Document percpu alloc

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I8fa4b68e8a68c57da8ab726d0f68ee12aad2f15e

2 files changed, 204 insertions, 4 deletions

diff --git a/include/rseq/percpu-alloc.h b/include/rseq/percpu-alloc.h
index 2776b67..0761acc 100644
--- a/include/rseq/percpu-alloc.h
+++ b/include/rseq/percpu-alloc.h
@@ -9,13 +9,23 @@
 #include <sys/mman.h>
 
 /*
- * rseq/percpu-alloc.h
+ * rseq/percpu-alloc.h: rseq CPU-Local Storage (CLS) memory allocator.
+ *
+ * The rseq per-CPU memory allocator allows the application the request
+ * memory pools of CPU-Local memory each of containing objects of a
+ * given size (rounded to next power of 2), reserving a given virtual
+ * address size per CPU, for a given maximum number of CPUs.
+ *
+ * The per-CPU memory allocator is analogous to TLS (Thread-Local
+ * Storage) memory: TLS is Thread-Local Storage, whereas the per-CPU
+ * memory allocator provides CPU-Local Storage.
  */
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
+
 /*
  * Tag pointers returned by:
  * - rseq_percpu_malloc(),
@@ -23,32 +33,222 @@ extern "C" {
  * - rseq_percpu_pool_set_malloc(),
  * - rseq_percpu_pool_set_zmalloc().
  *
+ * and passed as parameter to:
+ * - rseq_percpu_ptr(),
+ * - rseq_percpu_free().
+ *
  * with __rseq_percpu for use by static analyzers.
  */
 #define __rseq_percpu
 
 struct rseq_percpu_pool;
 
+/*
+ * rseq_percpu_pool_create: Create a per-cpu memory pool.
+ *
+ * Create a per-cpu memory pool for items of size @item_len (rounded to
+ * next power of two). The reserved allocation size is @percpu_len, and
+ * the maximum CPU value expected is (@max_nr_cpus - 1).
+ *
+ * Arguments @mmap_prot, @mmap_flags, @mmap_fd, @mmap_offset are passed
+ * as arguments to mmap(2) when allocating the memory area holding the
+ * percpu pool.
+ *
+ * Argument @numa_flags are passed to move_pages(2). The expected flags
+ * are:
+ *   0:                do not move pages to specific numa nodes
+ *                     (use for e.g. mm_cid indexing).
+ *   MPOL_MF_MOVE:     move process-private pages to cpu-specific numa nodes.
+ *   MPOL_MF_MOVE_ALL: move shared pages to cpu-specific numa nodes
+ *                     (requires CAP_SYS_NICE).
+ *
+ * Returns a pointer to the created percpu pool. Return NULL on error,
+ * with errno set accordingly:
+ *   EINVAL: Invalid argument.
+ *   ENOMEM: Not enough resources (memory or pool indexes) available to
+ *           allocate pool.
+ *
+ * In addition, if mmap(2) fails, NULL is returned and errno is
+ * propagated from mmap(2).
+ *
+ * This API is MT-safe.
+ */
 struct rseq_percpu_pool *rseq_percpu_pool_create(size_t item_len,
 		size_t percpu_len, int max_nr_cpus,
 		int mmap_prot, int mmap_flags, int mmap_fd, off_t mmap_offset,
 		int numa_flags);
+
+/*
+ * rseq_percpu_pool_destroy: Destroy a per-cpu memory pool.
+ *
+ * Destroy a per-cpu memory pool, unmapping its memory and removing the
+ * pool entry from the global index. No pointers allocated from the
+ * pool should be used when it is destroyed. This includes rseq_percpu_ptr().
+ *
+ * Argument @pool is a pointer to the per-cpu pool to destroy.
+ *
+ * Return values: 0 on success, -1 on error, with errno set accordingly:
+ *   ENOENT: Trying to free a pool which was not allocated.
+ *
+ * If munmap(2) fails, -1 is returned and errno is propagated from
+ * munmap(2).
+ *
+ * This API is MT-safe.
+ */
 int rseq_percpu_pool_destroy(struct rseq_percpu_pool *pool);
 
+/*
+ * rseq_percpu_malloc: Allocate memory from a per-cpu pool.
+ *
+ * Allocate an item from a per-cpu @pool. The allocation will reserve
+ * an item of the size specified by @item_len (rounded to next power of
+ * two) at pool creation. This effectively reserves space for this item
+ * on all CPUs.
+ *
+ * On success, return a "__rseq_percpu" encoded pointer to the pool
+ * item. This encoded pointer is meant to be passed to rseq_percpu_ptr()
+ * to be decoded to a valid address before being accessed.
+ *
+ * Return NULL (errno=ENOMEM) if there is not enough space left in the
+ * pool to allocate an item.
+ *
+ * This API is MT-safe.
+ */
 void __rseq_percpu *rseq_percpu_malloc(struct rseq_percpu_pool *pool);
+
+/*
+ * rseq_percpu_zmalloc: Allocated zero-initialized memory from a per-cpu pool.
+ *
+ * Allocate memory for an item within the pool, and zero-initialize its
+ * memory on all CPUs. See rseq_percpu_malloc for details.
+ *
+ * This API is MT-safe.
+ */
 void __rseq_percpu *rseq_percpu_zmalloc(struct rseq_percpu_pool *pool);
+
+/*
+ * rseq_percpu_free: Free memory from a per-cpu pool.
+ *
+ * Free an item pointed to by @ptr from its per-cpu pool.
+ *
+ * The @ptr argument is a __rseq_percpu encoded pointer returned by
+ * either:
+ *
+ * - rseq_percpu_malloc(),
+ * - rseq_percpu_zmalloc(),
+ * - rseq_percpu_pool_set_malloc(),
+ * - rseq_percpu_pool_set_zmalloc().
+ *
+ * This API is MT-safe.
+ */
 void rseq_percpu_free(void __rseq_percpu *ptr);
 
+/*
+ * rseq_percpu_ptr: Decode a per-cpu pointer.
+ *
+ * Decode a per-cpu pointer @ptr to get the associated pointer for the
+ * given @cpu. The @ptr argument is a __rseq_percpu encoded pointer
+ * returned by either:
+ *
+ * - rseq_percpu_malloc(),
+ * - rseq_percpu_zmalloc(),
+ * - rseq_percpu_pool_set_malloc(),
+ * - rseq_percpu_pool_set_zmalloc().
+ *
+ * The __rseq_percpu pointer can be decoded with rseq_percpu_ptr() even
+ * after it has been freed, as long as its associated pool has not been
+ * destroyed. However, memory pointed to by the decoded pointer should
+ * not be accessed after the __rseq_percpu pointer has been freed.
+ *
+ * The macro rseq_percpu_ptr() preserves the type of the @ptr parameter
+ * for the returned pointer, but removes the __rseq_percpu annotation.
+ *
+ * This API is MT-safe.
+ */
 void *__rseq_percpu_ptr(void __rseq_percpu *ptr, int cpu);
-
 #define rseq_percpu_ptr(ptr, cpu)	((__typeof__(*(ptr)) *) __rseq_percpu_ptr(ptr, cpu))
 
+/*
+ * rseq_percpu_pool_set_create: Create a pool set.
+ *
+ * Create a set of pools. Its purpose is to offer a memory allocator API
+ * for variable-length items (e.g. variable length strings). When
+ * created, the pool set has no pool. Pools can be created and added to
+ * the set. One common approach would be to create pools for each
+ * relevant power of two allocation size useful for the application.
+ * Only one pool can be added to the pool set for each power of two
+ * allocation size.
+ *
+ * Returns a pool set pointer on success, else returns NULL with
+ * errno=ENOMEM (out of memory).
+ *
+ * This API is MT-safe.
+ */
 struct rseq_percpu_pool_set *rseq_percpu_pool_set_create(void);
+
+/*
+ * rseq_percpu_pool_set_destroy: Destroy a pool set.
+ *
+ * Destroy a pool set and its associated resources. The pools that were
+ * added to the pool set are destroyed as well.
+ *
+ * Returns 0 on success, -1 on failure (or partial failure), with errno
+ * set by rseq_percpu_pool_destroy(). Using a pool set after destroy
+ * failure is undefined.
+ *
+ * This API is MT-safe.
+ */
 int rseq_percpu_pool_set_destroy(struct rseq_percpu_pool_set *pool_set);
+
+/*
+ * rseq_percpu_pool_set_add_pool: Add a pool to a pool set.
+ *
+ * Add a @pool to the @pool_set. On success, its ownership is handed
+ * over to the pool set, so the caller should not destroy it explicitly.
+ * Only one pool can be added to the pool set for each power of two
+ * allocation size.
+ *
+ * Returns 0 on success, -1 on error with the following errno:
+ * - EBUSY: A pool already exists in the pool set for this power of two
+ *          allocation size.
+ *
+ * This API is MT-safe.
+ */
 int rseq_percpu_pool_set_add_pool(struct rseq_percpu_pool_set *pool_set,
 		struct rseq_percpu_pool *pool);
 
+/*
+ * rseq_percpu_pool_set_malloc: Allocate memory from a per-cpu pool set.
+ *
+ * Allocate an item from a per-cpu @pool. The allocation will reserve
+ * an item of the size specified by @len (rounded to next power of
+ * two). This effectively reserves space for this item on all CPUs.
+ *
+ * The space reservation will search for the smallest pool within
+ * @pool_set which respects the following conditions:
+ *
+ * - it has an item size large enough to fit @len,
+ * - it has space available.
+ *
+ * On success, return a "__rseq_percpu" encoded pointer to the pool
+ * item. This encoded pointer is meant to be passed to rseq_percpu_ptr()
+ * to be decoded to a valid address before being accessed.
+ *
+ * Return NULL (errno=ENOMEM) if there is not enough space left in the
+ * pool to allocate an item.
+ *
+ * This API is MT-safe.
+ */
 void __rseq_percpu *rseq_percpu_pool_set_malloc(struct rseq_percpu_pool_set *pool_set, size_t len);
+
+/*
+ * rseq_percpu_pool_set_zmalloc: Allocated zero-initialized memory from a per-cpu pool set.
+ *
+ * Allocate memory for an item within the pool, and zero-initialize its
+ * memory on all CPUs. See rseq_percpu_pool_set_malloc for details.
+ *
+ * This API is MT-safe.
+ */
 void __rseq_percpu *rseq_percpu_pool_set_zmalloc(struct rseq_percpu_pool_set *pool_set, size_t len);
 
 #ifdef __cplusplus
diff --git a/src/rseq-percpu-alloc.c b/src/rseq-percpu-alloc.c
index 1c6cfc7..7d6498f 100644
--- a/src/rseq-percpu-alloc.c
+++ b/src/rseq-percpu-alloc.c
@@ -26,8 +26,8 @@
  *
  * The rseq per-CPU memory allocator allows the application the request
  * memory pools of CPU-Local memory each of containing objects of a
- * given size (rounded to next power of 2), a given virtual address size
- * per CPU, for a given maximum number of CPUs.
+ * given size (rounded to next power of 2), reserving a given virtual
+ * address size per CPU, for a given maximum number of CPUs.
  *
  * The per-CPU memory allocator is analogous to TLS (Thread-Local
  * Storage) memory: TLS is Thread-Local Storage, whereas the per-CPU