[PATCH mm-unstable v1 4/7] mm: multi-gen LRU: section for memcg LRU
From: T.J. Alumbaugh
Date: Tue Jan 17 2023 - 19:42:26 EST
Move memcg LRU code into a dedicated section. Improve the design
doc to outline its architecture.
Signed-off-by: T.J. Alumbaugh <talumbau@xxxxxxxxxx>
---
Documentation/mm/multigen_lru.rst | 33 +++-
include/linux/mm_inline.h | 17 --
include/linux/mmzone.h | 13 +-
mm/memcontrol.c | 8 +-
mm/vmscan.c | 250 +++++++++++++++++-------------
5 files changed, 178 insertions(+), 143 deletions(-)
diff --git a/Documentation/mm/multigen_lru.rst b/Documentation/mm/multigen_lru.rst
index 770b5d539856..5f1f6ecbb79b 100644
--- a/Documentation/mm/multigen_lru.rst
+++ b/Documentation/mm/multigen_lru.rst
@@ -186,9 +186,40 @@ is false positive, the cost is an additional scan of a range of PTEs,
which may yield hot pages anyway. Parameters of the filter itself can
control the false positive rate in the limit.
+Memcg LRU
+---------
+An memcg LRU is a per-node LRU of memcgs. It is also an LRU of LRUs,
+since each node and memcg combination has an LRU of folios (see
+``mem_cgroup_lruvec()``). Its goal is to improve the scalability of
+global reclaim, which is critical to system-wide memory overcommit in
+data centers. Note that memcg LRU only applies to global reclaim.
+
+The basic structure of an memcg LRU can be understood by an analogy to
+the active/inactive LRU (of folios):
+
+1. It has the young and the old (generations), i.e., the counterparts
+ to the active and the inactive;
+2. The increment of ``max_seq`` triggers promotion, i.e., the
+ counterpart to activation;
+3. Other events trigger similar operations, e.g., offlining an memcg
+ triggers demotion, i.e., the counterpart to deactivation.
+
+In terms of global reclaim, it has two distinct features:
+
+1. Sharding, which allows each thread to start at a random memcg (in
+ the old generation) and improves parallelism;
+2. Eventual fairness, which allows direct reclaim to bail out at will
+ and reduces latency without affecting fairness over some time.
+
+In terms of traversing memcgs during global reclaim, it improves the
+best-case complexity from O(n) to O(1) and does not affect the
+worst-case complexity O(n). Therefore, on average, it has a sublinear
+complexity.
+
Summary
-------
-The multi-gen LRU can be disassembled into the following parts:
+The multi-gen LRU (of folios) can be disassembled into the following
+parts:
* Generations
* Rmap walks
diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
index 26dcbda07e92..de1e622dd366 100644
--- a/include/linux/mm_inline.h
+++ b/include/linux/mm_inline.h
@@ -122,18 +122,6 @@ static inline bool lru_gen_in_fault(void)
return current->in_lru_fault;
}
-#ifdef CONFIG_MEMCG
-static inline int lru_gen_memcg_seg(struct lruvec *lruvec)
-{
- return READ_ONCE(lruvec->lrugen.seg);
-}
-#else
-static inline int lru_gen_memcg_seg(struct lruvec *lruvec)
-{
- return 0;
-}
-#endif
-
static inline int lru_gen_from_seq(unsigned long seq)
{
return seq % MAX_NR_GENS;
@@ -309,11 +297,6 @@ static inline bool lru_gen_in_fault(void)
return false;
}
-static inline int lru_gen_memcg_seg(struct lruvec *lruvec)
-{
- return 0;
-}
-
static inline bool lru_gen_add_folio(struct lruvec *lruvec, struct folio *folio, bool reclaiming)
{
return false;
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index ae7d4e92c12d..c54964979ccf 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -368,15 +368,6 @@ struct page_vma_mapped_walk;
#define LRU_GEN_MASK ((BIT(LRU_GEN_WIDTH) - 1) << LRU_GEN_PGOFF)
#define LRU_REFS_MASK ((BIT(LRU_REFS_WIDTH) - 1) << LRU_REFS_PGOFF)
-/* see the comment on MEMCG_NR_GENS */
-enum {
- MEMCG_LRU_NOP,
- MEMCG_LRU_HEAD,
- MEMCG_LRU_TAIL,
- MEMCG_LRU_OLD,
- MEMCG_LRU_YOUNG,
-};
-
#ifdef CONFIG_LRU_GEN
enum {
@@ -557,7 +548,7 @@ void lru_gen_exit_memcg(struct mem_cgroup *memcg);
void lru_gen_online_memcg(struct mem_cgroup *memcg);
void lru_gen_offline_memcg(struct mem_cgroup *memcg);
void lru_gen_release_memcg(struct mem_cgroup *memcg);
-void lru_gen_rotate_memcg(struct lruvec *lruvec, int op);
+void lru_gen_soft_reclaim(struct lruvec *lruvec);
#else /* !CONFIG_MEMCG */
@@ -608,7 +599,7 @@ static inline void lru_gen_release_memcg(struct mem_cgroup *memcg)
{
}
-static inline void lru_gen_rotate_memcg(struct lruvec *lruvec, int op)
+static inline void lru_gen_soft_reclaim(struct lruvec *lruvec)
{
}
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 893427aded01..17335459d8dc 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -476,12 +476,8 @@ static void mem_cgroup_update_tree(struct mem_cgroup *memcg, int nid)
struct mem_cgroup_tree_per_node *mctz;
if (lru_gen_enabled()) {
- struct lruvec *lruvec = &memcg->nodeinfo[nid]->lruvec;
-
- /* see the comment on MEMCG_NR_GENS */
- if (soft_limit_excess(memcg) && lru_gen_memcg_seg(lruvec) != MEMCG_LRU_HEAD)
- lru_gen_rotate_memcg(lruvec, MEMCG_LRU_HEAD);
-
+ if (soft_limit_excess(memcg))
+ lru_gen_soft_reclaim(&memcg->nodeinfo[nid]->lruvec);
return;
}
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 1be9120349f8..796d4ca65e97 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4705,6 +4705,148 @@ void lru_gen_look_around(struct page_vma_mapped_walk *pvmw)
mem_cgroup_unlock_pages();
}
+/******************************************************************************
+ * memcg LRU
+ ******************************************************************************/
+
+/* see the comment on MEMCG_NR_GENS */
+enum {
+ MEMCG_LRU_NOP,
+ MEMCG_LRU_HEAD,
+ MEMCG_LRU_TAIL,
+ MEMCG_LRU_OLD,
+ MEMCG_LRU_YOUNG,
+};
+
+#ifdef CONFIG_MEMCG
+
+static int lru_gen_memcg_seg(struct lruvec *lruvec)
+{
+ return READ_ONCE(lruvec->lrugen.seg);
+}
+
+static void lru_gen_rotate_memcg(struct lruvec *lruvec, int op)
+{
+ int seg;
+ int old, new;
+ int bin = get_random_u32_below(MEMCG_NR_BINS);
+ struct pglist_data *pgdat = lruvec_pgdat(lruvec);
+
+ spin_lock(&pgdat->memcg_lru.lock);
+
+ VM_WARN_ON_ONCE(hlist_nulls_unhashed(&lruvec->lrugen.list));
+
+ seg = 0;
+ new = old = lruvec->lrugen.gen;
+
+ /* see the comment on MEMCG_NR_GENS */
+ if (op == MEMCG_LRU_HEAD)
+ seg = MEMCG_LRU_HEAD;
+ else if (op == MEMCG_LRU_TAIL)
+ seg = MEMCG_LRU_TAIL;
+ else if (op == MEMCG_LRU_OLD)
+ new = get_memcg_gen(pgdat->memcg_lru.seq);
+ else if (op == MEMCG_LRU_YOUNG)
+ new = get_memcg_gen(pgdat->memcg_lru.seq + 1);
+ else
+ VM_WARN_ON_ONCE(true);
+
+ hlist_nulls_del_rcu(&lruvec->lrugen.list);
+
+ if (op == MEMCG_LRU_HEAD || op == MEMCG_LRU_OLD)
+ hlist_nulls_add_head_rcu(&lruvec->lrugen.list, &pgdat->memcg_lru.fifo[new][bin]);
+ else
+ hlist_nulls_add_tail_rcu(&lruvec->lrugen.list, &pgdat->memcg_lru.fifo[new][bin]);
+
+ pgdat->memcg_lru.nr_memcgs[old]--;
+ pgdat->memcg_lru.nr_memcgs[new]++;
+
+ lruvec->lrugen.gen = new;
+ WRITE_ONCE(lruvec->lrugen.seg, seg);
+
+ if (!pgdat->memcg_lru.nr_memcgs[old] && old == get_memcg_gen(pgdat->memcg_lru.seq))
+ WRITE_ONCE(pgdat->memcg_lru.seq, pgdat->memcg_lru.seq + 1);
+
+ spin_unlock(&pgdat->memcg_lru.lock);
+}
+
+void lru_gen_online_memcg(struct mem_cgroup *memcg)
+{
+ int gen;
+ int nid;
+ int bin = get_random_u32_below(MEMCG_NR_BINS);
+
+ for_each_node(nid) {
+ struct pglist_data *pgdat = NODE_DATA(nid);
+ struct lruvec *lruvec = get_lruvec(memcg, nid);
+
+ spin_lock(&pgdat->memcg_lru.lock);
+
+ VM_WARN_ON_ONCE(!hlist_nulls_unhashed(&lruvec->lrugen.list));
+
+ gen = get_memcg_gen(pgdat->memcg_lru.seq);
+
+ hlist_nulls_add_tail_rcu(&lruvec->lrugen.list, &pgdat->memcg_lru.fifo[gen][bin]);
+ pgdat->memcg_lru.nr_memcgs[gen]++;
+
+ lruvec->lrugen.gen = gen;
+
+ spin_unlock(&pgdat->memcg_lru.lock);
+ }
+}
+
+void lru_gen_offline_memcg(struct mem_cgroup *memcg)
+{
+ int nid;
+
+ for_each_node(nid) {
+ struct lruvec *lruvec = get_lruvec(memcg, nid);
+
+ lru_gen_rotate_memcg(lruvec, MEMCG_LRU_OLD);
+ }
+}
+
+void lru_gen_release_memcg(struct mem_cgroup *memcg)
+{
+ int gen;
+ int nid;
+
+ for_each_node(nid) {
+ struct pglist_data *pgdat = NODE_DATA(nid);
+ struct lruvec *lruvec = get_lruvec(memcg, nid);
+
+ spin_lock(&pgdat->memcg_lru.lock);
+
+ VM_WARN_ON_ONCE(hlist_nulls_unhashed(&lruvec->lrugen.list));
+
+ gen = lruvec->lrugen.gen;
+
+ hlist_nulls_del_rcu(&lruvec->lrugen.list);
+ pgdat->memcg_lru.nr_memcgs[gen]--;
+
+ if (!pgdat->memcg_lru.nr_memcgs[gen] && gen == get_memcg_gen(pgdat->memcg_lru.seq))
+ WRITE_ONCE(pgdat->memcg_lru.seq, pgdat->memcg_lru.seq + 1);
+
+ spin_unlock(&pgdat->memcg_lru.lock);
+ }
+}
+
+void lru_gen_soft_reclaim(struct lruvec *lruvec)
+{
+ /* see the comment on MEMCG_NR_GENS */
+ if (lru_gen_memcg_seg(lruvec) != MEMCG_LRU_HEAD)
+ lru_gen_rotate_memcg(lruvec, MEMCG_LRU_HEAD);
+}
+
+#else /* !CONFIG_MEMCG */
+
+static int lru_gen_memcg_seg(struct lruvec *lruvec)
+{
+ return 0;
+}
+
+#endif
+
/******************************************************************************
* the eviction
******************************************************************************/
@@ -5397,53 +5539,6 @@ static void lru_gen_shrink_node(struct pglist_data *pgdat, struct scan_control *
pgdat->kswapd_failures = 0;
}
-#ifdef CONFIG_MEMCG
-void lru_gen_rotate_memcg(struct lruvec *lruvec, int op)
-{
- int seg;
- int old, new;
- int bin = get_random_u32_below(MEMCG_NR_BINS);
- struct pglist_data *pgdat = lruvec_pgdat(lruvec);
-
- spin_lock(&pgdat->memcg_lru.lock);
-
- VM_WARN_ON_ONCE(hlist_nulls_unhashed(&lruvec->lrugen.list));
-
- seg = 0;
- new = old = lruvec->lrugen.gen;
-
- /* see the comment on MEMCG_NR_GENS */
- if (op == MEMCG_LRU_HEAD)
- seg = MEMCG_LRU_HEAD;
- else if (op == MEMCG_LRU_TAIL)
- seg = MEMCG_LRU_TAIL;
- else if (op == MEMCG_LRU_OLD)
- new = get_memcg_gen(pgdat->memcg_lru.seq);
- else if (op == MEMCG_LRU_YOUNG)
- new = get_memcg_gen(pgdat->memcg_lru.seq + 1);
- else
- VM_WARN_ON_ONCE(true);
-
- hlist_nulls_del_rcu(&lruvec->lrugen.list);
-
- if (op == MEMCG_LRU_HEAD || op == MEMCG_LRU_OLD)
- hlist_nulls_add_head_rcu(&lruvec->lrugen.list, &pgdat->memcg_lru.fifo[new][bin]);
- else
- hlist_nulls_add_tail_rcu(&lruvec->lrugen.list, &pgdat->memcg_lru.fifo[new][bin]);
-
- pgdat->memcg_lru.nr_memcgs[old]--;
- pgdat->memcg_lru.nr_memcgs[new]++;
-
- lruvec->lrugen.gen = new;
- WRITE_ONCE(lruvec->lrugen.seg, seg);
-
- if (!pgdat->memcg_lru.nr_memcgs[old] && old == get_memcg_gen(pgdat->memcg_lru.seq))
- WRITE_ONCE(pgdat->memcg_lru.seq, pgdat->memcg_lru.seq + 1);
-
- spin_unlock(&pgdat->memcg_lru.lock);
-}
-#endif
-
/******************************************************************************
* state change
******************************************************************************/
@@ -6086,67 +6181,6 @@ void lru_gen_exit_memcg(struct mem_cgroup *memcg)
}
}
-void lru_gen_online_memcg(struct mem_cgroup *memcg)
-{
- int gen;
- int nid;
- int bin = get_random_u32_below(MEMCG_NR_BINS);
-
- for_each_node(nid) {
- struct pglist_data *pgdat = NODE_DATA(nid);
- struct lruvec *lruvec = get_lruvec(memcg, nid);
-
- spin_lock(&pgdat->memcg_lru.lock);
-
- VM_WARN_ON_ONCE(!hlist_nulls_unhashed(&lruvec->lrugen.list));
-
- gen = get_memcg_gen(pgdat->memcg_lru.seq);
-
- hlist_nulls_add_tail_rcu(&lruvec->lrugen.list, &pgdat->memcg_lru.fifo[gen][bin]);
- pgdat->memcg_lru.nr_memcgs[gen]++;
-
- lruvec->lrugen.gen = gen;
-
- spin_unlock(&pgdat->memcg_lru.lock);
- }
-}
-
-void lru_gen_offline_memcg(struct mem_cgroup *memcg)
-{
- int nid;
-
- for_each_node(nid) {
- struct lruvec *lruvec = get_lruvec(memcg, nid);
-
- lru_gen_rotate_memcg(lruvec, MEMCG_LRU_OLD);
- }
-}
-
-void lru_gen_release_memcg(struct mem_cgroup *memcg)
-{
- int gen;
- int nid;
-
- for_each_node(nid) {
- struct pglist_data *pgdat = NODE_DATA(nid);
- struct lruvec *lruvec = get_lruvec(memcg, nid);
-
- spin_lock(&pgdat->memcg_lru.lock);
-
- VM_WARN_ON_ONCE(hlist_nulls_unhashed(&lruvec->lrugen.list));
-
- gen = lruvec->lrugen.gen;
-
- hlist_nulls_del_rcu(&lruvec->lrugen.list);
- pgdat->memcg_lru.nr_memcgs[gen]--;
-
- if (!pgdat->memcg_lru.nr_memcgs[gen] && gen == get_memcg_gen(pgdat->memcg_lru.seq))
- WRITE_ONCE(pgdat->memcg_lru.seq, pgdat->memcg_lru.seq + 1);
-
- spin_unlock(&pgdat->memcg_lru.lock);
- }
-}
-
#endif /* CONFIG_MEMCG */
static int __init init_lru_gen(void)
--
2.39.0.314.g84b9a713c41-goog