lib: objpool added: ring-array based lockless MPMC

/* 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.matt@bytedance.com,mhiramat@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 */

	 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

// 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.matt@bytedance.com,mhiramat@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);