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Diffstat (limited to '')
-rw-r--r-- | mm/page_counter.c | 266 |
1 files changed, 266 insertions, 0 deletions
diff --git a/mm/page_counter.c b/mm/page_counter.c new file mode 100644 index 000000000..147ff9918 --- /dev/null +++ b/mm/page_counter.c @@ -0,0 +1,266 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Lockless hierarchical page accounting & limiting + * + * Copyright (C) 2014 Red Hat, Inc., Johannes Weiner + */ + +#include <linux/page_counter.h> +#include <linux/atomic.h> +#include <linux/kernel.h> +#include <linux/string.h> +#include <linux/sched.h> +#include <linux/bug.h> +#include <asm/page.h> + +static void propagate_protected_usage(struct page_counter *c, + unsigned long usage) +{ + unsigned long protected, old_protected; + long delta; + + if (!c->parent) + return; + + if (c->min || atomic_long_read(&c->min_usage)) { + if (usage <= c->min) + protected = usage; + else + protected = 0; + + old_protected = atomic_long_xchg(&c->min_usage, protected); + delta = protected - old_protected; + if (delta) + atomic_long_add(delta, &c->parent->children_min_usage); + } + + if (c->low || atomic_long_read(&c->low_usage)) { + if (usage <= c->low) + protected = usage; + else + protected = 0; + + old_protected = atomic_long_xchg(&c->low_usage, protected); + delta = protected - old_protected; + if (delta) + atomic_long_add(delta, &c->parent->children_low_usage); + } +} + +/** + * page_counter_cancel - take pages out of the local counter + * @counter: counter + * @nr_pages: number of pages to cancel + */ +void page_counter_cancel(struct page_counter *counter, unsigned long nr_pages) +{ + long new; + + new = atomic_long_sub_return(nr_pages, &counter->usage); + propagate_protected_usage(counter, new); + /* More uncharges than charges? */ + WARN_ON_ONCE(new < 0); +} + +/** + * page_counter_charge - hierarchically charge pages + * @counter: counter + * @nr_pages: number of pages to charge + * + * NOTE: This does not consider any configured counter limits. + */ +void page_counter_charge(struct page_counter *counter, unsigned long nr_pages) +{ + struct page_counter *c; + + for (c = counter; c; c = c->parent) { + long new; + + new = atomic_long_add_return(nr_pages, &c->usage); + propagate_protected_usage(c, new); + /* + * This is indeed racy, but we can live with some + * inaccuracy in the watermark. + */ + if (new > c->watermark) + c->watermark = new; + } +} + +/** + * page_counter_try_charge - try to hierarchically charge pages + * @counter: counter + * @nr_pages: number of pages to charge + * @fail: points first counter to hit its limit, if any + * + * Returns %true on success, or %false and @fail if the counter or one + * of its ancestors has hit its configured limit. + */ +bool page_counter_try_charge(struct page_counter *counter, + unsigned long nr_pages, + struct page_counter **fail) +{ + struct page_counter *c; + + for (c = counter; c; c = c->parent) { + long new; + /* + * Charge speculatively to avoid an expensive CAS. If + * a bigger charge fails, it might falsely lock out a + * racing smaller charge and send it into reclaim + * early, but the error is limited to the difference + * between the two sizes, which is less than 2M/4M in + * case of a THP locking out a regular page charge. + * + * The atomic_long_add_return() implies a full memory + * barrier between incrementing the count and reading + * the limit. When racing with page_counter_limit(), + * we either see the new limit or the setter sees the + * counter has changed and retries. + */ + new = atomic_long_add_return(nr_pages, &c->usage); + if (new > c->max) { + atomic_long_sub(nr_pages, &c->usage); + propagate_protected_usage(c, new); + /* + * This is racy, but we can live with some + * inaccuracy in the failcnt. + */ + c->failcnt++; + *fail = c; + goto failed; + } + propagate_protected_usage(c, new); + /* + * Just like with failcnt, we can live with some + * inaccuracy in the watermark. + */ + if (new > c->watermark) + c->watermark = new; + } + return true; + +failed: + for (c = counter; c != *fail; c = c->parent) + page_counter_cancel(c, nr_pages); + + return false; +} + +/** + * page_counter_uncharge - hierarchically uncharge pages + * @counter: counter + * @nr_pages: number of pages to uncharge + */ +void page_counter_uncharge(struct page_counter *counter, unsigned long nr_pages) +{ + struct page_counter *c; + + for (c = counter; c; c = c->parent) + page_counter_cancel(c, nr_pages); +} + +/** + * page_counter_set_max - set the maximum number of pages allowed + * @counter: counter + * @nr_pages: limit to set + * + * Returns 0 on success, -EBUSY if the current number of pages on the + * counter already exceeds the specified limit. + * + * The caller must serialize invocations on the same counter. + */ +int page_counter_set_max(struct page_counter *counter, unsigned long nr_pages) +{ + for (;;) { + unsigned long old; + long usage; + + /* + * Update the limit while making sure that it's not + * below the concurrently-changing counter value. + * + * The xchg implies two full memory barriers before + * and after, so the read-swap-read is ordered and + * ensures coherency with page_counter_try_charge(): + * that function modifies the count before checking + * the limit, so if it sees the old limit, we see the + * modified counter and retry. + */ + usage = atomic_long_read(&counter->usage); + + if (usage > nr_pages) + return -EBUSY; + + old = xchg(&counter->max, nr_pages); + + if (atomic_long_read(&counter->usage) <= usage) + return 0; + + counter->max = old; + cond_resched(); + } +} + +/** + * page_counter_set_min - set the amount of protected memory + * @counter: counter + * @nr_pages: value to set + * + * The caller must serialize invocations on the same counter. + */ +void page_counter_set_min(struct page_counter *counter, unsigned long nr_pages) +{ + struct page_counter *c; + + counter->min = nr_pages; + + for (c = counter; c; c = c->parent) + propagate_protected_usage(c, atomic_long_read(&c->usage)); +} + +/** + * page_counter_set_low - set the amount of protected memory + * @counter: counter + * @nr_pages: value to set + * + * The caller must serialize invocations on the same counter. + */ +void page_counter_set_low(struct page_counter *counter, unsigned long nr_pages) +{ + struct page_counter *c; + + counter->low = nr_pages; + + for (c = counter; c; c = c->parent) + propagate_protected_usage(c, atomic_long_read(&c->usage)); +} + +/** + * page_counter_memparse - memparse() for page counter limits + * @buf: string to parse + * @max: string meaning maximum possible value + * @nr_pages: returns the result in number of pages + * + * Returns -EINVAL, or 0 and @nr_pages on success. @nr_pages will be + * limited to %PAGE_COUNTER_MAX. + */ +int page_counter_memparse(const char *buf, const char *max, + unsigned long *nr_pages) +{ + char *end; + u64 bytes; + + if (!strcmp(buf, max)) { + *nr_pages = PAGE_COUNTER_MAX; + return 0; + } + + bytes = memparse(buf, &end); + if (*end != '\0') + return -EINVAL; + + *nr_pages = min(bytes / PAGE_SIZE, (u64)PAGE_COUNTER_MAX); + + return 0; +} |