[RFC PATCH 09/14] mm/slub: add the slab freelists to kmem_cache

[Matteo Rizzo]

From: Jann Horn <jannh@xxxxxxxxxx>

With SLAB_VIRTUAL enabled, unused slabs which still have virtual memory
allocated to them but no physical memory are kept in a per-cache list so
that they can be reused later if the cache needs to grow again.

Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>
Co-developed-by: Matteo Rizzo <matteorizzo@xxxxxxxxxx>
Signed-off-by: Matteo Rizzo <matteorizzo@xxxxxxxxxx>
---
 include/linux/slub_def.h | 16 ++++++++++++++++
 mm/slub.c                | 23 +++++++++++++++++++++++
 2 files changed, 39 insertions(+)

diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
index 0adf5ba8241b..693e9bb34edc 100644
--- a/include/linux/slub_def.h
+++ b/include/linux/slub_def.h
@@ -86,6 +86,20 @@ struct kmem_cache_cpu {
 /*
  * Slab cache management.
  */
+struct kmem_cache_virtual {
+#ifdef CONFIG_SLAB_VIRTUAL
+	/* Protects freed_slabs and freed_slabs_min */
+	spinlock_t freed_slabs_lock;
+	/*
+	 * Slabs on this list have virtual memory of size oo allocated to them
+	 * but no physical memory
+	 */
+	struct list_head freed_slabs;
+	/* Same as freed_slabs but with memory of size min */
+	struct list_head freed_slabs_min;
+#endif
+};
+
 struct kmem_cache {
 #ifndef CONFIG_SLUB_TINY
 	struct kmem_cache_cpu __percpu *cpu_slab;
@@ -107,6 +121,8 @@ struct kmem_cache {
 
 	/* Allocation and freeing of slabs */
 	struct kmem_cache_order_objects min;
+	struct kmem_cache_virtual virtual;
+
 	gfp_t allocflags;	/* gfp flags to use on each alloc */
 	int refcount;		/* Refcount for slab cache destroy */
 	void (*ctor)(void *);
diff --git a/mm/slub.c b/mm/slub.c
index 42e7cc0b4452..4f77e5d4fe6c 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -4510,8 +4510,20 @@ static int calculate_sizes(struct kmem_cache *s)
 	return !!oo_objects(s->oo);
 }
 
+static inline void slab_virtual_open(struct kmem_cache *s)
+{
+#ifdef CONFIG_SLAB_VIRTUAL
+	/* WARNING: this stuff will be relocated in bootstrap()! */
+	spin_lock_init(&s->virtual.freed_slabs_lock);
+	INIT_LIST_HEAD(&s->virtual.freed_slabs);
+	INIT_LIST_HEAD(&s->virtual.freed_slabs_min);
+#endif
+}
+
 static int kmem_cache_open(struct kmem_cache *s, slab_flags_t flags)
 {
+	slab_virtual_open(s);
+
 	s->flags = kmem_cache_flags(s->size, flags, s->name);
 #ifdef CONFIG_SLAB_FREELIST_HARDENED
 	s->random = get_random_long();
@@ -4994,6 +5006,16 @@ static int slab_memory_callback(struct notifier_block *self,
  * that may be pointing to the wrong kmem_cache structure.
  */
 
+static inline void slab_virtual_bootstrap(struct kmem_cache *s, struct kmem_cache *static_cache)
+{
+	slab_virtual_open(s);
+
+#ifdef CONFIG_SLAB_VIRTUAL
+	list_splice(&static_cache->virtual.freed_slabs, &s->virtual.freed_slabs);
+	list_splice(&static_cache->virtual.freed_slabs_min, &s->virtual.freed_slabs_min);
+#endif
+}
+
 static struct kmem_cache * __init bootstrap(struct kmem_cache *static_cache)
 {
 	int node;
@@ -5001,6 +5023,7 @@ static struct kmem_cache * __init bootstrap(struct kmem_cache *static_cache)
 	struct kmem_cache_node *n;
 
 	memcpy(s, static_cache, kmem_cache->object_size);
+	slab_virtual_bootstrap(s, static_cache);
 
 	/*
 	 * This runs very early, and only the boot processor is supposed to be
-- 
2.42.0.459.ge4e396fd5e-goog