[PATCH 1/3] mm: page_counter: add page_counter_protection struct and init API

[linuszeng via B4 Relay]

From: linuszeng <linuszeng@xxxxxxxxxxx>

Hierarchical protection (memory.min/memory.low) is only used by the
memory page counter (and dmem pools); swap/memsw, kmem and tcpmem
counters never participate in it, yet each struct page_counter carries
the full protection state.

Introduce struct page_counter_protection to hold that state, link it to
struct page_counter via a ->prot pointer (NULL when protection is not
supported) and switch track_protection() to it. page_counter_init()
drops its protection_support argument and the new
page_counter_init_protection() attaches the protection context. Like
page_counter_init(), it expects the rest of the structure to be zeroed
by the caller's allocation.

Protection tracking is only enabled on the cgroup v2 hierarchy, matching
the previous page_counter_init(..., memcg_on_dfl) behavior.

No functional change.
---
 include/linux/memcontrol.h   |  7 ++++++
 include/linux/page_counter.h | 59 +++++++++++++++++++++++++++++++++++++++-----
 kernel/cgroup/dmem.c         |  6 +++--
 mm/hugetlb_cgroup.c          |  4 +--
 mm/memcontrol.c              | 21 ++++++++++------
 mm/page_counter.c            |  2 +-
 6 files changed, 80 insertions(+), 19 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index 058ebd73ff16..ed863f4ed233 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -195,6 +195,13 @@ struct mem_cgroup {
 	/* Accounted resources */
 	struct page_counter memory;		/* Both v1 & v2 */
 
+	/*
+	 * Hierarchical memory.min/memory.low protection tracking for the
+	 * memory page counter. swap/memsw, kmem and tcpmem counters do not
+	 * support protection and have no such context.
+	 */
+	struct page_counter_protection memory_prot;
+
 	union {
 		struct page_counter swap;	/* v2 only */
 		struct page_counter memsw;	/* v1 only */
diff --git a/include/linux/page_counter.h b/include/linux/page_counter.h
index 07b7cb12249c..b81f16702764 100644
--- a/include/linux/page_counter.h
+++ b/include/linux/page_counter.h
@@ -7,6 +7,32 @@
 #include <linux/limits.h>
 #include <asm/page.h>
 
+/*
+ * Hierarchical protection (memory.min / memory.low) tracking.
+ *
+ * Only the memory page counter (and dmem pools) participate in protection.
+ * swap/memsw, kmem and tcpmem page counters never do, so the protection
+ * fields are kept out of struct page_counter in this separate structure to
+ * save space in the common case. struct page_counter links to it via ->prot,
+ * which is NULL for counters without protection support.
+ */
+struct page_counter_protection {
+	struct page_counter_protection *parent;
+
+	/* effective memory.min and memory.min usage tracking */
+	unsigned long emin;
+	atomic_long_t min_usage;
+	atomic_long_t children_min_usage;
+
+	/* effective memory.low and memory.low usage tracking */
+	unsigned long elow;
+	atomic_long_t low_usage;
+	atomic_long_t children_low_usage;
+
+	unsigned long min;
+	unsigned long low;
+};
+
 struct page_counter {
 	/*
 	 * Make sure 'usage' does not share cacheline with any other field in
@@ -41,6 +67,12 @@ struct page_counter {
 	unsigned long high;
 	unsigned long max;
 	struct page_counter *parent;
+
+	/*
+	 * Hierarchical protection context, NULL for counters that do not
+	 * support memory.min/memory.low (swap, memsw, kmem, tcpmem, ...).
+	 */
+	struct page_counter_protection *prot;
 } ____cacheline_internodealigned_in_smp;
 
 #if BITS_PER_LONG == 32
@@ -49,18 +81,33 @@ struct page_counter {
 #define PAGE_COUNTER_MAX (LONG_MAX / PAGE_SIZE)
 #endif
 
-/*
- * Protection is supported only for the first counter (with id 0).
- */
 static inline void page_counter_init(struct page_counter *counter,
-				     struct page_counter *parent,
-				     bool protection_support)
+				     struct page_counter *parent)
 {
 	counter->usage = (atomic_long_t)ATOMIC_LONG_INIT(0);
 	counter->max = PAGE_COUNTER_MAX;
 	counter->parent = parent;
-	counter->protection_support = protection_support;
 	counter->track_failcnt = false;
+	counter->prot = NULL;
+}
+
+/*
+ * Enable hierarchical protection (memory.min/memory.low) on @counter.
+ * @prot and @parent are the protection contexts of @counter and its
+ * parent page counter respectively. Only the memory page counter (and
+ * dmem pools) call this.
+ *
+ * The remaining members of @prot (emin, elow and the usage counters) are
+ * expected to be zero already, so @prot must come from zeroed memory.
+ */
+static inline void page_counter_init_protection(struct page_counter *counter,
+						struct page_counter_protection *prot,
+						struct page_counter_protection *parent)
+{
+	counter->prot = prot;
+	prot->parent = parent;
+	prot->min = 0;
+	prot->low = 0;
 }
 
 static inline unsigned long page_counter_read(struct page_counter *counter)
diff --git a/kernel/cgroup/dmem.c b/kernel/cgroup/dmem.c
index 4683f3d68022..e33d807cdea8 100644
--- a/kernel/cgroup/dmem.c
+++ b/kernel/cgroup/dmem.c
@@ -88,6 +88,7 @@ struct dmem_cgroup_pool_state {
 	struct rcu_head rcu;
 
 	struct page_counter cnt;
+	struct page_counter_protection prot;
 	struct dmem_cgroup_pool_state *parent;
 
 	refcount_t ref;
@@ -426,8 +427,9 @@ alloc_pool_single(struct dmemcg_state *dmemcs, struct dmem_cgroup_region *region
 	if (parent)
 		ppool = find_cg_pool_locked(parent, region);
 
-	page_counter_init(&pool->cnt,
-			  ppool ? &ppool->cnt : NULL, true);
+	page_counter_init(&pool->cnt, ppool ? &ppool->cnt : NULL);
+	page_counter_init_protection(&pool->cnt, &pool->prot,
+				     ppool ? &ppool->prot : NULL);
 	reset_all_resource_limits(pool);
 	refcount_set(&pool->ref, 1);
 	kref_get(&region->ref);
diff --git a/mm/hugetlb_cgroup.c b/mm/hugetlb_cgroup.c
index ecb6e0b7819a..7fdae504cfc6 100644
--- a/mm/hugetlb_cgroup.c
+++ b/mm/hugetlb_cgroup.c
@@ -108,8 +108,8 @@ static void hugetlb_cgroup_init(struct hugetlb_cgroup *h_cgroup,
 		fault = hugetlb_cgroup_counter_from_cgroup(h_cgroup, idx);
 		rsvd = hugetlb_cgroup_counter_from_cgroup_rsvd(h_cgroup, idx);
 
-		page_counter_init(fault, fault_parent, false);
-		page_counter_init(rsvd, rsvd_parent, false);
+		page_counter_init(fault, fault_parent);
+		page_counter_init(rsvd, rsvd_parent);
 
 		if (!cgroup_subsys_on_dfl(hugetlb_cgrp_subsys)) {
 			fault->track_failcnt = true;
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 86ff580c7018..ffa1ced3baae 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -4267,25 +4267,30 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
 #endif
 	page_counter_set_high(&memcg->swap, PAGE_COUNTER_MAX);
 	if (parent) {
-		page_counter_init(&memcg->memory, &parent->memory, memcg_on_dfl);
-		page_counter_init(&memcg->swap, &parent->swap, false);
+		page_counter_init(&memcg->memory, &parent->memory);
+		if (memcg_on_dfl)
+			page_counter_init_protection(&memcg->memory, &memcg->memory_prot,
+						     &parent->memory_prot);
+		page_counter_init(&memcg->swap, &parent->swap);
 #ifdef CONFIG_MEMCG_V1
 		WRITE_ONCE(memcg->swappiness, mem_cgroup_swappiness(parent));
 		memcg->memory.track_failcnt = !memcg_on_dfl;
 		memcg->memsw.track_failcnt = !memcg_on_dfl;
 		WRITE_ONCE(memcg->oom_kill_disable, READ_ONCE(parent->oom_kill_disable));
-		page_counter_init(&memcg->kmem, &parent->kmem, false);
-		page_counter_init(&memcg->tcpmem, &parent->tcpmem, false);
+		page_counter_init(&memcg->kmem, &parent->kmem);
+		page_counter_init(&memcg->tcpmem, &parent->tcpmem);
 		memcg->tcpmem.track_failcnt = !memcg_on_dfl;
 #endif
 	} else {
 		init_memcg_stats();
 		init_memcg_events();
-		page_counter_init(&memcg->memory, NULL, true);
-		page_counter_init(&memcg->swap, NULL, false);
+		page_counter_init(&memcg->memory, NULL);
+		page_counter_init_protection(&memcg->memory, &memcg->memory_prot,
+					     NULL);
+		page_counter_init(&memcg->swap, NULL);
 #ifdef CONFIG_MEMCG_V1
-		page_counter_init(&memcg->kmem, NULL, false);
-		page_counter_init(&memcg->tcpmem, NULL, false);
+		page_counter_init(&memcg->kmem, NULL);
+		page_counter_init(&memcg->tcpmem, NULL);
 #endif
 		root_mem_cgroup = memcg;
 		return &memcg->css;
diff --git a/mm/page_counter.c b/mm/page_counter.c
index 450543f4b318..38cb99f5f50e 100644
--- a/mm/page_counter.c
+++ b/mm/page_counter.c
@@ -15,7 +15,7 @@
 
 static bool track_protection(struct page_counter *c)
 {
-	return c->protection_support;
+	return c->prot != NULL;
 }
 
 static void propagate_protected_usage(struct page_counter *c,

-- 
2.43.7