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#include <linux/atomic.h>
9#include <linux/cpumask.h>
10#include <linux/irqflags.h>
11#include <linux/smp.h>
12
13/*
14 * objpool: ring-array based lockless MPMC queue
15 *
16 * Copyright: wuqiang.matt@bytedance.com,mhiramat@kernel.org
17 *
18 * objpool is a scalable implementation of high performance queue for
19 * object allocation and reclamation, such as kretprobe instances.
20 *
21 * With leveraging percpu ring-array to mitigate hot spots of memory
22 * contention, it delivers near-linear scalability for high parallel
23 * scenarios. The objpool is best suited for the following cases:
24 * 1) Memory allocation or reclamation are prohibited or too expensive
25 * 2) Consumers are of different priorities, such as irqs and threads
26 *
27 * Limitations:
28 * 1) Maximum objects (capacity) is fixed after objpool creation
29 * 2) All pre-allocated objects are managed in percpu ring array,
30 * which consumes more memory than linked lists
31 */
32
33/**
34 * struct objpool_slot - percpu ring array of objpool
35 * @head: head sequence of the local ring array (to retrieve at)
36 * @tail: tail sequence of the local ring array (to append at)
37 * @last: the last sequence number marked as ready for retrieve
38 * @mask: bits mask for modulo capacity to compute array indexes
39 * @entries: object entries on this slot
40 *
41 * Represents a cpu-local array-based ring buffer, its size is specialized
42 * during initialization of object pool. The percpu objpool node is to be
43 * allocated from local memory for NUMA system, and to be kept compact in
44 * continuous memory: CPU assigned number of objects are stored just after
45 * the body of objpool_node.
46 *
47 * Real size of the ring array is far too smaller than the value range of
48 * head and tail, typed as uint32_t: [0, 2^32), so only lower bits (mask)
49 * of head and tail are used as the actual position in the ring array. In
50 * general the ring array is acting like a small sliding window, which is
51 * always moving forward in the loop of [0, 2^32).
52 */
53struct objpool_slot {
54 uint32_t head;
55 uint32_t tail;
56 uint32_t last;
57 uint32_t mask;
58 void *entries[];
59} __packed;
60
61struct objpool_head;
62
63/*
64 * caller-specified callback for object initial setup, it's only called
65 * once for each object (just after the memory allocation of the object)
66 */
67typedef int (*objpool_init_obj_cb)(void *obj, void *context);
68
69/* caller-specified cleanup callback for objpool destruction */
70typedef int (*objpool_fini_cb)(struct objpool_head *head, void *context);
71
72/**
73 * struct objpool_head - object pooling metadata
74 * @obj_size: object size, aligned to sizeof(void *)
75 * @nr_objs: total objs (to be pre-allocated with objpool)
76 * @nr_possible_cpus: cached value of num_possible_cpus()
77 * @capacity: max objs can be managed by one objpool_slot
78 * @gfp: gfp flags for kmalloc & vmalloc
79 * @ref: refcount of objpool
80 * @flags: flags for objpool management
81 * @cpu_slots: pointer to the array of objpool_slot
82 * @release: resource cleanup callback
83 * @context: caller-provided context
84 */
85struct objpool_head {
86 int obj_size;
87 int nr_objs;
88 int nr_possible_cpus;
89 int capacity;
90 gfp_t gfp;
91 refcount_t ref;
92 unsigned long flags;
93 struct objpool_slot **cpu_slots;
94 objpool_fini_cb release;
95 void *context;
96};
97
98#define OBJPOOL_NR_OBJECT_MAX (1UL << 24) /* maximum numbers of total objects */
99#define OBJPOOL_OBJECT_SIZE_MAX (1UL << 16) /* maximum size of an object */
100
101/**
102 * objpool_init() - initialize objpool and pre-allocated objects
103 * @pool: the object pool to be initialized, declared by caller
104 * @nr_objs: total objects to be pre-allocated by this object pool
105 * @object_size: size of an object (should be > 0)
106 * @gfp: flags for memory allocation (via kmalloc or vmalloc)
107 * @context: user context for object initialization callback
108 * @objinit: object initialization callback for extra setup
109 * @release: cleanup callback for extra cleanup task
110 *
111 * return value: 0 for success, otherwise error code
112 *
113 * All pre-allocated objects are to be zeroed after memory allocation.
114 * Caller could do extra initialization in objinit callback. objinit()
115 * will be called just after slot allocation and called only once for
116 * each object. After that the objpool won't touch any content of the
117 * objects. It's caller's duty to perform reinitialization after each
118 * pop (object allocation) or do clearance before each push (object
119 * reclamation).
120 */
121int objpool_init(struct objpool_head *pool, int nr_objs, int object_size,
122 gfp_t gfp, void *context, objpool_init_obj_cb objinit,
123 objpool_fini_cb release);
124
125/* try to retrieve object from slot */
126static inline void *__objpool_try_get_slot(struct objpool_head *pool, int cpu)
127{
128 struct objpool_slot *slot = pool->cpu_slots[cpu];
129 /* load head snapshot, other cpus may change it */
130 uint32_t head = smp_load_acquire(&slot->head);
131
132 while (head != READ_ONCE(slot->last)) {
133 void *obj;
134
135 /*
136 * data visibility of 'last' and 'head' could be out of
137 * order since memory updating of 'last' and 'head' are
138 * performed in push() and pop() independently
139 *
140 * before any retrieving attempts, pop() must guarantee
141 * 'last' is behind 'head', that is to say, there must
142 * be available objects in slot, which could be ensured
143 * by condition 'last != head && last - head <= nr_objs'
144 * that is equivalent to 'last - head - 1 < nr_objs' as
145 * 'last' and 'head' are both unsigned int32
146 */
147 if (READ_ONCE(slot->last) - head - 1 >= pool->nr_objs) {
148 head = READ_ONCE(slot->head);
149 continue;
150 }
151
152 /* obj must be retrieved before moving forward head */
153 obj = READ_ONCE(slot->entries[head & slot->mask]);
154
155 /* move head forward to mark it's consumption */
156 if (try_cmpxchg_release(&slot->head, &head, head + 1))
157 return obj;
158 }
159
160 return NULL;
161}
162
163/**
164 * objpool_pop() - allocate an object from objpool
165 * @pool: object pool
166 *
167 * return value: object ptr or NULL if failed
168 */
169static inline void *objpool_pop(struct objpool_head *pool)
170{
171 void *obj = NULL;
172 unsigned long flags;
173 int start, cpu;
174
175 /* disable local irq to avoid preemption & interruption */
176 raw_local_irq_save(flags);
177
178 start = raw_smp_processor_id();
179 for_each_possible_cpu_wrap(cpu, start) {
180 obj = __objpool_try_get_slot(pool, cpu);
181 if (obj)
182 break;
183 }
184 raw_local_irq_restore(flags);
185
186 return obj;
187}
188
189/* adding object to slot, abort if the slot was already full */
190static inline int
191__objpool_try_add_slot(void *obj, struct objpool_head *pool, int cpu)
192{
193 struct objpool_slot *slot = pool->cpu_slots[cpu];
194 uint32_t head, tail;
195
196 /* loading tail and head as a local snapshot, tail first */
197 tail = READ_ONCE(slot->tail);
198
199 do {
200 head = READ_ONCE(slot->head);
201 /* fault caught: something must be wrong */
202 WARN_ON_ONCE(tail - head > pool->nr_objs);
203 } while (!try_cmpxchg_acquire(&slot->tail, &tail, tail + 1));
204
205 /* now the tail position is reserved for the given obj */
206 WRITE_ONCE(slot->entries[tail & slot->mask], obj);
207 /* update sequence to make this obj available for pop() */
208 smp_store_release(&slot->last, tail + 1);
209
210 return 0;
211}
212
213/**
214 * objpool_push() - reclaim the object and return back to objpool
215 * @obj: object ptr to be pushed to objpool
216 * @pool: object pool
217 *
218 * return: 0 or error code (it fails only when user tries to push
219 * the same object multiple times or wrong "objects" into objpool)
220 */
221static inline int objpool_push(void *obj, struct objpool_head *pool)
222{
223 unsigned long flags;
224 int rc;
225
226 /* disable local irq to avoid preemption & interruption */
227 raw_local_irq_save(flags);
228 rc = __objpool_try_add_slot(obj, pool, raw_smp_processor_id());
229 raw_local_irq_restore(flags);
230
231 return rc;
232}
233
234
235/**
236 * objpool_drop() - discard the object and deref objpool
237 * @obj: object ptr to be discarded
238 * @pool: object pool
239 *
240 * return: 0 if objpool was released; -EAGAIN if there are still
241 * outstanding objects
242 *
243 * objpool_drop is normally for the release of outstanding objects
244 * after objpool cleanup (objpool_fini). Thinking of this example:
245 * kretprobe is unregistered and objpool_fini() is called to release
246 * all remained objects, but there are still objects being used by
247 * unfinished kretprobes (like blockable function: sys_accept). So
248 * only when the last outstanding object is dropped could the whole
249 * objpool be released along with the call of objpool_drop()
250 */
251int objpool_drop(void *obj, struct objpool_head *pool);
252
253/**
254 * objpool_free() - release objpool forcely (all objects to be freed)
255 * @pool: object pool to be released
256 */
257void objpool_free(struct objpool_head *pool);
258
259/**
260 * objpool_fini() - deref object pool (also releasing unused objects)
261 * @pool: object pool to be dereferenced
262 *
263 * objpool_fini() will try to release all remained free objects and
264 * then drop an extra reference of the objpool. If all objects are
265 * already returned to objpool (so called synchronous use cases),
266 * the objpool itself will be freed together. But if there are still
267 * outstanding objects (so called asynchronous use cases, such like
268 * blockable kretprobe), the objpool won't be released until all
269 * the outstanding objects are dropped, but the caller must assure
270 * there are no concurrent objpool_push() on the fly. Normally RCU
271 * is being required to make sure all ongoing objpool_push() must
272 * be finished before calling objpool_fini(), so does test_objpool,
273 * kretprobe or rethook
274 */
275void objpool_fini(struct objpool_head *pool);
276
277#endif /* _LINUX_OBJPOOL_H */
278

source code of linux/include/linux/objpool.h

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