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 <[email protected]>
---
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: [email protected],[email protected]
+ *
+ * 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: [email protected],[email protected]
+ */
+
+/* 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
On 2023/10/17 21:56, wuqiang.matt wrote:
> 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
>
I'm curious why not just extend the existing lockless freelist to
percpu lockless freelists? And the percpu freelist is more flexible
to use than this percpu ring-array? The latter has to be fixed size
when creation.
Thanks.
> Signed-off-by: wuqiang.matt <[email protected]>
> ---
> 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: [email protected],[email protected]
> + *
> + * 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: [email protected],[email protected]
> + */
> +
> +/* 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);
On 2023/10/18 10:18, Chengming Zhou wrote:
> On 2023/10/17 21:56, wuqiang.matt wrote:
>> 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
>>
> I'm curious why not just extend the existing lockless freelist to
> percpu lockless freelists? And the percpu freelist is more flexible
> to use than this percpu ring-array? The latter has to be fixed size
> when creation.
I did that in first 2 versions, and abandoned it from the 3rd version.
The core reason is there are data races in freelist node:
After pop() from freelist, the freelist_node zone of the object could
be still in busy spinning by other nodes, so even the owner of this
object couldn't know when the races would go. freelist_zone is defined
as a union in the use cases (kretprobe), which brings potential issues.
If the object owner touches freelist_node:refs and then tries to push
to freelist to reclaim the object, freelist_add might just quit if
atomic_fetch_add_release(REFS_ON_FREELIST, &node->refs) returns true.
Keeping freelist_node as private could be fine, which is imposing an
extra rule to the users. Current ring array likes something moving
"freelist_node" to the ring array, which minimizes memory footprints.
Flexibility is not a strong requirement since all the use cases have
objects pre-allocated.
> Thanks.
Thank you.
>
>> Signed-off-by: wuqiang.matt <[email protected]>
>> ---
>> 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: [email protected],[email protected]
>> + *
>> + * 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: [email protected],[email protected]
>> + */
>> +
>> +/* 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);