objpool is a scalable implementation of high performance queue for
object allocation and reclamation, such as kretprobe instances.
With leveraging percpu ring-array to mitigate hot spots of memory
contention, it delivers near-linear scalability for high parallel
scenarios. The objpool is best suited for the following cases:
1) Memory allocation or reclamation are prohibited or too expensive
2) Consumers are of different priorities, such as irqs and threads
Limitations:
1) Maximum objects (capacity) is fixed after objpool creation
2) All pre-allocated objects are managed in percpu ring array,
which consumes more memory than linked lists
Signed-off-by: wuqiang.matt <wuqiang.m...@bytedance.com>
---
include/linux/objpool.h | 176 +++++++++++++++++++++++++
lib/Makefile | 2 +-
lib/objpool.c | 286 ++++++++++++++++++++++++++++++++++++++++
3 files changed, 463 insertions(+), 1 deletion(-)
create mode 100644 include/linux/objpool.h
create mode 100644 lib/objpool.c
diff --git a/include/linux/objpool.h b/include/linux/objpool.h
new file mode 100644
index 000000000000..4df18405420a
--- /dev/null
+++ b/include/linux/objpool.h
@@ -0,0 +1,181 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _LINUX_OBJPOOL_H
+#define _LINUX_OBJPOOL_H
+
+#include <linux/types.h>
+#include <linux/refcount.h>
+
+/*
+ * objpool: ring-array based lockless MPMC queue
+ *
+ * Copyright: wuqiang.m...@bytedance.com,mhira...@kernel.org
+ *
+ * objpool is a scalable implementation of high performance queue for
+ * object allocation and reclamation, such as kretprobe instances.
+ *
+ * With leveraging percpu ring-array to mitigate hot spots of memory
+ * contention, it delivers near-linear scalability for high parallel
+ * scenarios. The objpool is best suited for the following cases:
+ * 1) Memory allocation or reclamation are prohibited or too expensive
+ * 2) Consumers are of different priorities, such as irqs and threads
+ *
+ * Limitations:
+ * 1) Maximum objects (capacity) is fixed after objpool creation
+ * 2) All pre-allocated objects are managed in percpu ring array,
+ * which consumes more memory than linked lists
+ */
+
+/**
+ * struct objpool_slot - percpu ring array of objpool
+ * @head: head sequence of the local ring array (to retrieve at)
+ * @tail: tail sequence of the local ring array (to append at)
+ * @last: the last sequence number marked as ready for retrieve
+ * @mask: bits mask for modulo capacity to compute array indexes
+ * @entries: object entries on this slot
+ *
+ * Represents a cpu-local array-based ring buffer, its size is specialized
+ * during initialization of object pool. The percpu objpool node is to be
+ * allocated from local memory for NUMA system, and to be kept compact in
+ * continuous memory: CPU assigned number of objects are stored just after
+ * the body of objpool_node.
+ *
+ * Real size of the ring array is far too smaller than the value range of
+ * head and tail, typed as uint32_t: [0, 2^32), so only lower bits (mask)
+ * of head and tail are used as the actual position in the ring array. In
+ * general the ring array is acting like a small sliding window, which is
+ * always moving forward in the loop of [0, 2^32).
+ */
+struct objpool_slot {
+ uint32_t head;
+ uint32_t tail;
+ uint32_t last;
+ uint32_t mask;
+ void *entries[];
+} __packed;
+
+struct objpool_head;
+
+/*
+ * caller-specified callback for object initial setup, it's only called
+ * once for each object (just after the memory allocation of the object)
+ */
+typedef int (*objpool_init_obj_cb)(void *obj, void *context);
+
+/* caller-specified cleanup callback for objpool destruction */
+typedef int (*objpool_fini_cb)(struct objpool_head *head, void *context);
+
+/**
+ * struct objpool_head - object pooling metadata
+ * @obj_size: object size, aligned to sizeof(void *)
+ * @nr_objs: total objs (to be pre-allocated with objpool)
+ * @nr_cpus: local copy of nr_cpu_ids
+ * @capacity: max objs can be managed by one objpool_slot
+ * @gfp: gfp flags for kmalloc & vmalloc
+ * @ref: refcount of objpool
+ * @flags: flags for objpool management
+ * @cpu_slots: pointer to the array of objpool_slot
+ * @release: resource cleanup callback
+ * @context: caller-provided context
+ */
+struct objpool_head {
+ int obj_size;
+ int nr_objs;
+ int nr_cpus;
+ int capacity;
+ gfp_t gfp;
+ refcount_t ref;
+ unsigned long flags;
+ struct objpool_slot **cpu_slots;
+ objpool_fini_cb release;
+ void *context;
+};
+
+#define OBJPOOL_NR_OBJECT_MAX (1UL << 24) /* maximum numbers of total objects
*/
+#define OBJPOOL_OBJECT_SIZE_MAX (1UL << 16) /* maximum size of an
object */
+
+/**
+ * objpool_init() - initialize objpool and pre-allocated objects
+ * @pool: the object pool to be initialized, declared by caller
+ * @nr_objs: total objects to be pre-allocated by this object pool
+ * @object_size: size of an object (should be > 0)
+ * @gfp: flags for memory allocation (via kmalloc or vmalloc)
+ * @context: user context for object initialization callback
+ * @objinit: object initialization callback for extra setup
+ * @release: cleanup callback for extra cleanup task
+ *
+ * return value: 0 for success, otherwise error code
+ *
+ * All pre-allocated objects are to be zeroed after memory allocation.
+ * Caller could do extra initialization in objinit callback. objinit()
+ * will be called just after slot allocation and called only once for
+ * each object. After that the objpool won't touch any content of the
+ * objects. It's caller's duty to perform reinitialization after each
+ * pop (object allocation) or do clearance before each push (object
+ * reclamation).
+ */
+int objpool_init(struct objpool_head *pool, int nr_objs, int object_size,
+ gfp_t gfp, void *context, objpool_init_obj_cb objinit,
+ objpool_fini_cb release);
+
+/**
+ * objpool_pop() - allocate an object from objpool
+ * @pool: object pool
+ *
+ * return value: object ptr or NULL if failed
+ */
+void *objpool_pop(struct objpool_head *pool);
+
+/**
+ * objpool_push() - reclaim the object and return back to objpool
+ * @obj: object ptr to be pushed to objpool
+ * @pool: object pool
+ *
+ * return: 0 or error code (it fails only when user tries to push
+ * the same object multiple times or wrong "objects" into objpool)
+ */
+int objpool_push(void *obj, struct objpool_head *pool);
+
+/**
+ * objpool_drop() - discard the object and deref objpool
+ * @obj: object ptr to be discarded
+ * @pool: object pool
+ *
+ * return: 0 if objpool was released; -EAGAIN if there are still
+ * outstanding objects
+ *
+ * objpool_drop is normally for the release of outstanding objects
+ * after objpool cleanup (objpool_fini). Thinking of this example:
+ * kretprobe is unregistered and objpool_fini() is called to release
+ * all remained objects, but there are still objects being used by
+ * unfinished kretprobes (like blockable function: sys_accept). So
+ * only when the last outstanding object is dropped could the whole
+ * objpool be released along with the call of objpool_drop()
+ */
+int objpool_drop(void *obj, struct objpool_head *pool);
+
+/**
+ * objpool_free() - release objpool forcely (all objects to be freed)
+ * @pool: object pool to be released
+ */
+void objpool_free(struct objpool_head *pool);
+
+/**
+ * objpool_fini() - deref object pool (also releasing unused objects)
+ * @pool: object pool to be dereferenced
+ *
+ * objpool_fini() will try to release all remained free objects and
+ * then drop an extra reference of the objpool. If all objects are
+ * already returned to objpool (so called synchronous use cases),
+ * the objpool itself will be freed together. But if there are still
+ * outstanding objects (so called asynchronous use cases, such like
+ * blockable kretprobe), the objpool won't be released until all
+ * the outstanding objects are dropped, but the caller must assure
+ * there are no concurrent objpool_push() on the fly. Normally RCU
+ * is being required to make sure all ongoing objpool_push() must
+ * be finished before calling objpool_fini(), so does test_objpool,
+ * kretprobe or rethook
+ */
+void objpool_fini(struct objpool_head *pool);
+
+#endif /* _LINUX_OBJPOOL_H */
diff --git a/lib/Makefile b/lib/Makefile
index 1ffae65bb7ee..7a84c922d9ff 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -34,7 +34,7 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \
is_single_threaded.o plist.o decompress.o kobject_uevent.o \
earlycpio.o seq_buf.o siphash.o dec_and_lock.o \
nmi_backtrace.o win_minmax.o memcat_p.o \
- buildid.o
+ buildid.o objpool.o
lib-$(CONFIG_PRINTK) += dump_stack.o
lib-$(CONFIG_SMP) += cpumask.o
diff --git a/lib/objpool.c b/lib/objpool.c
new file mode 100644
index 000000000000..37a71e063f18
--- /dev/null
+++ b/lib/objpool.c
@@ -0,0 +1,280 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/objpool.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+#include <linux/atomic.h>
+#include <linux/irqflags.h>
+#include <linux/cpumask.h>
+#include <linux/log2.h>
+
+/*
+ * objpool: ring-array based lockless MPMC/FIFO queues
+ *
+ * Copyright: wuqiang.m...@bytedance.com,mhira...@kernel.org
+ */
+
+/* initialize percpu objpool_slot */
+static int
+objpool_init_percpu_slot(struct objpool_head *pool,
+ struct objpool_slot *slot,
+ int nodes, void *context,
+ objpool_init_obj_cb objinit)
+{
+ void *obj = (void *)&slot->entries[pool->capacity];
+ int i;
+
+ /* initialize elements of percpu objpool_slot */
+ slot->mask = pool->capacity - 1;
+
+ for (i = 0; i < nodes; i++) {
+ if (objinit) {
+ int rc = objinit(obj, context);
+ if (rc)
+ return rc;
+ }
+ slot->entries[slot->tail & slot->mask] = obj;
+ obj = obj + pool->obj_size;
+ slot->tail++;
+ slot->last = slot->tail;
+ pool->nr_objs++;
+ }
+
+ return 0;
+}
+
+/* allocate and initialize percpu slots */
+static int
+objpool_init_percpu_slots(struct objpool_head *pool, int nr_objs,
+ void *context, objpool_init_obj_cb objinit)
+{
+ int i, cpu_count = 0;
+
+ for (i = 0; i < pool->nr_cpus; i++) {
+
+ struct objpool_slot *slot;
+ int nodes, size, rc;
+
+ /* skip the cpu node which could never be present */
+ if (!cpu_possible(i))
+ continue;
+
+ /* compute how many objects to be allocated with this slot */
+ nodes = nr_objs / num_possible_cpus();
+ if (cpu_count < (nr_objs % num_possible_cpus()))
+ nodes++;
+ cpu_count++;
+
+ size = struct_size(slot, entries, pool->capacity) +
+ pool->obj_size * nodes;
+
+ /*
+ * here we allocate percpu-slot & objs together in a single
+ * allocation to make it more compact, taking advantage of
+ * warm caches and TLB hits. in default vmalloc is used to
+ * reduce the pressure of kernel slab system. as we know,
+ * mimimal size of vmalloc is one page since vmalloc would
+ * always align the requested size to page size
+ */
+ if (pool->gfp & GFP_ATOMIC)
+ slot = kmalloc_node(size, pool->gfp, cpu_to_node(i));
+ else
+ slot = __vmalloc_node(size, sizeof(void *), pool->gfp,
+ cpu_to_node(i), __builtin_return_address(0));
+ if (!slot)
+ return -ENOMEM;
+ memset(slot, 0, size);
+ pool->cpu_slots[i] = slot;
+
+ /* initialize the objpool_slot of cpu node i */
+ rc = objpool_init_percpu_slot(pool, slot, nodes, context,
objinit);
+ if (rc)
+ return rc;
+ }
+
+ return 0;
+}
+
+/* cleanup all percpu slots of the object pool */
+static void objpool_fini_percpu_slots(struct objpool_head *pool)
+{
+ int i;
+
+ if (!pool->cpu_slots)
+ return;
+
+ for (i = 0; i < pool->nr_cpus; i++)
+ kvfree(pool->cpu_slots[i]);
+ kfree(pool->cpu_slots);
+}
+
+/* initialize object pool and pre-allocate objects */
+int objpool_init(struct objpool_head *pool, int nr_objs, int object_size,
+ gfp_t gfp, void *context, objpool_init_obj_cb objinit,
+ objpool_fini_cb release)
+{
+ int rc, capacity, slot_size;
+
+ /* check input parameters */
+ if (nr_objs <= 0 || nr_objs > OBJPOOL_NR_OBJECT_MAX ||
+ object_size <= 0 || object_size > OBJPOOL_OBJECT_SIZE_MAX)
+ return -EINVAL;
+
+ /* align up to unsigned long size */
+ object_size = ALIGN(object_size, sizeof(long));
+
+ /* calculate capacity of percpu objpool_slot */
+ capacity = roundup_pow_of_two(nr_objs);
+ if (!capacity)
+ return -EINVAL;
+
+ /* initialize objpool pool */
+ memset(pool, 0, sizeof(struct objpool_head));
+ pool->nr_cpus = nr_cpu_ids;
+ pool->obj_size = object_size;
+ pool->capacity = capacity;
+ pool->gfp = gfp & ~__GFP_ZERO;
+ pool->context = context;
+ pool->release = release;
+ slot_size = pool->nr_cpus * sizeof(struct objpool_slot);
+ pool->cpu_slots = kzalloc(slot_size, pool->gfp);
+ if (!pool->cpu_slots)
+ return -ENOMEM;
+
+ /* initialize per-cpu slots */
+ rc = objpool_init_percpu_slots(pool, nr_objs, context, objinit);
+ if (rc)
+ objpool_fini_percpu_slots(pool);
+ else
+ refcount_set(&pool->ref, pool->nr_objs + 1);
+
+ return rc;
+}
+EXPORT_SYMBOL_GPL(objpool_init);
+
+/* adding object to slot, abort if the slot was already full */
+static inline int
+objpool_try_add_slot(void *obj, struct objpool_head *pool, int cpu)
+{
+ struct objpool_slot *slot = pool->cpu_slots[cpu];
+ uint32_t head, tail;
+
+ /* loading tail and head as a local snapshot, tail first */
+ tail = READ_ONCE(slot->tail);
+
+ do {
+ head = READ_ONCE(slot->head);
+ /* fault caught: something must be wrong */
+ WARN_ON_ONCE(tail - head > pool->nr_objs);
+ } while (!try_cmpxchg_acquire(&slot->tail, &tail, tail + 1));
+
+ /* now the tail position is reserved for the given obj */
+ WRITE_ONCE(slot->entries[tail & slot->mask], obj);
+ /* update sequence to make this obj available for pop() */
+ smp_store_release(&slot->last, tail + 1);
+
+ return 0;
+}
+
+/* reclaim an object to object pool */
+int objpool_push(void *obj, struct objpool_head *pool)
+{
+ unsigned long flags;
+ int rc;
+
+ /* disable local irq to avoid preemption & interruption */
+ raw_local_irq_save(flags);
+ rc = objpool_try_add_slot(obj, pool, raw_smp_processor_id());
+ raw_local_irq_restore(flags);
+
+ return rc;
+}
+EXPORT_SYMBOL_GPL(objpool_push);
+
+/* try to retrieve object from slot */
+static inline void *objpool_try_get_slot(struct objpool_head *pool, int cpu)
+{
+ struct objpool_slot *slot = pool->cpu_slots[cpu];
+ /* load head snapshot, other cpus may change it */
+ uint32_t head = smp_load_acquire(&slot->head);
+
+ while (head != READ_ONCE(slot->last)) {
+ void *obj;
+
+ /* obj must be retrieved before moving forward head */
+ obj = READ_ONCE(slot->entries[head & slot->mask]);
+
+ /* move head forward to mark it's consumption */
+ if (try_cmpxchg_release(&slot->head, &head, head + 1))
+ return obj;
+ }
+
+ return NULL;
+}
+
+/* allocate an object from object pool */
+void *objpool_pop(struct objpool_head *pool)
+{
+ void *obj = NULL;
+ unsigned long flags;
+ int i, cpu;
+
+ /* disable local irq to avoid preemption & interruption */
+ raw_local_irq_save(flags);
+
+ cpu = raw_smp_processor_id();
+ for (i = 0; i < num_possible_cpus(); i++) {
+ obj = objpool_try_get_slot(pool, cpu);
+ if (obj)
+ break;
+ cpu = cpumask_next_wrap(cpu, cpu_possible_mask, -1, 1);
+ }
+ raw_local_irq_restore(flags);
+
+ return obj;
+}
+EXPORT_SYMBOL_GPL(objpool_pop);
+
+/* release whole objpool forcely */
+void objpool_free(struct objpool_head *pool)
+{
+ if (!pool->cpu_slots)
+ return;
+
+ /* release percpu slots */
+ objpool_fini_percpu_slots(pool);
+
+ /* call user's cleanup callback if provided */
+ if (pool->release)
+ pool->release(pool, pool->context);
+}
+EXPORT_SYMBOL_GPL(objpool_free);
+
+/* drop the allocated object, rather reclaim it to objpool */
+int objpool_drop(void *obj, struct objpool_head *pool)
+{
+ if (!obj || !pool)
+ return -EINVAL;
+
+ if (refcount_dec_and_test(&pool->ref)) {
+ objpool_free(pool);
+ return 0;
+ }
+
+ return -EAGAIN;
+}
+EXPORT_SYMBOL_GPL(objpool_drop);
+
+/* drop unused objects and defref objpool for releasing */
+void objpool_fini(struct objpool_head *pool)
+{
+ int count = 1; /* extra ref for objpool itself */
+
+ /* drop all remained objects from objpool */
+ while (objpool_pop(pool))
+ count++;
+
+ if (refcount_sub_and_test(count, &pool->ref))
+ objpool_free(pool);
+}
+EXPORT_SYMBOL_GPL(objpool_fini);
--
2.40.1
