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git.ipfire.org Git - thirdparty/linux.git/blob - mm/page_counter.c
1 // SPDX-License-Identifier: GPL-2.0
3 * Lockless hierarchical page accounting & limiting
5 * Copyright (C) 2014 Red Hat, Inc., Johannes Weiner
8 #include <linux/page_counter.h>
9 #include <linux/atomic.h>
10 #include <linux/kernel.h>
11 #include <linux/string.h>
12 #include <linux/sched.h>
13 #include <linux/bug.h>
16 static void propagate_protected_usage(struct page_counter
*c
,
19 unsigned long protected, old_protected
;
25 protected = min(usage
, READ_ONCE(c
->min
));
26 old_protected
= atomic_long_read(&c
->min_usage
);
27 if (protected != old_protected
) {
28 old_protected
= atomic_long_xchg(&c
->min_usage
, protected);
29 delta
= protected - old_protected
;
31 atomic_long_add(delta
, &c
->parent
->children_min_usage
);
34 protected = min(usage
, READ_ONCE(c
->low
));
35 old_protected
= atomic_long_read(&c
->low_usage
);
36 if (protected != old_protected
) {
37 old_protected
= atomic_long_xchg(&c
->low_usage
, protected);
38 delta
= protected - old_protected
;
40 atomic_long_add(delta
, &c
->parent
->children_low_usage
);
45 * page_counter_cancel - take pages out of the local counter
47 * @nr_pages: number of pages to cancel
49 void page_counter_cancel(struct page_counter
*counter
, unsigned long nr_pages
)
53 new = atomic_long_sub_return(nr_pages
, &counter
->usage
);
54 /* More uncharges than charges? */
55 if (WARN_ONCE(new < 0, "page_counter underflow: %ld nr_pages=%lu\n",
58 atomic_long_set(&counter
->usage
, new);
60 propagate_protected_usage(counter
, new);
64 * page_counter_charge - hierarchically charge pages
66 * @nr_pages: number of pages to charge
68 * NOTE: This does not consider any configured counter limits.
70 void page_counter_charge(struct page_counter
*counter
, unsigned long nr_pages
)
72 struct page_counter
*c
;
74 for (c
= counter
; c
; c
= c
->parent
) {
77 new = atomic_long_add_return(nr_pages
, &c
->usage
);
78 propagate_protected_usage(c
, new);
80 * This is indeed racy, but we can live with some
81 * inaccuracy in the watermark.
83 if (new > READ_ONCE(c
->watermark
))
84 WRITE_ONCE(c
->watermark
, new);
89 * page_counter_try_charge - try to hierarchically charge pages
91 * @nr_pages: number of pages to charge
92 * @fail: points first counter to hit its limit, if any
94 * Returns %true on success, or %false and @fail if the counter or one
95 * of its ancestors has hit its configured limit.
97 bool page_counter_try_charge(struct page_counter
*counter
,
98 unsigned long nr_pages
,
99 struct page_counter
**fail
)
101 struct page_counter
*c
;
103 for (c
= counter
; c
; c
= c
->parent
) {
106 * Charge speculatively to avoid an expensive CAS. If
107 * a bigger charge fails, it might falsely lock out a
108 * racing smaller charge and send it into reclaim
109 * early, but the error is limited to the difference
110 * between the two sizes, which is less than 2M/4M in
111 * case of a THP locking out a regular page charge.
113 * The atomic_long_add_return() implies a full memory
114 * barrier between incrementing the count and reading
115 * the limit. When racing with page_counter_set_max(),
116 * we either see the new limit or the setter sees the
117 * counter has changed and retries.
119 new = atomic_long_add_return(nr_pages
, &c
->usage
);
121 atomic_long_sub(nr_pages
, &c
->usage
);
123 * This is racy, but we can live with some
124 * inaccuracy in the failcnt which is only used
127 data_race(c
->failcnt
++);
131 propagate_protected_usage(c
, new);
133 * Just like with failcnt, we can live with some
134 * inaccuracy in the watermark.
136 if (new > READ_ONCE(c
->watermark
))
137 WRITE_ONCE(c
->watermark
, new);
142 for (c
= counter
; c
!= *fail
; c
= c
->parent
)
143 page_counter_cancel(c
, nr_pages
);
149 * page_counter_uncharge - hierarchically uncharge pages
151 * @nr_pages: number of pages to uncharge
153 void page_counter_uncharge(struct page_counter
*counter
, unsigned long nr_pages
)
155 struct page_counter
*c
;
157 for (c
= counter
; c
; c
= c
->parent
)
158 page_counter_cancel(c
, nr_pages
);
162 * page_counter_set_max - set the maximum number of pages allowed
164 * @nr_pages: limit to set
166 * Returns 0 on success, -EBUSY if the current number of pages on the
167 * counter already exceeds the specified limit.
169 * The caller must serialize invocations on the same counter.
171 int page_counter_set_max(struct page_counter
*counter
, unsigned long nr_pages
)
178 * Update the limit while making sure that it's not
179 * below the concurrently-changing counter value.
181 * The xchg implies two full memory barriers before
182 * and after, so the read-swap-read is ordered and
183 * ensures coherency with page_counter_try_charge():
184 * that function modifies the count before checking
185 * the limit, so if it sees the old limit, we see the
186 * modified counter and retry.
188 usage
= page_counter_read(counter
);
190 if (usage
> nr_pages
)
193 old
= xchg(&counter
->max
, nr_pages
);
195 if (page_counter_read(counter
) <= usage
|| nr_pages
>= old
)
204 * page_counter_set_min - set the amount of protected memory
206 * @nr_pages: value to set
208 * The caller must serialize invocations on the same counter.
210 void page_counter_set_min(struct page_counter
*counter
, unsigned long nr_pages
)
212 struct page_counter
*c
;
214 WRITE_ONCE(counter
->min
, nr_pages
);
216 for (c
= counter
; c
; c
= c
->parent
)
217 propagate_protected_usage(c
, atomic_long_read(&c
->usage
));
221 * page_counter_set_low - set the amount of protected memory
223 * @nr_pages: value to set
225 * The caller must serialize invocations on the same counter.
227 void page_counter_set_low(struct page_counter
*counter
, unsigned long nr_pages
)
229 struct page_counter
*c
;
231 WRITE_ONCE(counter
->low
, nr_pages
);
233 for (c
= counter
; c
; c
= c
->parent
)
234 propagate_protected_usage(c
, atomic_long_read(&c
->usage
));
238 * page_counter_memparse - memparse() for page counter limits
239 * @buf: string to parse
240 * @max: string meaning maximum possible value
241 * @nr_pages: returns the result in number of pages
243 * Returns -EINVAL, or 0 and @nr_pages on success. @nr_pages will be
244 * limited to %PAGE_COUNTER_MAX.
246 int page_counter_memparse(const char *buf
, const char *max
,
247 unsigned long *nr_pages
)
252 if (!strcmp(buf
, max
)) {
253 *nr_pages
= PAGE_COUNTER_MAX
;
257 bytes
= memparse(buf
, &end
);
261 *nr_pages
= min(bytes
/ PAGE_SIZE
, (u64
)PAGE_COUNTER_MAX
);