1/* SPDX-License-Identifier: GPL-2.0 */
2
3#ifndef _LINUX_OBJPOOL_H
4#define _LINUX_OBJPOOL_H
5
6#include <linux/types.h>
7#include <linux/refcount.h>
8
9/*
10 * objpool: ring-array based lockless MPMC queue
11 *
12 * Copyright: wuqiang.matt@bytedance.com,mhiramat@kernel.org
13 *
14 * objpool is a scalable implementation of high performance queue for
15 * object allocation and reclamation, such as kretprobe instances.
16 *
17 * With leveraging percpu ring-array to mitigate hot spots of memory
18 * contention, it delivers near-linear scalability for high parallel
19 * scenarios. The objpool is best suited for the following cases:
20 * 1) Memory allocation or reclamation are prohibited or too expensive
21 * 2) Consumers are of different priorities, such as irqs and threads
22 *
23 * Limitations:
24 * 1) Maximum objects (capacity) is fixed after objpool creation
25 * 2) All pre-allocated objects are managed in percpu ring array,
26 *    which consumes more memory than linked lists
27 */
28
29/**
30 * struct objpool_slot - percpu ring array of objpool
31 * @head: head sequence of the local ring array (to retrieve at)
32 * @tail: tail sequence of the local ring array (to append at)
33 * @last: the last sequence number marked as ready for retrieve
34 * @mask: bits mask for modulo capacity to compute array indexes
35 * @entries: object entries on this slot
36 *
37 * Represents a cpu-local array-based ring buffer, its size is specialized
38 * during initialization of object pool. The percpu objpool node is to be
39 * allocated from local memory for NUMA system, and to be kept compact in
40 * continuous memory: CPU assigned number of objects are stored just after
41 * the body of objpool_node.
42 *
43 * Real size of the ring array is far too smaller than the value range of
44 * head and tail, typed as uint32_t: [0, 2^32), so only lower bits (mask)
45 * of head and tail are used as the actual position in the ring array. In
46 * general the ring array is acting like a small sliding window, which is
47 * always moving forward in the loop of [0, 2^32).
48 */
49struct objpool_slot {
50	uint32_t            head;
51	uint32_t            tail;
52	uint32_t            last;
53	uint32_t            mask;
54	void               *entries[];
55} __packed;
56
57struct objpool_head;
58
59/*
60 * caller-specified callback for object initial setup, it's only called
61 * once for each object (just after the memory allocation of the object)
62 */
63typedef int (*objpool_init_obj_cb)(void *obj, void *context);
64
65/* caller-specified cleanup callback for objpool destruction */
66typedef int (*objpool_fini_cb)(struct objpool_head *head, void *context);
67
68/**
69 * struct objpool_head - object pooling metadata
70 * @obj_size:   object size, aligned to sizeof(void *)
71 * @nr_objs:    total objs (to be pre-allocated with objpool)
72 * @nr_cpus:    local copy of nr_cpu_ids
73 * @capacity:   max objs can be managed by one objpool_slot
74 * @gfp:        gfp flags for kmalloc & vmalloc
75 * @ref:        refcount of objpool
76 * @flags:      flags for objpool management
77 * @cpu_slots:  pointer to the array of objpool_slot
78 * @release:    resource cleanup callback
79 * @context:    caller-provided context
80 */
81struct objpool_head {
82	int                     obj_size;
83	int                     nr_objs;
84	int                     nr_cpus;
85	int                     capacity;
86	gfp_t                   gfp;
87	refcount_t              ref;
88	unsigned long           flags;
89	struct objpool_slot   **cpu_slots;
90	objpool_fini_cb         release;
91	void                   *context;
92};
93
94#define OBJPOOL_NR_OBJECT_MAX	(1UL << 24) /* maximum numbers of total objects */
95#define OBJPOOL_OBJECT_SIZE_MAX	(1UL << 16) /* maximum size of an object */
96
97/**
98 * objpool_init() - initialize objpool and pre-allocated objects
99 * @pool:    the object pool to be initialized, declared by caller
100 * @nr_objs: total objects to be pre-allocated by this object pool
101 * @object_size: size of an object (should be > 0)
102 * @gfp:     flags for memory allocation (via kmalloc or vmalloc)
103 * @context: user context for object initialization callback
104 * @objinit: object initialization callback for extra setup
105 * @release: cleanup callback for extra cleanup task
106 *
107 * return value: 0 for success, otherwise error code
108 *
109 * All pre-allocated objects are to be zeroed after memory allocation.
110 * Caller could do extra initialization in objinit callback. objinit()
111 * will be called just after slot allocation and called only once for
112 * each object. After that the objpool won't touch any content of the
113 * objects. It's caller's duty to perform reinitialization after each
114 * pop (object allocation) or do clearance before each push (object
115 * reclamation).
116 */
117int objpool_init(struct objpool_head *pool, int nr_objs, int object_size,
118		 gfp_t gfp, void *context, objpool_init_obj_cb objinit,
119		 objpool_fini_cb release);
120
121/**
122 * objpool_pop() - allocate an object from objpool
123 * @pool: object pool
124 *
125 * return value: object ptr or NULL if failed
126 */
127void *objpool_pop(struct objpool_head *pool);
128
129/**
130 * objpool_push() - reclaim the object and return back to objpool
131 * @obj:  object ptr to be pushed to objpool
132 * @pool: object pool
133 *
134 * return: 0 or error code (it fails only when user tries to push
135 * the same object multiple times or wrong "objects" into objpool)
136 */
137int objpool_push(void *obj, struct objpool_head *pool);
138
139/**
140 * objpool_drop() - discard the object and deref objpool
141 * @obj:  object ptr to be discarded
142 * @pool: object pool
143 *
144 * return: 0 if objpool was released; -EAGAIN if there are still
145 *         outstanding objects
146 *
147 * objpool_drop is normally for the release of outstanding objects
148 * after objpool cleanup (objpool_fini). Thinking of this example:
149 * kretprobe is unregistered and objpool_fini() is called to release
150 * all remained objects, but there are still objects being used by
151 * unfinished kretprobes (like blockable function: sys_accept). So
152 * only when the last outstanding object is dropped could the whole
153 * objpool be released along with the call of objpool_drop()
154 */
155int objpool_drop(void *obj, struct objpool_head *pool);
156
157/**
158 * objpool_free() - release objpool forcely (all objects to be freed)
159 * @pool: object pool to be released
160 */
161void objpool_free(struct objpool_head *pool);
162
163/**
164 * objpool_fini() - deref object pool (also releasing unused objects)
165 * @pool: object pool to be dereferenced
166 *
167 * objpool_fini() will try to release all remained free objects and
168 * then drop an extra reference of the objpool. If all objects are
169 * already returned to objpool (so called synchronous use cases),
170 * the objpool itself will be freed together. But if there are still
171 * outstanding objects (so called asynchronous use cases, such like
172 * blockable kretprobe), the objpool won't be released until all
173 * the outstanding objects are dropped, but the caller must assure
174 * there are no concurrent objpool_push() on the fly. Normally RCU
175 * is being required to make sure all ongoing objpool_push() must
176 * be finished before calling objpool_fini(), so does test_objpool,
177 * kretprobe or rethook
178 */
179void objpool_fini(struct objpool_head *pool);
180
181#endif /* _LINUX_OBJPOOL_H */
182