restart:
+	vma = walk->vma;
+	for (i = pmd_index(start), addr = start; addr != end; i++, addr = next) {
+		pmd_t val = pmd_read_atomic(pmd + i);
+
+		/* for pmd_read_atomic() */
+		barrier();
+
+		next = pmd_addr_end(addr, end);
+
+		if (!pmd_present(val)) {
+			args->mm_stats[MM_LEAF_HOLE]++;
+			continue;
+		}
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+		if (pmd_trans_huge(val)) {
+			unsigned long pfn = pmd_pfn(val);
+
+			if (is_huge_zero_pmd(val)) {
+				args->mm_stats[MM_LEAF_HOLE]++;
+				continue;
+			}
+
+			if (!pmd_young(val)) {
+				args->mm_stats[MM_LEAF_OLD]++;
+				continue;
+			}
+
+			if (pfn < args->start_pfn || pfn >= args->end_pfn) {
+				args->mm_stats[MM_LEAF_OTHER_NODE]++;
+				continue;
+			}
+
+			__set_bit(i, args->bitmap);
+			leaf++;
+			continue;
+		}
+#endif
+
+#ifdef CONFIG_HAVE_ARCH_PARENT_PMD_YOUNG
+		if (!pmd_young(val)) {
+			args->mm_stats[MM_NONLEAF_OLD]++;
+			continue;
+		}
+#endif
+		if (walk_pte_range(&val, addr, next, walk)) {
+			__set_bit(i, args->bitmap);
+			nonleaf++;
+		}
+	}
+
+	if (leaf) {
+		__walk_pmd_range(pud, start, vma, walk);
+		leaf = nonleaf = 0;
+	}
+
+	if (i < PTRS_PER_PMD && get_next_vma(walk, PUD_MASK, PMD_SIZE, &start, &end))
+		goto restart;
+
+	if (nonleaf)
+		__walk_pmd_range(pud, start, vma, walk);
+}
+
+static int walk_pud_range(p4d_t *p4d, unsigned long start, unsigned long end,
+			  struct mm_walk *walk)
+{
+	int i;
+	pud_t *pud;
+	unsigned long addr;
+	unsigned long next;
+	struct mm_walk_args *args = walk->private;
+
+	VM_BUG_ON(p4d_leaf(*p4d));
+
+	pud = pud_offset(p4d, start & P4D_MASK);
+restart:
+	for (i = pud_index(start), addr = start; addr != end; i++, addr = next) {
+		pud_t val = READ_ONCE(pud[i]);
+
+		next = pud_addr_end(addr, end);
+
+		if (!pud_present(val) || WARN_ON_ONCE(pud_leaf(val)))
+			continue;
+
+		walk_pmd_range(&val, addr, next, walk);
+
+		if (args->batch_size >= MAX_BATCH_SIZE) {
+			end = (addr | ~PUD_MASK) + 1;
+			goto done;
+		}
+	}
+
+	if (i < PTRS_PER_PUD && get_next_vma(walk, P4D_MASK, PUD_SIZE, &start, &end))
+		goto restart;
+
+	end = round_up(end, P4D_SIZE);
+done:
+	/* rounded-up boundaries can wrap to 0 */
+	args->next_addr = end && walk->vma ? max(end, walk->vma->vm_start) : 0;
+
+	return -EAGAIN;
+}
+
+static void walk_mm(struct mm_walk_args *args, struct mm_struct *mm)
+{
+	static const struct mm_walk_ops mm_walk_ops = {
+		.test_walk = should_skip_vma,
+		.p4d_entry = walk_pud_range,
+	};
+
+	int err;
+	struct mem_cgroup *memcg = args->memcg;
+	struct lruvec *lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(args->node_id));
+
+	args->next_addr = FIRST_USER_ADDRESS;
+
+	do {
+		unsigned long start = args->next_addr;
+		unsigned long end = mm->highest_vm_end;
+
+		err = -EBUSY;
+
+		preempt_disable();
+		rcu_read_lock();
+
+#ifdef CONFIG_MEMCG
+		if (memcg && atomic_read(&memcg->moving_account)) {
+			args->mm_stats[MM_LOCK_CONTENTION]++;
+			goto contended;
+		}
+#endif
+		if (!mmap_read_trylock(mm)) {
+			args->mm_stats[MM_LOCK_CONTENTION]++;
+			goto contended;
+		}
+
+		err = walk_page_range(mm, start, end, &mm_walk_ops, args);
+
+		mmap_read_unlock(mm);
+
+		reset_batch_size(lruvec, args);
+contended:
+		rcu_read_unlock();
+		preempt_enable();
+
+		cond_resched();
+	} while (err == -EAGAIN && args->next_addr &&
+		 !mm_is_oom_victim(mm) && !mm_has_migrated(mm, memcg));
+}
+
+static void page_inc_gen(struct page *page, struct lruvec *lruvec, bool front)
+{
+	int old_gen, new_gen;
+	unsigned long old_flags, new_flags;
+	int type = page_is_file_lru(page);
+	int zone = page_zonenum(page);
+	struct lrugen *lrugen = &lruvec->evictable;
+
+	old_gen = lru_gen_from_seq(lrugen->min_seq[type]);
+
+	do {
+		old_flags = READ_ONCE(page->flags);
+
+		/* in case the aging has updated old_gen */
+		new_gen = ((old_flags & LRU_GEN_MASK) >> LRU_GEN_PGOFF) - 1;
+		VM_BUG_ON_PAGE(new_gen < 0, page);
+		if (new_gen >= 0 && new_gen != old_gen)
+			goto sort;
+
+		new_gen = (old_gen + 1) % MAX_NR_GENS;
+
+		new_flags = (old_flags & ~(LRU_GEN_MASK | LRU_USAGE_MASK | LRU_TIER_FLAGS)) |
+			    ((new_gen + 1UL) << LRU_GEN_PGOFF);
+		/* mark the page for reclaim if it's pending writeback */
+		if (front)
+			new_flags |= BIT(PG_reclaim);
+	} while (cmpxchg(&page->flags, old_flags, new_flags) != old_flags);
+
+	lru_gen_update_size(page, lruvec, old_gen, new_gen);
+sort:
+	if (front)
+		list_move(&page->lru, &lrugen->lists[new_gen][type][zone]);
+	else
+		list_move_tail(&page->lru, &lrugen->lists[new_gen][type][zone]);
+}
+
+static bool try_inc_min_seq(struct lruvec *lruvec, int type)
+{
+	int gen, zone;
+	bool success = false;
+	struct lrugen *lrugen = &lruvec->evictable;
+
+	VM_BUG_ON(!seq_is_valid(lruvec));
+
+	while (get_nr_gens(lruvec, type) > MIN_NR_GENS) {
+		gen = lru_gen_from_seq(lrugen->min_seq[type]);
+
+		for (zone = 0; zone < MAX_NR_ZONES; zone++) {
+			if (!list_empty(&lrugen->lists[gen][type][zone]))
+				return success;
+		}
+
+		reset_controller_pos(lruvec, gen, type);
+		WRITE_ONCE(lrugen->min_seq[type], lrugen->min_seq[type] + 1);
+
+		success = true;
+	}
+
+	return success;
+}
+
+static bool inc_min_seq(struct lruvec *lruvec, int type)
+{
+	int gen, zone;
+	int batch_size = 0;
+	struct lrugen *lrugen = &lruvec->evictable;
+
+	VM_BUG_ON(!seq_is_valid(lruvec));
+
+	if (get_nr_gens(lruvec, type) != MAX_NR_GENS)
+		return true;
+
+	gen = lru_gen_from_seq(lrugen->min_seq[type]);
+
+	for (zone = 0; zone < MAX_NR_ZONES; zone++) {
+		struct list_head *head = &lrugen->lists[gen][type][zone];
+
+		while (!list_empty(head)) {
+			struct page *page = lru_to_page(head);
+
+			VM_BUG_ON_PAGE(PageTail(page), page);
+			VM_BUG_ON_PAGE(PageUnevictable(page), page);
+			VM_BUG_ON_PAGE(PageActive(page), page);
+			VM_BUG_ON_PAGE(page_is_file_lru(page) != type, page);
+			VM_BUG_ON_PAGE(page_zonenum(page) != zone, page);
+
+			prefetchw_prev_lru_page(page, head, flags);
+
+			page_inc_gen(page, lruvec, false);
+
+			if (++batch_size == MAX_BATCH_SIZE)
+				return false;
+		}
+
+		VM_BUG_ON(lrugen->sizes[gen][type][zone]);
+	}
+
+	reset_controller_pos(lruvec, gen, type);
+	WRITE_ONCE(lrugen->min_seq[type], lrugen->min_seq[type] + 1);
+
+	return true;
+}
+
+static void inc_max_seq(struct lruvec *lruvec)
+{
+	int gen, type, zone;
+	struct lrugen *lrugen = &lruvec->evictable;
+
+	spin_lock_irq(&lruvec->lru_lock);
+
+	VM_BUG_ON(!seq_is_valid(lruvec));
+
+	for (type = 0; type < ANON_AND_FILE; type++) {
+		if (try_inc_min_seq(lruvec, type))
+			continue;
+
+		while (!inc_min_seq(lruvec, type)) {
+			spin_unlock_irq(&lruvec->lru_lock);
+			cond_resched();
+			spin_lock_irq(&lruvec->lru_lock);
+		}
+	}
+
+	gen = lru_gen_from_seq(lrugen->max_seq - 1);
+	for_each_type_zone(type, zone) {
+		enum lru_list lru = type * LRU_FILE;
+		long total = lrugen->sizes[gen][type][zone];
+
+		if (!total)
+			continue;
+
+		WARN_ON_ONCE(total != (int)total);
+
+		update_lru_size(lruvec, lru, zone, total);
+		update_lru_size(lruvec, lru + LRU_ACTIVE, zone, -total);
+	}
+
+	gen = lru_gen_from_seq(lrugen->max_seq + 1);
+	for_each_type_zone(type, zone) {
+		VM_BUG_ON(lrugen->sizes[gen][type][zone]);
+		VM_BUG_ON(!list_empty(&lrugen->lists[gen][type][zone]));
+	}
+
+	for (type = 0; type < ANON_AND_FILE; type++)
+		reset_controller_pos(lruvec, gen, type);
+
+	WRITE_ONCE(lrugen->timestamps[gen], jiffies);
+	/* make sure all preceding modifications appear first */
+	smp_store_release(&lrugen->max_seq, lrugen->max_seq + 1);
+
+	spin_unlock_irq(&lruvec->lru_lock);
+}
+
+/* Main function used by the foreground, the background and the user-triggered aging. */
+static bool walk_mm_list(struct lruvec *lruvec, unsigned long max_seq,
+			 struct scan_control *sc, int swappiness, struct mm_walk_args *args)
+{
+	bool last;
+	bool alloc = !args;
+	struct mm_struct *mm = NULL;
+	struct lrugen *lrugen = &lruvec->evictable;
+	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
+	int nid = pgdat->node_id;
+	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
+	struct lru_gen_mm_list *mm_list = get_mm_list(memcg);
+
+	VM_BUG_ON(max_seq > READ_ONCE(lrugen->max_seq));
+
+	if (alloc) {
+		args = kvzalloc_node(size_of_mm_walk_args(), GFP_KERNEL, nid);
+		if (WARN_ON_ONCE(!args))
+			return false;
+	}
+
+	args->memcg = memcg;
+	args->max_seq = max_seq;
+	args->start_pfn = pgdat->node_start_pfn;
+	args->end_pfn = pgdat_end_pfn(pgdat);
+	args->node_id = nid;
+	args->swappiness = swappiness;
+
+	do {
+		last = get_next_mm(args, &mm);
+		if (mm)
+			walk_mm(args, mm);
+
+		cond_resched();
+	} while (mm);
+
+	if (alloc)
+		kvfree(args);
+
+	if (!last) {
+		/* the foreground aging prefers not to wait */
+		if (!current_is_kswapd() && sc->priority < DEF_PRIORITY - 2)
+			wait_event_killable(mm_list->nodes[nid].wait,
+					    max_seq < READ_ONCE(lrugen->max_seq));
+
+		return max_seq < READ_ONCE(lrugen->max_seq);
+	}
+
+	VM_BUG_ON(max_seq != READ_ONCE(lrugen->max_seq));
+
+	inc_max_seq(lruvec);
+
+	/* order against inc_max_seq() */
+	smp_mb();
+	/* either we see any waiters or they will see updated max_seq */
+	if (waitqueue_active(&mm_list->nodes[nid].wait))
+		wake_up_all(&mm_list->nodes[nid].wait);
+
+	wakeup_flusher_threads(WB_REASON_VMSCAN);
+
+	return true;
+}
+
+void lru_gen_scan_around(struct page_vma_mapped_walk *pvmw)
+{
+	int i;
+	pte_t *pte;
+	int old_gen, new_gen;
+	unsigned long start;
+	unsigned long end;
+	unsigned long addr;
+	struct lruvec *lruvec;
+	struct mem_cgroup *memcg;
+	struct pglist_data *pgdat = page_pgdat(pvmw->page);
+	unsigned long bitmap[BITS_TO_LONGS(SWAP_CLUSTER_MAX * 2)] = {};
+
+	lockdep_assert_held(pvmw->ptl);
+	VM_BUG_ON_PAGE(PageTail(pvmw->page), pvmw->page);
+
+	start = max(pvmw->address & PMD_MASK, pvmw->vma->vm_start);
+	end = pmd_addr_end(pvmw->address, pvmw->vma->vm_end);
+
+	if (end - start > SWAP_CLUSTER_MAX * 2 * PAGE_SIZE) {
+		if (pvmw->address - start < SWAP_CLUSTER_MAX * PAGE_SIZE)
+			end = start + SWAP_CLUSTER_MAX * 2 * PAGE_SIZE;
+		else if (end - pvmw->address < SWAP_CLUSTER_MAX * PAGE_SIZE)
+			start = end - SWAP_CLUSTER_MAX * 2 * PAGE_SIZE;
+		else {
+			start = pvmw->address - SWAP_CLUSTER_MAX * PAGE_SIZE;
+			end = pvmw->address + SWAP_CLUSTER_MAX * PAGE_SIZE;
+		}
+	}
+
+	pte = pvmw->pte - (pvmw->address - start) / PAGE_SIZE;
+
+	arch_enter_lazy_mmu_mode();
+
+	lock_page_memcg(pvmw->page);
+	lruvec = lock_page_lruvec_irq(pvmw->page);
+
+	memcg = page_memcg(pvmw->page);
+	new_gen = lru_gen_from_seq(lruvec->evictable.max_seq);
+
+	for (i = 0, addr = start; addr != end; i++, addr += PAGE_SIZE) {
+		struct page *page;
+		unsigned long pfn = pte_pfn(pte[i]);
+
+		if (!pte_present(pte[i]) || is_zero_pfn(pfn))
+			continue;
+
+		if (WARN_ON_ONCE(pte_devmap(pte[i]) || pte_special(pte[i])))
+			continue;
+
+		if (!pte_young(pte[i]))
+			continue;
+
+		VM_BUG_ON(!pfn_valid(pfn));
+		if (pfn < pgdat->node_start_pfn || pfn >= pgdat_end_pfn(pgdat))
+			continue;
+
+		page = compound_head(pfn_to_page(pfn));
+		if (page_to_nid(page) != pgdat->node_id)
+			continue;
+
+		if (page_memcg_rcu(page) != memcg)
+			continue;
+
+		VM_BUG_ON(addr < pvmw->vma->vm_start || addr >= pvmw->vma->vm_end);
+		if (!ptep_test_and_clear_young(pvmw->vma, addr, pte + i))
+			continue;
+
+		if (pte_dirty(pte[i]) && !PageDirty(page) &&
+		    !(PageAnon(page) && PageSwapBacked(page) && !PageSwapCache(page)))
+			__set_bit(i, bitmap);
+
+		old_gen = page_update_gen(page, new_gen);
+		if (old_gen >= 0 && old_gen != new_gen)
+			lru_gen_update_size(page, lruvec, old_gen, new_gen);
+	}
+
+	unlock_page_lruvec_irq(lruvec);
+	unlock_page_memcg(pvmw->page);
+
+	arch_leave_lazy_mmu_mode();
+
+	for_each_set_bit(i, bitmap, SWAP_CLUSTER_MAX * 2)
+		set_page_dirty(pte_page(pte[i]));
+}
+
 /******************************************************************************
  *                          state change
  ******************************************************************************/
@@ -3415,6 +4199,10 @@ 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);
 
+	VM_BUG_ON(PMD_SIZE / PAGE_SIZE != PTRS_PER_PTE);
+	VM_BUG_ON(PUD_SIZE / PMD_SIZE != PTRS_PER_PMD);
+	VM_BUG_ON(P4D_SIZE / PUD_SIZE != PTRS_PER_PUD);
+
 	if (mem_cgroup_disabled()) {
 		global_mm_list = alloc_mm_list();
 		if (WARN_ON_ONCE(!global_mm_list))
-- 
2.31.1.751.gd2f1c929bd-goog

[PATCH v3 11/14] mm: multigenerational lru: eviction

[Yu Zhao]

The eviction consumes old generations. Given an lruvec, the eviction
scans the pages on the per-zone lists indexed by either of min_seq[2].
It first tries to select a type based on the values of min_seq[2].
When anon and file types are both available from the same generation,
it selects the one that has a lower refault rate.

During a scan, the eviction sorts pages according to their new
generation numbers, if the aging has found them referenced. It also
moves pages from the tiers that have higher refault rates than tier 0
to the next generation. When it finds all the per-zone lists of a
selected type are empty, the eviction increments min_seq[2] indexed by
this selected type.

With the aging and the eviction in place, we can build page reclaim in
a straightforward manner:
  1) In order to reduce the latency, direct reclaim only invokes the
  aging when both min_seq[2] reaches max_seq-1; otherwise it invokes
  the eviction.
  2) In order to avoid the aging in the direct reclaim path, kswapd
  does the background aging. It invokes the aging when either of
  min_seq[2] reaches max_seq-1; otherwise it invokes the eviction.

Signed-off-by: Yu Zhao <yuzhao@google.com>
Tested-by: Konstantin Kharlamov <Hi-Angel@yandex.ru>
---
 include/linux/mmzone.h |   5 +
 mm/vmscan.c            | 540 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 545 insertions(+)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 38de59fcbe54..ded72f44d7e7 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -863,6 +863,8 @@ struct deferred_split {
 };
 #endif
 
+struct mm_walk_args;
+
 /*
  * On NUMA machines, each NUMA node would have a pg_data_t to describe
  * it's memory layout. On UMA machines there is a single pglist_data which
@@ -968,6 +970,9 @@ typedef struct pglist_data {
 
 	unsigned long		flags;
 
+#ifdef CONFIG_LRU_GEN
+	struct mm_walk_args	*mm_walk_args;
+#endif
 	ZONE_PADDING(_pad2_)
 
 	/* Per-node vmstats */
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 837d5e6a821e..2f86dcc04c56 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1311,6 +1311,11 @@ static unsigned int shrink_page_list(struct list_head *page_list,
 		if (!sc->may_unmap && page_mapped(page))
 			goto keep_locked;
 
+		/* in case the page was found accessed by lru_gen_scan_around() */
+		if (lru_gen_enabled() && !ignore_references &&
+		    page_mapped(page) && PageReferenced(page))
+			goto keep_locked;
+
 		may_enter_fs = (sc->gfp_mask & __GFP_FS) ||
 			(PageSwapCache(page) && (sc->gfp_mask & __GFP_IO));
 
@@ -2431,6 +2436,9 @@ static void prepare_scan_count(pg_data_t *pgdat, struct scan_control *sc)
 	unsigned long file;
 	struct lruvec *target_lruvec;
 
+	if (lru_gen_enabled())
+		return;
+
 	target_lruvec = mem_cgroup_lruvec(sc->target_mem_cgroup, pgdat);
 
 	/*
@@ -3970,6 +3978,489 @@ void lru_gen_scan_around(struct page_vma_mapped_walk *pvmw)
 		set_page_dirty(pte_page(pte[i]));
 }
 
+/******************************************************************************
+ *                          the eviction
+ ******************************************************************************/
+
+static bool should_skip_page(struct page *page, struct scan_control *sc)
+{
+	if (!sc->may_unmap && page_mapped(page))
+		return true;
+
+	if (!(sc->may_writepage && (sc->gfp_mask & __GFP_IO)) &&
+	    (PageDirty(page) || (PageAnon(page) && !PageSwapCache(page))))
+		return true;
+
+	if (!get_page_unless_zero(page))
+		return true;
+
+	if (!TestClearPageLRU(page)) {
+		put_page(page);
+		return true;
+	}
+
+	return false;
+}
+
+static bool sort_page(struct page *page, struct lruvec *lruvec, int tier_to_isolate)
+{
+	bool success;
+	int gen = page_lru_gen(page);
+	int type = page_is_file_lru(page);
+	int zone = page_zonenum(page);
+	int tier = lru_tier_from_usage(page_tier_usage(page));
+	struct lrugen *lrugen = &lruvec->evictable;
+
+	VM_BUG_ON_PAGE(gen == -1, page);
+	VM_BUG_ON_PAGE(tier_to_isolate < 0, page);
+
+	/* a lazy-free page that has been written into? */
+	if (type && PageDirty(page) && PageAnon(page)) {
+		success = lru_gen_deletion(page, lruvec);
+		VM_BUG_ON_PAGE(!success, page);
+		SetPageSwapBacked(page);
+		add_page_to_lru_list_tail(page, lruvec);
+		return true;
+	}
+
+	/* page_update_gen() has updated the gen #? */
+	if (gen != lru_gen_from_seq(lrugen->min_seq[type])) {
+		list_move(&page->lru, &lrugen->lists[gen][type][zone]);
+		return true;
+	}
+
+	/* activate this page if its tier has a higher refault rate */
+	if (tier_to_isolate < tier) {
+		int hist = hist_from_seq_or_gen(gen);
+
+		page_inc_gen(page, lruvec, false);
+		WRITE_ONCE(lrugen->activated[hist][type][tier - 1],
+			   lrugen->activated[hist][type][tier - 1] + thp_nr_pages(page));
+		inc_lruvec_state(lruvec, WORKINGSET_ACTIVATE_BASE + type);
+		return true;
+	}
+
+	/* mark this page for reclaim if it's pending writeback */
+	if (PageWriteback(page) || (type && PageDirty(page))) {
+		page_inc_gen(page, lruvec, true);
+		return true;
+	}
+
+	return false;
+}
+
+static void isolate_page(struct page *page, struct lruvec *lruvec)
+{
+	bool success;
+
+	success = lru_gen_deletion(page, lruvec);
+	VM_BUG_ON_PAGE(!success, page);
+
+	if (PageActive(page)) {
+		ClearPageActive(page);
+		/* make sure shrink_page_list() rejects this page */
+		SetPageReferenced(page);
+		return;
+	}
+
+	/* make sure shrink_page_list() doesn't try to write this page */
+	ClearPageReclaim(page);
+	/* make sure shrink_page_list() doesn't reject this page */
+	ClearPageReferenced(page);
+}
+
+static int scan_pages(struct lruvec *lruvec, struct scan_control *sc, long *nr_to_scan,
+		      int type, int tier, struct list_head *list)
+{
+	bool success;
+	int gen, zone;
+	enum vm_event_item item;
+	int sorted = 0;
+	int scanned = 0;
+	int isolated = 0;
+	int batch_size = 0;
+	struct lrugen *lrugen = &lruvec->evictable;
+	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
+
+	VM_BUG_ON(!list_empty(list));
+
+	if (get_nr_gens(lruvec, type) == MIN_NR_GENS)
+		return -ENOENT;
+
+	gen = lru_gen_from_seq(lrugen->min_seq[type]);
+
+	for (zone = sc->reclaim_idx; zone >= 0; zone--) {
+		LIST_HEAD(moved);
+		int skipped = 0;
+		struct list_head *head = &lrugen->lists[gen][type][zone];
+
+		while (!list_empty(head)) {
+			struct page *page = lru_to_page(head);
+			int delta = thp_nr_pages(page);
+
+			VM_BUG_ON_PAGE(PageTail(page), page);
+			VM_BUG_ON_PAGE(PageUnevictable(page), page);
+			VM_BUG_ON_PAGE(PageActive(page), page);
+			VM_BUG_ON_PAGE(page_is_file_lru(page) != type, page);
+			VM_BUG_ON_PAGE(page_zonenum(page) != zone, page);
+
+			prefetchw_prev_lru_page(page, head, flags);
+
+			scanned += delta;
+
+			if (sort_page(page, lruvec, tier))
+				sorted += delta;
+			else if (should_skip_page(page, sc)) {
+				list_move(&page->lru, &moved);
+				skipped += delta;
+			} else {
+				isolate_page(page, lruvec);
+				list_add(&page->lru, list);
+				isolated += delta;
+			}
+
+			if (scanned >= *nr_to_scan || isolated >= SWAP_CLUSTER_MAX ||
+			    ++batch_size == MAX_BATCH_SIZE)
+				break;
+		}
+
+		list_splice(&moved, head);
+		__count_zid_vm_events(PGSCAN_SKIP, zone, skipped);
+
+		if (scanned >= *nr_to_scan || isolated >= SWAP_CLUSTER_MAX ||
+		    batch_size == MAX_BATCH_SIZE)
+			break;
+	}
+
+	success = try_inc_min_seq(lruvec, type);
+
+	item = current_is_kswapd() ? PGSCAN_KSWAPD : PGSCAN_DIRECT;
+	if (!cgroup_reclaim(sc)) {
+		__count_vm_events(item, scanned);
+		__count_vm_events(PGREFILL, sorted);
+	}
+	__count_memcg_events(memcg, item, scanned);
+	__count_memcg_events(memcg, PGREFILL, sorted);
+	__count_vm_events(PGSCAN_ANON + type, scanned);
+
+	*nr_to_scan -= scanned;
+
+	if (*nr_to_scan <= 0 || success || isolated)
+		return isolated;
+	/*
+	 * We may have trouble finding eligible pages due to reclaim_idx,
+	 * may_unmap and may_writepage. The following check makes sure we won't
+	 * be stuck if we aren't making enough progress.
+	 */
+	return batch_size == MAX_BATCH_SIZE && sorted >= SWAP_CLUSTER_MAX ? 0 : -ENOENT;
+}
+
+static int get_tier_to_isolate(struct lruvec *lruvec, int type)
+{
+	int tier;
+	struct controller_pos sp, pv;
+
+	/*
+	 * Ideally we don't want to evict upper tiers that have higher refault
+	 * rates. However, we need to leave a margin for the fluctuations in
+	 * refault rates. So we use a larger gain factor to make sure upper
+	 * tiers are indeed more active. We choose 2 because the lowest upper
+	 * tier would have twice of the refault rate of the base tier, according
+	 * to their numbers of accesses.
+	 */
+	read_controller_pos(&sp, lruvec, type, 0, 1);
+	for (tier = 1; tier < MAX_NR_TIERS; tier++) {
+		read_controller_pos(&pv, lruvec, type, tier, 2);
+		if (!positive_ctrl_err(&sp, &pv))
+			break;
+	}
+
+	return tier - 1;
+}
+
+static int get_type_to_scan(struct lruvec *lruvec, int swappiness, int *tier_to_isolate)
+{
+	int type, tier;
+	struct controller_pos sp, pv;
+	int gain[ANON_AND_FILE] = { swappiness, 200 - swappiness };
+
+	/*
+	 * Compare the refault rates between the base tiers of anon and file to
+	 * determine which type to evict. Also need to compare the refault rates
+	 * of the upper tiers of the selected type with that of the base tier of
+	 * the other type to determine which tier of the selected type to evict.
+	 */
+	read_controller_pos(&sp, lruvec, 0, 0, gain[0]);
+	read_controller_pos(&pv, lruvec, 1, 0, gain[1]);
+	type = positive_ctrl_err(&sp, &pv);
+
+	read_controller_pos(&sp, lruvec, !type, 0, gain[!type]);
+	for (tier = 1; tier < MAX_NR_TIERS; tier++) {
+		read_controller_pos(&pv, lruvec, type, tier, gain[type]);
+		if (!positive_ctrl_err(&sp, &pv))
+			break;
+	}
+
+	*tier_to_isolate = tier - 1;
+
+	return type;
+}
+
+static int isolate_pages(struct lruvec *lruvec, struct scan_control *sc, int swappiness,
+			 long *nr_to_scan, int *type_to_scan, struct list_head *list)
+{
+	int i;
+	int type;
+	int isolated;
+	int tier = -1;
+	DEFINE_MAX_SEQ();
+	DEFINE_MIN_SEQ();
+
+	VM_BUG_ON(!seq_is_valid(lruvec));
+
+	if (max_nr_gens(max_seq, min_seq, swappiness) == MIN_NR_GENS)
+		return 0;
+	/*
+	 * Try to select a type based on generations and swappiness, and if that
+	 * fails, fall back to get_type_to_scan(). When anon and file are both
+	 * available from the same generation, swappiness 200 is interpreted as
+	 * anon first and swappiness 1 is interpreted as file first.
+	 */
+	type = !swappiness || min_seq[0] > min_seq[1] ||
+	       (min_seq[0] == min_seq[1] && swappiness != 200 &&
+		(swappiness == 1 || get_type_to_scan(lruvec, swappiness, &tier)));
+
+	if (tier == -1)
+		tier = get_tier_to_isolate(lruvec, type);
+
+	for (i = !swappiness; i < ANON_AND_FILE; i++) {
+		isolated = scan_pages(lruvec, sc, nr_to_scan, type, tier, list);
+		if (isolated >= 0)
+			break;
+
+		type = !type;
+		tier = get_tier_to_isolate(lruvec, type);
+	}
+
+	if (isolated < 0)
+		isolated = *nr_to_scan = 0;
+
+	*type_to_scan = type;
+
+	return isolated;
+}
+
+/* Main function used by the foreground, the background and the user-triggered eviction. */
+static bool evict_pages(struct lruvec *lruvec, struct scan_control *sc, int swappiness,
+			long *nr_to_scan)
+{
+	int type;
+	int isolated;
+	int reclaimed;
+	LIST_HEAD(list);
+	struct page *page;
+	enum vm_event_item item;
+	struct reclaim_stat stat;
+	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
+
+	spin_lock_irq(&lruvec->lru_lock);
+
+	isolated = isolate_pages(lruvec, sc, swappiness, nr_to_scan, &type, &list);
+	VM_BUG_ON(list_empty(&list) == !!isolated);
+
+	if (isolated)
+		__mod_node_page_state(pgdat, NR_ISOLATED_ANON + type, isolated);
+
+	spin_unlock_irq(&lruvec->lru_lock);
+
+	if (!isolated)
+		goto done;
+
+	reclaimed = shrink_page_list(&list, pgdat, sc, &stat, false);
+	/*
+	 * We need to prevent rejected pages from being added back to the same
+	 * lists they were isolated from. Otherwise we may risk looping on them
+	 * forever. We use PageActive() or !PageReferenced() && PageWorkingset()
+	 * to tell lru_gen_addition() not to add them to the oldest generation.
+	 */
+	list_for_each_entry(page, &list, lru) {
+		if (PageMlocked(page))
+			continue;
+
+		if (page_mapped(page) && PageReferenced(page))
+			SetPageActive(page);
+		else {
+			ClearPageActive(page);
+			SetPageWorkingset(page);
+		}
+		ClearPageReferenced(page);
+	}
+
+	spin_lock_irq(&lruvec->lru_lock);
+
+	move_pages_to_lru(lruvec, &list);
+
+	__mod_node_page_state(pgdat, NR_ISOLATED_ANON + type, -isolated);
+
+	item = current_is_kswapd() ? PGSTEAL_KSWAPD : PGSTEAL_DIRECT;
+	if (!cgroup_reclaim(sc))
+		__count_vm_events(item, reclaimed);
+	__count_memcg_events(lruvec_memcg(lruvec), item, reclaimed);
+	__count_vm_events(PGSTEAL_ANON + type, reclaimed);
+
+	spin_unlock_irq(&lruvec->lru_lock);
+
+	mem_cgroup_uncharge_list(&list);
+	free_unref_page_list(&list);
+
+	sc->nr_reclaimed += reclaimed;
+done:
+	return *nr_to_scan > 0 && sc->nr_reclaimed < sc->nr_to_reclaim;
+}
+
+/******************************************************************************
+ *                          page reclaim
+ ******************************************************************************/
+
+static int get_swappiness(struct lruvec *lruvec)
+{
+	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
+	int swappiness = mem_cgroup_get_nr_swap_pages(memcg) >= (long)SWAP_CLUSTER_MAX ?
+			 mem_cgroup_swappiness(memcg) : 0;
+
+	VM_BUG_ON(swappiness > 200U);
+
+	return swappiness;
+}
+
+static unsigned long get_nr_to_scan(struct lruvec *lruvec, struct scan_control *sc,
+				    int swappiness)
+{
+	int gen, type, zone;
+	long nr_to_scan = 0;
+	struct lrugen *lrugen = &lruvec->evictable;
+	DEFINE_MAX_SEQ();
+	DEFINE_MIN_SEQ();
+
+	lru_add_drain();
+
+	for (type = !swappiness; type < ANON_AND_FILE; type++) {
+		unsigned long seq;
+
+		for (seq = min_seq[type]; seq <= max_seq; seq++) {
+			gen = lru_gen_from_seq(seq);
+
+			for (zone = 0; zone <= sc->reclaim_idx; zone++)
+				nr_to_scan += READ_ONCE(lrugen->sizes[gen][type][zone]);
+		}
+	}
+
+	nr_to_scan = max(nr_to_scan, 0L);
+	nr_to_scan = round_up(nr_to_scan >> sc->priority, SWAP_CLUSTER_MAX);
+
+	if (max_nr_gens(max_seq, min_seq, swappiness) > MIN_NR_GENS)
+		return nr_to_scan;
+
+	/* kswapd uses lru_gen_age_node() */
+	if (current_is_kswapd())
+		return 0;
+
+	return walk_mm_list(lruvec, max_seq, sc, swappiness, NULL) ? nr_to_scan : 0;
+}
+
+static void lru_gen_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
+{
+	struct blk_plug plug;
+	unsigned long scanned = 0;
+	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
+
+	blk_start_plug(&plug);
+
+	while (true) {
+		long nr_to_scan;
+		int swappiness = sc->may_swap ? get_swappiness(lruvec) : 0;
+
+		nr_to_scan = get_nr_to_scan(lruvec, sc, swappiness) - scanned;
+		if (nr_to_scan < (long)SWAP_CLUSTER_MAX)
+			break;
+
+		scanned += nr_to_scan;
+
+		if (!evict_pages(lruvec, sc, swappiness, &nr_to_scan))
+			break;
+
+		scanned -= nr_to_scan;
+
+		if (mem_cgroup_below_min(memcg) ||
+		    (mem_cgroup_below_low(memcg) && !sc->memcg_low_reclaim))
+			break;
+
+		cond_resched();
+	}
+
+	blk_finish_plug(&plug);
+}
+
+/******************************************************************************
+ *                          the background aging
+ ******************************************************************************/
+
+static int lru_gen_spread = MIN_NR_GENS;
+
+static void try_walk_mm_list(struct lruvec *lruvec, struct scan_control *sc)
+{
+	int gen, type, zone;
+	long old_and_young[2] = {};
+	int spread = READ_ONCE(lru_gen_spread);
+	int swappiness = get_swappiness(lruvec);
+	struct lrugen *lrugen = &lruvec->evictable;
+	struct pglist_data *pgdat = lruvec_pgdat(lruvec);
+	DEFINE_MAX_SEQ();
+	DEFINE_MIN_SEQ();
+
+	lru_add_drain();
+
+	for (type = !swappiness; type < ANON_AND_FILE; type++) {
+		unsigned long seq;
+
+		for (seq = min_seq[type]; seq <= max_seq; seq++) {
+			gen = lru_gen_from_seq(seq);
+
+			for (zone = 0; zone < MAX_NR_ZONES; zone++)
+				old_and_young[seq == max_seq] +=
+					READ_ONCE(lrugen->sizes[gen][type][zone]);
+		}
+	}
+
+	old_and_young[0] = max(old_and_young[0], 0L);
+	old_and_young[1] = max(old_and_young[1], 0L);
+
+	/* try to spread pages out across spread+1 generations */
+	if (old_and_young[0] >= old_and_young[1] * spread &&
+	    min_nr_gens(max_seq, min_seq, swappiness) > max(spread, MIN_NR_GENS))
+		return;
+
+	walk_mm_list(lruvec, max_seq, sc, swappiness, pgdat->mm_walk_args);
+}
+
+static void lru_gen_age_node(struct pglist_data *pgdat, struct scan_control *sc)
+{
+	struct mem_cgroup *memcg;
+
+	VM_BUG_ON(!current_is_kswapd());
+
+	memcg = mem_cgroup_iter(NULL, NULL, NULL);
+	do {
+		struct lruvec *lruvec = mem_cgroup_lruvec(memcg, pgdat);
+
+		if (!mem_cgroup_below_min(memcg) &&
+		    (!mem_cgroup_below_low(memcg) || sc->memcg_low_reclaim))
+			try_walk_mm_list(lruvec, sc);
+
+		cond_resched();
+	} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)));
+}
+
 /******************************************************************************
  *                          state change
  ******************************************************************************/
@@ -4172,6 +4663,21 @@ static int __meminit __maybe_unused lru_gen_online_mem(struct notifier_block *se
 	return NOTIFY_DONE;
 }
 
+static void lru_gen_start_kswapd(int nid)
+{
+	struct pglist_data *pgdat = NODE_DATA(nid);
+
+	pgdat->mm_walk_args = kvzalloc_node(size_of_mm_walk_args(), GFP_KERNEL, nid);
+	WARN_ON_ONCE(!pgdat->mm_walk_args);
+}
+
+static void lru_gen_stop_kswapd(int nid)
+{
+	struct pglist_data *pgdat = NODE_DATA(nid);
+
+	kvfree(pgdat->mm_walk_args);
+}
+
 /******************************************************************************
  *                          initialization
  ******************************************************************************/
@@ -4220,6 +4726,24 @@ static int __init init_lru_gen(void)
  */
 arch_initcall(init_lru_gen);
 
+#else /* CONFIG_LRU_GEN */
+
+static void lru_gen_shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
+{
+}
+
+static void lru_gen_age_node(struct pglist_data *pgdat, struct scan_control *sc)
+{
+}
+
+static void lru_gen_start_kswapd(int nid)
+{
+}
+
+static void lru_gen_stop_kswapd(int nid)
+{
+}
+
 #endif /* CONFIG_LRU_GEN */
 
 static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
@@ -4233,6 +4757,11 @@ static void shrink_lruvec(struct lruvec *lruvec, struct scan_control *sc)
 	struct blk_plug plug;
 	bool scan_adjusted;
 
+	if (lru_gen_enabled()) {
+		lru_gen_shrink_lruvec(lruvec, sc);
+		return;
+	}
+
 	get_scan_count(lruvec, sc, nr);
 
 	/* Record the original scan target for proportional adjustments later */
@@ -4699,6 +5228,9 @@ static void snapshot_refaults(struct mem_cgroup *target_memcg, pg_data_t *pgdat)
 	struct lruvec *target_lruvec;
 	unsigned long refaults;
 
+	if (lru_gen_enabled())
+		return;
+
 	target_lruvec = mem_cgroup_lruvec(target_memcg, pgdat);
 	refaults = lruvec_page_state(target_lruvec, WORKINGSET_ACTIVATE_ANON);
 	target_lruvec->refaults[0] = refaults;
@@ -5073,6 +5605,11 @@ static void age_active_anon(struct pglist_data *pgdat,
 	struct mem_cgroup *memcg;
 	struct lruvec *lruvec;
 
+	if (lru_gen_enabled()) {
+		lru_gen_age_node(pgdat, sc);
+		return;
+	}
+
 	if (!total_swap_pages)
 		return;
 
@@ -5753,6 +6290,8 @@ int kswapd_run(int nid)
 	if (pgdat->kswapd)
 		return 0;
 
+	lru_gen_start_kswapd(nid);
+
 	pgdat->kswapd = kthread_run(kswapd, pgdat, "kswapd%d", nid);
 	if (IS_ERR(pgdat->kswapd)) {
 		/* failure at boot is fatal */
@@ -5775,6 +6314,7 @@ void kswapd_stop(int nid)
 	if (kswapd) {
 		kthread_stop(kswapd);
 		NODE_DATA(nid)->kswapd = NULL;
+		lru_gen_stop_kswapd(nid);
 	}
 }
 
-- 
2.31.1.751.gd2f1c929bd-goog

[PATCH v3 12/14] mm: multigenerational lru: user interface

[Yu Zhao]

Add a sysfs file /sys/kernel/mm/lru_gen/enabled to enable and disable
the multigenerational lru at runtime.

Add a sysfs file /sys/kernel/mm/lru_gen/spread to optionally spread
pages out across more than three generations. More generations make
the background aging more aggressive.

Add a debugfs file /sys/kernel/debug/lru_gen to monitor the
multigenerational lru and trigger the aging and the eviction. This
file has the following output:
  memcg  memcg_id  memcg_path
    node  node_id
      min_gen  birth_time  anon_size  file_size
      ...
      max_gen  birth_time  anon_size  file_size

Given a memcg and a node, "min_gen" is the oldest generation (number)
and "max_gen" is the youngest. Birth time is in milliseconds. The
sizes of anon and file types are in pages.

This file takes the following input:
  + memcg_id node_id gen [swappiness]
  - memcg_id node_id gen [swappiness] [nr_to_reclaim]

The first command line accounts referenced pages to generation
"max_gen" and creates the next generation "max_gen"+1. In this case,
"gen" should be equal to "max_gen". A swap file and a non-zero
"swappiness" are required to scan anon type. If swapping is not
desired, set vm.swappiness to 0. The second command line evicts
generations less than or equal to "gen". In this case, "gen" should be
less than "max_gen"-1 as "max_gen" and "max_gen"-1 are active
generations and therefore protected from the eviction. Use
"nr_to_reclaim" to limit the number of pages to evict. Multiple
command lines are supported, so does concatenation with delimiters ","
and ";".

Signed-off-by: Yu Zhao <yuzhao@google.com>
Tested-by: Konstantin Kharlamov <Hi-Angel@yandex.ru>
---
 mm/vmscan.c | 403 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 403 insertions(+)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 2f86dcc04c56..ff2deec24c64 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -52,6 +52,8 @@
 #include <linux/memory.h>
 #include <linux/pagewalk.h>
 #include <linux/shmem_fs.h>
+#include <linux/ctype.h>
+#include <linux/debugfs.h>
 
 #include <asm/tlbflush.h>
 #include <asm/div64.h>
@@ -4678,6 +4680,401 @@ static void lru_gen_stop_kswapd(int nid)
 	kvfree(pgdat->mm_walk_args);
 }
 
+/******************************************************************************
+ *                          sysfs interface
+ ******************************************************************************/
+
+static ssize_t show_lru_gen_spread(struct kobject *kobj, struct kobj_attribute *attr,
+				   char *buf)
+{
+	return sprintf(buf, "%d\n", READ_ONCE(lru_gen_spread));
+}
+
+static ssize_t store_lru_gen_spread(struct kobject *kobj, struct kobj_attribute *attr,
+				    const char *buf, size_t len)
+{
+	int spread;
+
+	if (kstrtoint(buf, 10, &spread) || spread >= MAX_NR_GENS)
+		return -EINVAL;
+
+	WRITE_ONCE(lru_gen_spread, spread);
+
+	return len;
+}
+
+static struct kobj_attribute lru_gen_spread_attr = __ATTR(
+	spread, 0644, show_lru_gen_spread, store_lru_gen_spread
+);
+
+static ssize_t show_lru_gen_enabled(struct kobject *kobj, struct kobj_attribute *attr,
+				    char *buf)
+{
+	return snprintf(buf, PAGE_SIZE, "%d\n", lru_gen_enabled());
+}
+
+static ssize_t store_lru_gen_enabled(struct kobject *kobj, struct kobj_attribute *attr,
+				     const char *buf, size_t len)
+{
+	int enable;
+
+	if (kstrtoint(buf, 10, &enable))
+		return -EINVAL;
+
+	lru_gen_set_state(enable, true, false);
+
+	return len;
+}
+
+static struct kobj_attribute lru_gen_enabled_attr = __ATTR(
+	enabled, 0644, show_lru_gen_enabled, store_lru_gen_enabled
+);
+
+static struct attribute *lru_gen_attrs[] = {
+	&lru_gen_spread_attr.attr,
+	&lru_gen_enabled_attr.attr,
+	NULL
+};
+
+static struct attribute_group lru_gen_attr_group = {
+	.name = "lru_gen",
+	.attrs = lru_gen_attrs,
+};
+
+/******************************************************************************
+ *                          debugfs interface
+ ******************************************************************************/
+
+static void *lru_gen_seq_start(struct seq_file *m, loff_t *pos)
+{
+	struct mem_cgroup *memcg;
+	loff_t nr_to_skip = *pos;
+
+	m->private = kzalloc(PATH_MAX, GFP_KERNEL);
+	if (!m->private)
+		return ERR_PTR(-ENOMEM);
+
+	memcg = mem_cgroup_iter(NULL, NULL, NULL);
+	do {
+		int nid;
+
+		for_each_node_state(nid, N_MEMORY) {
+			if (!nr_to_skip--)
+				return mem_cgroup_lruvec(memcg, NODE_DATA(nid));
+		}
+	} while ((memcg = mem_cgroup_iter(NULL, memcg, NULL)));
+
+	return NULL;
+}
+
+static void lru_gen_seq_stop(struct seq_file *m, void *v)
+{
+	if (!IS_ERR_OR_NULL(v))
+		mem_cgroup_iter_break(NULL, lruvec_memcg(v));
+
+	kfree(m->private);
+	m->private = NULL;
+}
+
+static void *lru_gen_seq_next(struct seq_file *m, void *v, loff_t *pos)
+{
+	int nid = lruvec_pgdat(v)->node_id;
+	struct mem_cgroup *memcg = lruvec_memcg(v);
+
+	++*pos;
+
+	nid = next_memory_node(nid);
+	if (nid == MAX_NUMNODES) {
+		memcg = mem_cgroup_iter(NULL, memcg, NULL);
+		if (!memcg)
+			return NULL;
+
+		nid = first_memory_node;
+	}
+
+	return mem_cgroup_lruvec(memcg, NODE_DATA(nid));
+}
+
+static void lru_gen_seq_show_full(struct seq_file *m, struct lruvec *lruvec,
+				  unsigned long max_seq, unsigned long *min_seq,
+				  unsigned long seq)
+{
+	int i;
+	int type, tier;
+	int hist = hist_from_seq_or_gen(seq);
+	struct lrugen *lrugen = &lruvec->evictable;
+	int nid = lruvec_pgdat(lruvec)->node_id;
+	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
+	struct lru_gen_mm_list *mm_list = get_mm_list(memcg);
+
+	for (tier = 0; tier < MAX_NR_TIERS; tier++) {
+		seq_printf(m, "            %10d", tier);
+		for (type = 0; type < ANON_AND_FILE; type++) {
+			unsigned long n[3] = {};
+
+			if (seq == max_seq) {
+				n[0] = READ_ONCE(lrugen->avg_refaulted[type][tier]);
+				n[1] = READ_ONCE(lrugen->avg_total[type][tier]);
+
+				seq_printf(m, " %10luR %10luT %10lu ", n[0], n[1], n[2]);
+			} else if (seq == min_seq[type] || NR_STAT_GENS > 1) {
+				n[0] = atomic_long_read(&lrugen->refaulted[hist][type][tier]);
+				n[1] = atomic_long_read(&lrugen->evicted[hist][type][tier]);
+				if (tier)
+					n[2] = READ_ONCE(lrugen->activated[hist][type][tier - 1]);
+
+				seq_printf(m, " %10lur %10lue %10lua", n[0], n[1], n[2]);
+			} else
+				seq_puts(m, "          0           0           0 ");
+		}
+		seq_putc(m, '\n');
+	}
+
+	seq_puts(m, "                      ");
+	for (i = 0; i < NR_MM_STATS; i++) {
+		if (seq == max_seq && NR_STAT_GENS == 1)
+			seq_printf(m, " %10lu%c", READ_ONCE(mm_list->nodes[nid].stats[hist][i]),
+				   toupper(MM_STAT_CODES[i]));
+		else if (seq != max_seq && NR_STAT_GENS > 1)
+			seq_printf(m, " %10lu%c", READ_ONCE(mm_list->nodes[nid].stats[hist][i]),
+				   MM_STAT_CODES[i]);
+		else
+			seq_puts(m, "          0 ");
+	}
+	seq_putc(m, '\n');
+}
+
+static int lru_gen_seq_show(struct seq_file *m, void *v)
+{
+	unsigned long seq;
+	bool full = !debugfs_real_fops(m->file)->write;
+	struct lruvec *lruvec = v;
+	struct lrugen *lrugen = &lruvec->evictable;
+	int nid = lruvec_pgdat(lruvec)->node_id;
+	struct mem_cgroup *memcg = lruvec_memcg(lruvec);
+	DEFINE_MAX_SEQ();
+	DEFINE_MIN_SEQ();
+
+	if (nid == first_memory_node) {
+#ifdef CONFIG_MEMCG
+		if (memcg)
+			cgroup_path(memcg->css.cgroup, m->private, PATH_MAX);
+#endif
+		seq_printf(m, "memcg %5hu %s\n", mem_cgroup_id(memcg), (char *)m->private);
+	}
+
+	seq_printf(m, " node %5d\n", nid);
+
+	seq = full ? (max_seq < MAX_NR_GENS ? 0 : max_seq - MAX_NR_GENS + 1) :
+		     min(min_seq[0], min_seq[1]);
+
+	for (; seq <= max_seq; seq++) {
+		int gen, type, zone;
+		unsigned int msecs;
+
+		gen = lru_gen_from_seq(seq);
+		msecs = jiffies_to_msecs(jiffies - READ_ONCE(lrugen->timestamps[gen]));
+
+		seq_printf(m, " %10lu %10u", seq, msecs);
+
+		for (type = 0; type < ANON_AND_FILE; type++) {
+			long size = 0;
+
+			if (seq < min_seq[type]) {
+				seq_puts(m, "         -0 ");
+				continue;
+			}
+
+			for (zone = 0; zone < MAX_NR_ZONES; zone++)
+				size += READ_ONCE(lrugen->sizes[gen][type][zone]);
+
+			seq_printf(m, " %10lu ", max(size, 0L));
+		}
+
+		seq_putc(m, '\n');
+
+		if (full)
+			lru_gen_seq_show_full(m, lruvec, max_seq, min_seq, seq);
+	}
+
+	return 0;
+}
+
+static const struct seq_operations lru_gen_seq_ops = {
+	.start = lru_gen_seq_start,
+	.stop = lru_gen_seq_stop,
+	.next = lru_gen_seq_next,
+	.show = lru_gen_seq_show,
+};
+
+static int advance_max_seq(struct lruvec *lruvec, unsigned long seq, int swappiness)
+{
+	struct scan_control sc = {
+		.target_mem_cgroup = lruvec_memcg(lruvec),
+	};
+	DEFINE_MAX_SEQ();
+
+	if (seq == max_seq)
+		walk_mm_list(lruvec, max_seq, &sc, swappiness, NULL);
+
+	return seq > max_seq ? -EINVAL : 0;
+}
+
+static int advance_min_seq(struct lruvec *lruvec, unsigned long seq, int swappiness,
+			   unsigned long nr_to_reclaim)
+{
+	struct blk_plug plug;
+	int err = -EINTR;
+	long nr_to_scan = LONG_MAX;
+	struct scan_control sc = {
+		.nr_to_reclaim = nr_to_reclaim,
+		.target_mem_cgroup = lruvec_memcg(lruvec),
+		.may_writepage = 1,
+		.may_unmap = 1,
+		.may_swap = 1,
+		.reclaim_idx = MAX_NR_ZONES - 1,
+		.gfp_mask = GFP_KERNEL,
+	};
+	DEFINE_MAX_SEQ();
+
+	if (seq >= max_seq - 1)
+		return -EINVAL;
+
+	blk_start_plug(&plug);
+
+	while (!signal_pending(current)) {
+		DEFINE_MIN_SEQ();
+
+		if (seq < min(min_seq[!swappiness], min_seq[swappiness < 200]) ||
+		    !evict_pages(lruvec, &sc, swappiness, &nr_to_scan)) {
+			err = 0;
+			break;
+		}
+
+		cond_resched();
+	}
+
+	blk_finish_plug(&plug);
+
+	return err;
+}
+
+static int advance_seq(char cmd, int memcg_id, int nid, unsigned long seq,
+		       int swappiness, unsigned long nr_to_reclaim)
+{
+	struct lruvec *lruvec;
+	int err = -EINVAL;
+	struct mem_cgroup *memcg = NULL;
+
+	if (!mem_cgroup_disabled()) {
+		rcu_read_lock();
+		memcg = mem_cgroup_from_id(memcg_id);
+#ifdef CONFIG_MEMCG
+		if (memcg && !css_tryget(&memcg->css))
+			memcg = NULL;
+#endif
+		rcu_read_unlock();
+
+		if (!memcg)
+			goto done;
+	}
+	if (memcg_id != mem_cgroup_id(memcg))
+		goto done;
+
+	if (nid < 0 || nid >= MAX_NUMNODES || !node_state(nid, N_MEMORY))
+		goto done;
+
+	lruvec = mem_cgroup_lruvec(memcg, NODE_DATA(nid));
+
+	if (swappiness == -1)
+		swappiness = get_swappiness(lruvec);
+	else if (swappiness > 200U)
+		goto done;
+
+	switch (cmd) {
+	case '+':
+		err = advance_max_seq(lruvec, seq, swappiness);
+		break;
+	case '-':
+		err = advance_min_seq(lruvec, seq, swappiness, nr_to_reclaim);
+		break;
+	}
+done:
+	mem_cgroup_put(memcg);
+
+	return err;
+}
+
+static ssize_t lru_gen_seq_write(struct file *file, const char __user *src,
+				 size_t len, loff_t *pos)
+{
+	void *buf;
+	char *cur, *next;
+	int err = 0;
+
+	buf = kvmalloc(len + 1, GFP_USER);
+	if (!buf)
+		return -ENOMEM;
+
+	if (copy_from_user(buf, src, len)) {
+		kvfree(buf);
+		return -EFAULT;
+	}
+
+	next = buf;
+	next[len] = '\0';
+
+	while ((cur = strsep(&next, ",;\n"))) {
+		int n;
+		int end;
+		char cmd;
+		unsigned int memcg_id;
+		unsigned int nid;
+		unsigned long seq;
+		unsigned int swappiness = -1;
+		unsigned long nr_to_reclaim = -1;
+
+		cur = skip_spaces(cur);
+		if (!*cur)
+			continue;
+
+		n = sscanf(cur, "%c %u %u %lu %n %u %n %lu %n", &cmd, &memcg_id, &nid,
+			   &seq, &end, &swappiness, &end, &nr_to_reclaim, &end);
+		if (n < 4 || cur[end]) {
+			err = -EINVAL;
+			break;
+		}
+
+		err = advance_seq(cmd, memcg_id, nid, seq, swappiness, nr_to_reclaim);
+		if (err)
+			break;
+	}
+
+	kvfree(buf);
+
+	return err ? : len;
+}
+
+static int lru_gen_seq_open(struct inode *inode, struct file *file)
+{
+	return seq_open(file, &lru_gen_seq_ops);
+}
+
+static const struct file_operations lru_gen_rw_fops = {
+	.open = lru_gen_seq_open,
+	.read = seq_read,
+	.write = lru_gen_seq_write,
+	.llseek = seq_lseek,
+	.release = seq_release,
+};
+
+static const struct file_operations lru_gen_ro_fops = {
+	.open = lru_gen_seq_open,
+	.read = seq_read,
+	.llseek = seq_lseek,
+	.release = seq_release,
+};
+
 /******************************************************************************
  *                          initialization
  ******************************************************************************/
@@ -4718,6 +5115,12 @@ static int __init init_lru_gen(void)
 	if (hotplug_memory_notifier(lru_gen_online_mem, 0))
 		pr_err("lru_gen: failed to subscribe hotplug notifications\n");
 
+	if (sysfs_create_group(mm_kobj, &lru_gen_attr_group))
+		pr_err("lru_gen: failed to create sysfs group\n");
+
+	debugfs_create_file("lru_gen", 0644, NULL, NULL, &lru_gen_rw_fops);
+	debugfs_create_file("lru_gen_full", 0444, NULL, NULL, &lru_gen_ro_fops);
+
 	return 0;
 };
 /*
-- 
2.31.1.751.gd2f1c929bd-goog

[PATCH v3 13/14] mm: multigenerational lru: Kconfig

[Yu Zhao]

Add configuration options for the multigenerational lru.

Signed-off-by: Yu Zhao <yuzhao@google.com>
Tested-by: Konstantin Kharlamov <Hi-Angel@yandex.ru>
---
 mm/Kconfig | 58 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 58 insertions(+)

diff --git a/mm/Kconfig b/mm/Kconfig
index 02d44e3420f5..da125f145bc4 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -901,4 +901,62 @@ config KMAP_LOCAL
 # struct io_mapping based helper.  Selected by drivers that need them
 config IO_MAPPING
 	bool
+
+# the multigenerational lru {
+config LRU_GEN
+	bool "Multigenerational LRU"
+	depends on MMU
+	help
+	  A high performance LRU implementation to heavily overcommit workloads
+	  that are not IO bound. See Documentation/vm/multigen_lru.rst for
+	  details.
+
+	  Warning: do not enable this option unless you plan to use it because
+	  it introduces a small per-process and per-memcg and per-node memory
+	  overhead.
+
+config LRU_GEN_ENABLED
+	bool "Turn on by default"
+	depends on LRU_GEN
+	help
+	  The default value of /sys/kernel/mm/lru_gen/enabled is 0. This option
+	  changes it to 1.
+
+	  Warning: the default value is the fast path. See
+	  Documentation/static-keys.txt for details.
+
+config LRU_GEN_STATS
+	bool "Full stats for debugging"
+	depends on LRU_GEN
+	help
+	  This option keeps full stats for each generation, which can be read
+	  from /sys/kernel/debug/lru_gen_full.
+
+	  Warning: do not enable this option unless you plan to use it because
+	  it introduces an additional small per-process and per-memcg and
+	  per-node memory overhead.
+
+config NR_LRU_GENS
+	int "Max number of generations"
+	depends on LRU_GEN
+	range 4 31
+	default 7
+	help
+	  This will use order_base_2(N+1) spare bits from page flags.
+
+	  Warning: do not use numbers larger than necessary because each
+	  generation introduces a small per-node and per-memcg memory overhead.
+
+config TIERS_PER_GEN
+	int "Number of tiers per generation"
+	depends on LRU_GEN
+	range 2 5
+	default 4
+	help
+	  This will use N-2 spare bits from page flags.
+
+	  Larger values generally offer better protection to active pages under
+	  heavy buffered I/O workloads.
+# }
+
 endmenu
-- 
2.31.1.751.gd2f1c929bd-goog

[PATCH v3 14/14] mm: multigenerational lru: documentation

[Yu Zhao]

Add Documentation/vm/multigen_lru.rst.

Signed-off-by: Yu Zhao <yuzhao@google.com>
Tested-by: Konstantin Kharlamov <Hi-Angel@yandex.ru>
---
 Documentation/vm/index.rst        |   1 +
 Documentation/vm/multigen_lru.rst | 143 ++++++++++++++++++++++++++++++
 2 files changed, 144 insertions(+)
 create mode 100644 Documentation/vm/multigen_lru.rst

diff --git a/Documentation/vm/index.rst b/Documentation/vm/index.rst
index eff5fbd492d0..c353b3f55924 100644
--- a/Documentation/vm/index.rst
+++ b/Documentation/vm/index.rst
@@ -17,6 +17,7 @@ various features of the Linux memory management
 
    swap_numa
    zswap
+   multigen_lru
 
 Kernel developers MM documentation
 ==================================
diff --git a/Documentation/vm/multigen_lru.rst b/Documentation/vm/multigen_lru.rst
new file mode 100644
index 000000000000..a18416ed7e92
--- /dev/null
+++ b/Documentation/vm/multigen_lru.rst
@@ -0,0 +1,143 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+=====================
+Multigenerational LRU
+=====================
+
+Quick Start
+===========
+Build Options
+-------------
+:Required: Set ``CONFIG_LRU_GEN=y``.
+
+:Optional: Set ``CONFIG_LRU_GEN_ENABLED=y`` to turn the feature on by
+ default.
+
+:Optional: Change ``CONFIG_NR_LRU_GENS`` to a number ``X`` to support
+ a maximum of ``X`` generations.
+
+:Optional: Change ``CONFIG_TIERS_PER_GEN`` to a number ``Y`` to
+ support a maximum of ``Y`` tiers per generation.
+
+Runtime Options
+---------------
+:Required: Write ``1`` to ``/sys/kernel/mm/lru_gen/enable`` if the
+ feature was not turned on by default.
+
+:Optional: Change ``/sys/kernel/mm/lru_gen/spread`` to a number ``N``
+ to spread pages out across ``N+1`` generations. ``N`` should be less
+ than ``X``. Larger values make the background aging more aggressive.
+
+:Optional: Read ``/sys/kernel/debug/lru_gen`` to verify the feature.
+ This file has the following output:
+
+::
+
+  memcg  memcg_id  memcg_path
+    node  node_id
+      min_gen  birth_time  anon_size  file_size
+      ...
+      max_gen  birth_time  anon_size  file_size
+
+Given a memcg and a node, ``min_gen`` is the oldest generation
+(number) and ``max_gen`` is the youngest. Birth time is in
+milliseconds. The sizes of anon and file types are in pages.
+
+Recipes
+-------
+:Android on ARMv8.1+: ``X=4``, ``Y=3`` and ``N=0``.
+
+:Android on pre-ARMv8.1 CPUs: Not recommended due to the lack of
+ ``ARM64_HW_AFDBM``.
+
+:Laptops and workstations running Chrome on x86_64: Use the default
+ values.
+
+:Working set estimation: Write ``+ memcg_id node_id gen [swappiness]``
+ to ``/sys/kernel/debug/lru_gen`` to account referenced pages to
+ generation ``max_gen`` and create the next generation ``max_gen+1``.
+ ``gen`` should be equal to ``max_gen``. A swap file and a non-zero
+ ``swappiness`` are required to scan anon type. If swapping is not
+ desired, set ``vm.swappiness`` to ``0``.
+
+:Proactive reclaim: Write ``- memcg_id node_id gen [swappiness]
+ [nr_to_reclaim]`` to ``/sys/kernel/debug/lru_gen`` to evict
+ generations less than or equal to ``gen``. ``gen`` should be less
+ than ``max_gen-1`` as ``max_gen`` and ``max_gen-1`` are active
+ generations and therefore protected from the eviction. Use
+ ``nr_to_reclaim`` to limit the number of pages to evict. Multiple
+ command lines are supported, so does concatenation with delimiters
+ ``,`` and ``;``.
+
+Framework
+=========
+For each ``lruvec``, evictable pages are divided into multiple
+generations. The youngest generation number is stored in ``max_seq``
+for both anon and file types as they are aged on an equal footing. The
+oldest generation numbers are stored in ``min_seq[2]`` separately for
+anon and file types as clean file pages can be evicted regardless of
+swap and write-back constraints. These three variables are
+monotonically increasing. Generation numbers are truncated into
+``order_base_2(CONFIG_NR_LRU_GENS+1)`` bits in order to fit into
+``page->flags``. The sliding window technique is used to prevent
+truncated generation numbers from overlapping. Each truncated
+generation number is an index to an array of per-type and per-zone
+lists. Evictable pages are added to the per-zone lists indexed by
+``max_seq`` or ``min_seq[2]`` (modulo ``CONFIG_NR_LRU_GENS``),
+depending on their types.
+
+Each generation is then divided into multiple tiers. Tiers represent
+levels of usage from file descriptors only. Pages accessed N times via
+file descriptors belong to tier order_base_2(N). Each generation
+contains at most CONFIG_TIERS_PER_GEN tiers, and they require
+additional CONFIG_TIERS_PER_GEN-2 bits in page->flags. In contrast to
+moving across generations which requires the lru lock for the list
+operations, moving across tiers only involves an atomic operation on
+``page->flags`` and therefore has a negligible cost. A feedback loop
+modeled after the PID controller monitors the refault rates across all
+tiers and decides when to activate pages from which tiers in the
+reclaim path.
+
+The framework comprises two conceptually independent components: the
+aging and the eviction, which can be invoked separately from user
+space for the purpose of working set estimation and proactive reclaim.
+
+Aging
+-----
+The aging produces young generations. Given an ``lruvec``, the aging
+scans page tables for referenced pages of this ``lruvec``. Upon
+finding one, the aging updates its generation number to ``max_seq``.
+After each round of scan, the aging increments ``max_seq``.
+
+The aging maintains either a system-wide ``mm_struct`` list or
+per-memcg ``mm_struct`` lists, and it only scans page tables of
+processes that have been scheduled since the last scan.
+
+The aging is due when both of ``min_seq[2]`` reaches ``max_seq-1``,
+assuming both anon and file types are reclaimable.
+
+Eviction
+--------
+The eviction consumes old generations. Given an ``lruvec``, the
+eviction scans the pages on the per-zone lists indexed by either of
+``min_seq[2]``. It first tries to select a type based on the values of
+``min_seq[2]``. When anon and file types are both available from the
+same generation, it selects the one that has a lower refault rate.
+
+During a scan, the eviction sorts pages according to their new
+generation numbers, if the aging has found them referenced. It also
+moves pages from the tiers that have higher refault rates than tier 0
+to the next generation.
+
+When it finds all the per-zone lists of a selected type are empty, the
+eviction increments ``min_seq[2]`` indexed by this selected type.
+
+To-do List
+==========
+KVM Optimization
+----------------
+Support shadow page table scanning.
+
+NUMA Optimization
+-----------------
+Optimize page table scan for NUMA.
-- 
2.31.1.751.gd2f1c929bd-goog

Re: [PATCH v3 00/14] Multigenerational LRU Framework

[Hillf Danton]

On Thu, 20 May 2021 00:53:41 -0600 Yu Zhao wrote:
> 
> What's new in v3
> ================
> 1) Fixed a bug reported by the Arch Linux kernel team:
>    https://github.com/zen-kernel/zen-kernel/issues/207
> 2) Rebased to v5.13-rc2.

Given no reply within two months, feel free to spin, would-be Mr Kswapd.

Hillf

Re: [PATCH v3 00/14] Multigenerational LRU Framework

[Yu Zhao]

On Tue, Jul 27, 2021 at 7:59 PM Hillf Danton <hdanton@sina.com> wrote:
>
> On Thu, 20 May 2021 00:53:41 -0600 Yu Zhao wrote:
> >
> > What's new in v3
> > ================
> > 1) Fixed a bug reported by the Arch Linux kernel team:
> >    https://github.com/zen-kernel/zen-kernel/issues/207
> > 2) Rebased to v5.13-rc2.
>
> Given no reply within two months, feel free to spin, would-be Mr Kswapd.

Thanks for the reminder. Will gladly get on it sometime this week.

Re: [PATCH v3 00/14] Multigenerational LRU Framework

[Hillf Danton]

[-- Attachment #1: Type: text/plain, Size: 436 bytes --]

On 7 Aug 2021 14:04 Alexey Avramov wrote:
>
>>Given no reply within two months
>
>We are discussing mgLRU outside the mailing lists.
>Some issues have been found, some have been resolved[1], some are still pending[2].

Thanks for sharing that.
What was preventing you from solving the issues at linux-mm?

>[1] https://github.com/zen-kernel/zen-kernel/issues/216
>[2] https://github.com/zen-kernel/zen-kernel/issues/223



[-- Attachment #2: Type: text/html, Size: 2562 bytes --]