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Johannes Weiner3e32cb22014-12-10 15:42:31 -08001/*
2 * Lockless hierarchical page accounting & limiting
3 *
4 * Copyright (C) 2014 Red Hat, Inc., Johannes Weiner
5 */
6
7#include <linux/page_counter.h>
8#include <linux/atomic.h>
9#include <linux/kernel.h>
10#include <linux/string.h>
11#include <linux/sched.h>
12#include <linux/bug.h>
13#include <asm/page.h>
14
15/**
16 * page_counter_cancel - take pages out of the local counter
17 * @counter: counter
18 * @nr_pages: number of pages to cancel
Johannes Weiner3e32cb22014-12-10 15:42:31 -080019 */
Johannes Weiner64f21992014-12-10 15:42:45 -080020void page_counter_cancel(struct page_counter *counter, unsigned long nr_pages)
Johannes Weiner3e32cb22014-12-10 15:42:31 -080021{
22 long new;
23
24 new = atomic_long_sub_return(nr_pages, &counter->count);
Johannes Weiner3e32cb22014-12-10 15:42:31 -080025 /* More uncharges than charges? */
26 WARN_ON_ONCE(new < 0);
Johannes Weiner3e32cb22014-12-10 15:42:31 -080027}
28
29/**
30 * page_counter_charge - hierarchically charge pages
31 * @counter: counter
32 * @nr_pages: number of pages to charge
33 *
34 * NOTE: This does not consider any configured counter limits.
35 */
36void page_counter_charge(struct page_counter *counter, unsigned long nr_pages)
37{
38 struct page_counter *c;
39
40 for (c = counter; c; c = c->parent) {
41 long new;
42
43 new = atomic_long_add_return(nr_pages, &c->count);
44 /*
45 * This is indeed racy, but we can live with some
46 * inaccuracy in the watermark.
47 */
48 if (new > c->watermark)
49 c->watermark = new;
50 }
51}
52
53/**
54 * page_counter_try_charge - try to hierarchically charge pages
55 * @counter: counter
56 * @nr_pages: number of pages to charge
57 * @fail: points first counter to hit its limit, if any
58 *
Johannes Weiner6071ca52015-11-05 18:50:26 -080059 * Returns %true on success, or %false and @fail if the counter or one
60 * of its ancestors has hit its configured limit.
Johannes Weiner3e32cb22014-12-10 15:42:31 -080061 */
Johannes Weiner6071ca52015-11-05 18:50:26 -080062bool page_counter_try_charge(struct page_counter *counter,
63 unsigned long nr_pages,
64 struct page_counter **fail)
Johannes Weiner3e32cb22014-12-10 15:42:31 -080065{
66 struct page_counter *c;
67
68 for (c = counter; c; c = c->parent) {
69 long new;
70 /*
71 * Charge speculatively to avoid an expensive CAS. If
72 * a bigger charge fails, it might falsely lock out a
73 * racing smaller charge and send it into reclaim
74 * early, but the error is limited to the difference
75 * between the two sizes, which is less than 2M/4M in
76 * case of a THP locking out a regular page charge.
77 *
78 * The atomic_long_add_return() implies a full memory
79 * barrier between incrementing the count and reading
80 * the limit. When racing with page_counter_limit(),
81 * we either see the new limit or the setter sees the
82 * counter has changed and retries.
83 */
84 new = atomic_long_add_return(nr_pages, &c->count);
85 if (new > c->limit) {
86 atomic_long_sub(nr_pages, &c->count);
87 /*
88 * This is racy, but we can live with some
89 * inaccuracy in the failcnt.
90 */
91 c->failcnt++;
92 *fail = c;
93 goto failed;
94 }
95 /*
96 * Just like with failcnt, we can live with some
97 * inaccuracy in the watermark.
98 */
99 if (new > c->watermark)
100 c->watermark = new;
101 }
Johannes Weiner6071ca52015-11-05 18:50:26 -0800102 return true;
Johannes Weiner3e32cb22014-12-10 15:42:31 -0800103
104failed:
105 for (c = counter; c != *fail; c = c->parent)
106 page_counter_cancel(c, nr_pages);
107
Johannes Weiner6071ca52015-11-05 18:50:26 -0800108 return false;
Johannes Weiner3e32cb22014-12-10 15:42:31 -0800109}
110
111/**
112 * page_counter_uncharge - hierarchically uncharge pages
113 * @counter: counter
114 * @nr_pages: number of pages to uncharge
Johannes Weiner3e32cb22014-12-10 15:42:31 -0800115 */
Johannes Weiner64f21992014-12-10 15:42:45 -0800116void page_counter_uncharge(struct page_counter *counter, unsigned long nr_pages)
Johannes Weiner3e32cb22014-12-10 15:42:31 -0800117{
118 struct page_counter *c;
Johannes Weiner3e32cb22014-12-10 15:42:31 -0800119
Johannes Weiner64f21992014-12-10 15:42:45 -0800120 for (c = counter; c; c = c->parent)
121 page_counter_cancel(c, nr_pages);
Johannes Weiner3e32cb22014-12-10 15:42:31 -0800122}
123
124/**
125 * page_counter_limit - limit the number of pages allowed
126 * @counter: counter
127 * @limit: limit to set
128 *
129 * Returns 0 on success, -EBUSY if the current number of pages on the
130 * counter already exceeds the specified limit.
131 *
132 * The caller must serialize invocations on the same counter.
133 */
134int page_counter_limit(struct page_counter *counter, unsigned long limit)
135{
136 for (;;) {
137 unsigned long old;
138 long count;
139
140 /*
141 * Update the limit while making sure that it's not
142 * below the concurrently-changing counter value.
143 *
144 * The xchg implies two full memory barriers before
145 * and after, so the read-swap-read is ordered and
146 * ensures coherency with page_counter_try_charge():
147 * that function modifies the count before checking
148 * the limit, so if it sees the old limit, we see the
149 * modified counter and retry.
150 */
151 count = atomic_long_read(&counter->count);
152
153 if (count > limit)
154 return -EBUSY;
155
156 old = xchg(&counter->limit, limit);
157
158 if (atomic_long_read(&counter->count) <= count)
159 return 0;
160
161 counter->limit = old;
162 cond_resched();
163 }
164}
165
166/**
167 * page_counter_memparse - memparse() for page counter limits
168 * @buf: string to parse
Johannes Weiner650c5e52015-02-11 15:26:03 -0800169 * @max: string meaning maximum possible value
Johannes Weiner3e32cb22014-12-10 15:42:31 -0800170 * @nr_pages: returns the result in number of pages
171 *
172 * Returns -EINVAL, or 0 and @nr_pages on success. @nr_pages will be
173 * limited to %PAGE_COUNTER_MAX.
174 */
Johannes Weiner650c5e52015-02-11 15:26:03 -0800175int page_counter_memparse(const char *buf, const char *max,
176 unsigned long *nr_pages)
Johannes Weiner3e32cb22014-12-10 15:42:31 -0800177{
Johannes Weiner3e32cb22014-12-10 15:42:31 -0800178 char *end;
179 u64 bytes;
180
Johannes Weiner650c5e52015-02-11 15:26:03 -0800181 if (!strcmp(buf, max)) {
Johannes Weiner3e32cb22014-12-10 15:42:31 -0800182 *nr_pages = PAGE_COUNTER_MAX;
183 return 0;
184 }
185
186 bytes = memparse(buf, &end);
187 if (*end != '\0')
188 return -EINVAL;
189
190 *nr_pages = min(bytes / PAGE_SIZE, (u64)PAGE_COUNTER_MAX);
191
192 return 0;
193}