summaryrefslogtreecommitdiff
path: root/include/linux/objpool.h
blob: 15aff4a17f0cb0e55ee440ab9c4c701b49a5abb4 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
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: 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 */