182 lines
6.9 KiB
C
182 lines
6.9 KiB
C
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/* SPDX-License-Identifier: GPL-2.0 */
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#ifndef _LINUX_OBJPOOL_H
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#define _LINUX_OBJPOOL_H
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#include <linux/types.h>
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#include <linux/refcount.h>
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/*
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* objpool: ring-array based lockless MPMC queue
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*
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* Copyright: wuqiang.matt@bytedance.com,mhiramat@kernel.org
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*
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* objpool is a scalable implementation of high performance queue for
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* object allocation and reclamation, such as kretprobe instances.
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*
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* With leveraging percpu ring-array to mitigate hot spots of memory
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* contention, it delivers near-linear scalability for high parallel
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* scenarios. The objpool is best suited for the following cases:
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* 1) Memory allocation or reclamation are prohibited or too expensive
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* 2) Consumers are of different priorities, such as irqs and threads
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*
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* Limitations:
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* 1) Maximum objects (capacity) is fixed after objpool creation
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* 2) All pre-allocated objects are managed in percpu ring array,
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* which consumes more memory than linked lists
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*/
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/**
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* struct objpool_slot - percpu ring array of objpool
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* @head: head sequence of the local ring array (to retrieve at)
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* @tail: tail sequence of the local ring array (to append at)
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* @last: the last sequence number marked as ready for retrieve
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* @mask: bits mask for modulo capacity to compute array indexes
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* @entries: object entries on this slot
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*
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* Represents a cpu-local array-based ring buffer, its size is specialized
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* during initialization of object pool. The percpu objpool node is to be
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* allocated from local memory for NUMA system, and to be kept compact in
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* continuous memory: CPU assigned number of objects are stored just after
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* the body of objpool_node.
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*
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* Real size of the ring array is far too smaller than the value range of
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* head and tail, typed as uint32_t: [0, 2^32), so only lower bits (mask)
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* of head and tail are used as the actual position in the ring array. In
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* general the ring array is acting like a small sliding window, which is
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* always moving forward in the loop of [0, 2^32).
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*/
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struct objpool_slot {
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uint32_t head;
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uint32_t tail;
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uint32_t last;
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uint32_t mask;
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void *entries[];
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} __packed;
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struct objpool_head;
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/*
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* caller-specified callback for object initial setup, it's only called
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* once for each object (just after the memory allocation of the object)
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*/
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typedef int (*objpool_init_obj_cb)(void *obj, void *context);
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/* caller-specified cleanup callback for objpool destruction */
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typedef int (*objpool_fini_cb)(struct objpool_head *head, void *context);
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/**
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* struct objpool_head - object pooling metadata
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* @obj_size: object size, aligned to sizeof(void *)
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* @nr_objs: total objs (to be pre-allocated with objpool)
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* @nr_cpus: local copy of nr_cpu_ids
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* @capacity: max objs can be managed by one objpool_slot
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* @gfp: gfp flags for kmalloc & vmalloc
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* @ref: refcount of objpool
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* @flags: flags for objpool management
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* @cpu_slots: pointer to the array of objpool_slot
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* @release: resource cleanup callback
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* @context: caller-provided context
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*/
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struct objpool_head {
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int obj_size;
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int nr_objs;
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int nr_cpus;
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int capacity;
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gfp_t gfp;
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refcount_t ref;
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unsigned long flags;
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struct objpool_slot **cpu_slots;
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objpool_fini_cb release;
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void *context;
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};
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#define OBJPOOL_NR_OBJECT_MAX (1UL << 24) /* maximum numbers of total objects */
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#define OBJPOOL_OBJECT_SIZE_MAX (1UL << 16) /* maximum size of an object */
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/**
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* objpool_init() - initialize objpool and pre-allocated objects
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* @pool: the object pool to be initialized, declared by caller
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* @nr_objs: total objects to be pre-allocated by this object pool
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* @object_size: size of an object (should be > 0)
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* @gfp: flags for memory allocation (via kmalloc or vmalloc)
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* @context: user context for object initialization callback
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* @objinit: object initialization callback for extra setup
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* @release: cleanup callback for extra cleanup task
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*
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* return value: 0 for success, otherwise error code
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*
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* All pre-allocated objects are to be zeroed after memory allocation.
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* Caller could do extra initialization in objinit callback. objinit()
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* will be called just after slot allocation and called only once for
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* each object. After that the objpool won't touch any content of the
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* objects. It's caller's duty to perform reinitialization after each
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* pop (object allocation) or do clearance before each push (object
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* reclamation).
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*/
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int objpool_init(struct objpool_head *pool, int nr_objs, int object_size,
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gfp_t gfp, void *context, objpool_init_obj_cb objinit,
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objpool_fini_cb release);
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/**
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* objpool_pop() - allocate an object from objpool
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* @pool: object pool
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*
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* return value: object ptr or NULL if failed
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*/
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void *objpool_pop(struct objpool_head *pool);
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/**
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* objpool_push() - reclaim the object and return back to objpool
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* @obj: object ptr to be pushed to objpool
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* @pool: object pool
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*
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* return: 0 or error code (it fails only when user tries to push
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* the same object multiple times or wrong "objects" into objpool)
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*/
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int objpool_push(void *obj, struct objpool_head *pool);
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/**
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* objpool_drop() - discard the object and deref objpool
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* @obj: object ptr to be discarded
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* @pool: object pool
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*
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* return: 0 if objpool was released; -EAGAIN if there are still
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* outstanding objects
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*
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* objpool_drop is normally for the release of outstanding objects
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* after objpool cleanup (objpool_fini). Thinking of this example:
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* kretprobe is unregistered and objpool_fini() is called to release
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* all remained objects, but there are still objects being used by
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* unfinished kretprobes (like blockable function: sys_accept). So
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* only when the last outstanding object is dropped could the whole
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* objpool be released along with the call of objpool_drop()
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*/
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int objpool_drop(void *obj, struct objpool_head *pool);
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/**
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* objpool_free() - release objpool forcely (all objects to be freed)
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* @pool: object pool to be released
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*/
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void objpool_free(struct objpool_head *pool);
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/**
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* objpool_fini() - deref object pool (also releasing unused objects)
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* @pool: object pool to be dereferenced
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*
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* objpool_fini() will try to release all remained free objects and
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* then drop an extra reference of the objpool. If all objects are
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* already returned to objpool (so called synchronous use cases),
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* the objpool itself will be freed together. But if there are still
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* outstanding objects (so called asynchronous use cases, such like
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* blockable kretprobe), the objpool won't be released until all
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* the outstanding objects are dropped, but the caller must assure
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* there are no concurrent objpool_push() on the fly. Normally RCU
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* is being required to make sure all ongoing objpool_push() must
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* be finished before calling objpool_fini(), so does test_objpool,
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* kretprobe or rethook
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*/
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void objpool_fini(struct objpool_head *pool);
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#endif /* _LINUX_OBJPOOL_H */
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