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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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#ifndef _LINUX_OBJPOOL_H#define _LINUX_OBJPOOL_H
#include <linux/types.h>#include <linux/refcount.h>#include <linux/atomic.h>#include <linux/cpumask.h>#include <linux/irqflags.h>#include <linux/smp.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_possible_cpus: cached value of num_possible_cpus() * @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_possible_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);
/* 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;
/* * data visibility of 'last' and 'head' could be out of * order since memory updating of 'last' and 'head' are * performed in push() and pop() independently * * before any retrieving attempts, pop() must guarantee * 'last' is behind 'head', that is to say, there must * be available objects in slot, which could be ensured * by condition 'last != head && last - head <= nr_objs' * that is equivalent to 'last - head - 1 < nr_objs' as * 'last' and 'head' are both unsigned int32 */ if (READ_ONCE(slot->last) - head - 1 >= pool->nr_objs) { head = READ_ONCE(slot->head); continue; }
/* 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;}
/** * objpool_pop() - allocate an object from objpool * @pool: object pool * * return value: object ptr or NULL if failed */static inline void *objpool_pop(struct objpool_head *pool){ void *obj = NULL; unsigned long flags; int start, cpu;
/* disable local irq to avoid preemption & interruption */ raw_local_irq_save(flags);
start = raw_smp_processor_id(); for_each_possible_cpu_wrap(cpu, start) { obj = __objpool_try_get_slot(pool, cpu); if (obj) break; } raw_local_irq_restore(flags);
return obj;}
/* 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;}
/** * 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) */static inline 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;}
/** * 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 */