1 files changed, 465 insertions, 0 deletions
diff --git a/mm/page_counter.c b/mm/page_counter.c
new file mode 100644
index 000000000000..661e0f2a5127
--- /dev/null
+++ b/mm/page_counter.c
@@ -0,0 +1,465 @@
+// 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 bool track_protection(struct page_counter *c)
+{
+	return c->protection_support;
+}
+
+static void propagate_protected_usage(struct page_counter *c,
+				      unsigned long usage)
+{
+	unsigned long protected, old_protected;
+	long delta;
+
+	if (!c->parent)
+		return;
+
+	protected = min(usage, READ_ONCE(c->min));
+	old_protected = atomic_long_read(&c->min_usage);
+	if (protected != old_protected) {
+		old_protected = atomic_long_xchg(&c->min_usage, protected);
+		delta = protected - old_protected;
+		if (delta)
+			atomic_long_add(delta, &c->parent->children_min_usage);
+	}
+
+	protected = min(usage, READ_ONCE(c->low));
+	old_protected = atomic_long_read(&c->low_usage);
+	if (protected != old_protected) {
+		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);
+	/* More uncharges than charges? */
+	if (WARN_ONCE(new < 0, "page_counter underflow: %ld nr_pages=%lu\n",
+		      new, nr_pages)) {
+		new = 0;
+		atomic_long_set(&counter->usage, new);
+	}
+	if (track_protection(counter))
+		propagate_protected_usage(counter, new);
+}
+
+/**
+ * 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;
+	bool protection = track_protection(counter);
+
+	for (c = counter; c; c = c->parent) {
+		long new;
+
+		new = atomic_long_add_return(nr_pages, &c->usage);
+		if (protection)
+			propagate_protected_usage(c, new);
+		/*
+		 * This is indeed racy, but we can live with some
+		 * inaccuracy in the watermark.
+		 *
+		 * Notably, we have two watermarks to allow for both a globally
+		 * visible peak and one that can be reset at a smaller scope.
+		 *
+		 * Since we reset both watermarks when the global reset occurs,
+		 * we can guarantee that watermark >= local_watermark, so we
+		 * don't need to do both comparisons every time.
+		 *
+		 * On systems with branch predictors, the inner condition should
+		 * be almost free.
+		 */
+		if (new > READ_ONCE(c->local_watermark)) {
+			WRITE_ONCE(c->local_watermark, new);
+			if (new > READ_ONCE(c->watermark))
+				WRITE_ONCE(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;
+	bool protection = track_protection(counter);
+	bool track_failcnt = counter->track_failcnt;
+
+	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_set_max(),
+		 * 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);
+			/*
+			 * This is racy, but we can live with some
+			 * inaccuracy in the failcnt which is only used
+			 * to report stats.
+			 */
+			if (track_failcnt)
+				data_race(c->failcnt++);
+			*fail = c;
+			goto failed;
+		}
+		if (protection)
+			propagate_protected_usage(c, new);
+
+		/* see comment on page_counter_charge */
+		if (new > READ_ONCE(c->local_watermark)) {
+			WRITE_ONCE(c->local_watermark, new);
+			if (new > READ_ONCE(c->watermark))
+				WRITE_ONCE(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 = page_counter_read(counter);
+
+		if (usage > nr_pages)
+			return -EBUSY;
+
+		old = xchg(&counter->max, nr_pages);
+
+		if (page_counter_read(counter) <= usage || nr_pages >= old)
+			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;
+
+	WRITE_ONCE(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;
+
+	WRITE_ONCE(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;
+}
+
+
+#if IS_ENABLED(CONFIG_MEMCG) || IS_ENABLED(CONFIG_CGROUP_DMEM)
+/*
+ * This function calculates an individual page counter's effective
+ * protection which is derived from its own memory.min/low, its
+ * parent's and siblings' settings, as well as the actual memory
+ * distribution in the tree.
+ *
+ * The following rules apply to the effective protection values:
+ *
+ * 1. At the first level of reclaim, effective protection is equal to
+ *    the declared protection in memory.min and memory.low.
+ *
+ * 2. To enable safe delegation of the protection configuration, at
+ *    subsequent levels the effective protection is capped to the
+ *    parent's effective protection.
+ *
+ * 3. To make complex and dynamic subtrees easier to configure, the
+ *    user is allowed to overcommit the declared protection at a given
+ *    level. If that is the case, the parent's effective protection is
+ *    distributed to the children in proportion to how much protection
+ *    they have declared and how much of it they are utilizing.
+ *
+ *    This makes distribution proportional, but also work-conserving:
+ *    if one counter claims much more protection than it uses memory,
+ *    the unused remainder is available to its siblings.
+ *
+ * 4. Conversely, when the declared protection is undercommitted at a
+ *    given level, the distribution of the larger parental protection
+ *    budget is NOT proportional. A counter's protection from a sibling
+ *    is capped to its own memory.min/low setting.
+ *
+ * 5. However, to allow protecting recursive subtrees from each other
+ *    without having to declare each individual counter's fixed share
+ *    of the ancestor's claim to protection, any unutilized -
+ *    "floating" - protection from up the tree is distributed in
+ *    proportion to each counter's *usage*. This makes the protection
+ *    neutral wrt sibling cgroups and lets them compete freely over
+ *    the shared parental protection budget, but it protects the
+ *    subtree as a whole from neighboring subtrees.
+ *
+ * Note that 4. and 5. are not in conflict: 4. is about protecting
+ * against immediate siblings whereas 5. is about protecting against
+ * neighboring subtrees.
+ */
+static unsigned long effective_protection(unsigned long usage,
+					  unsigned long parent_usage,
+					  unsigned long setting,
+					  unsigned long parent_effective,
+					  unsigned long siblings_protected,
+					  bool recursive_protection)
+{
+	unsigned long protected;
+	unsigned long ep;
+
+	protected = min(usage, setting);
+	/*
+	 * If all cgroups at this level combined claim and use more
+	 * protection than what the parent affords them, distribute
+	 * shares in proportion to utilization.
+	 *
+	 * We are using actual utilization rather than the statically
+	 * claimed protection in order to be work-conserving: claimed
+	 * but unused protection is available to siblings that would
+	 * otherwise get a smaller chunk than what they claimed.
+	 */
+	if (siblings_protected > parent_effective)
+		return protected * parent_effective / siblings_protected;
+
+	/*
+	 * Ok, utilized protection of all children is within what the
+	 * parent affords them, so we know whatever this child claims
+	 * and utilizes is effectively protected.
+	 *
+	 * If there is unprotected usage beyond this value, reclaim
+	 * will apply pressure in proportion to that amount.
+	 *
+	 * If there is unutilized protection, the cgroup will be fully
+	 * shielded from reclaim, but we do return a smaller value for
+	 * protection than what the group could enjoy in theory. This
+	 * is okay. With the overcommit distribution above, effective
+	 * protection is always dependent on how memory is actually
+	 * consumed among the siblings anyway.
+	 */
+	ep = protected;
+
+	/*
+	 * If the children aren't claiming (all of) the protection
+	 * afforded to them by the parent, distribute the remainder in
+	 * proportion to the (unprotected) memory of each cgroup. That
+	 * way, cgroups that aren't explicitly prioritized wrt each
+	 * other compete freely over the allowance, but they are
+	 * collectively protected from neighboring trees.
+	 *
+	 * We're using unprotected memory for the weight so that if
+	 * some cgroups DO claim explicit protection, we don't protect
+	 * the same bytes twice.
+	 *
+	 * Check both usage and parent_usage against the respective
+	 * protected values. One should imply the other, but they
+	 * aren't read atomically - make sure the division is sane.
+	 */
+	if (!recursive_protection)
+		return ep;
+
+	if (parent_effective > siblings_protected &&
+	    parent_usage > siblings_protected &&
+	    usage > protected) {
+		unsigned long unclaimed;
+
+		unclaimed = parent_effective - siblings_protected;
+		unclaimed *= usage - protected;
+		unclaimed /= parent_usage - siblings_protected;
+
+		ep += unclaimed;
+	}
+
+	return ep;
+}
+
+
+/**
+ * page_counter_calculate_protection - check if memory consumption is in the normal range
+ * @root: the top ancestor of the sub-tree being checked
+ * @counter: the page_counter the counter to update
+ * @recursive_protection: Whether to use memory_recursiveprot behavior.
+ *
+ * Calculates elow/emin thresholds for given page_counter.
+ *
+ * WARNING: This function is not stateless! It can only be used as part
+ *          of a top-down tree iteration, not for isolated queries.
+ */
+void page_counter_calculate_protection(struct page_counter *root,
+				       struct page_counter *counter,
+				       bool recursive_protection)
+{
+	unsigned long usage, parent_usage;
+	struct page_counter *parent = counter->parent;
+
+	/*
+	 * Effective values of the reclaim targets are ignored so they
+	 * can be stale. Have a look at mem_cgroup_protection for more
+	 * details.
+	 * TODO: calculation should be more robust so that we do not need
+	 * that special casing.
+	 */
+	if (root == counter)
+		return;
+
+	usage = page_counter_read(counter);
+	if (!usage)
+		return;
+
+	if (parent == root) {
+		counter->emin = READ_ONCE(counter->min);
+		counter->elow = READ_ONCE(counter->low);
+		return;
+	}
+
+	parent_usage = page_counter_read(parent);
+
+	WRITE_ONCE(counter->emin, effective_protection(usage, parent_usage,
+			READ_ONCE(counter->min),
+			READ_ONCE(parent->emin),
+			atomic_long_read(&parent->children_min_usage),
+			recursive_protection));
+
+	WRITE_ONCE(counter->elow, effective_protection(usage, parent_usage,
+			READ_ONCE(counter->low),
+			READ_ONCE(parent->elow),
+			atomic_long_read(&parent->children_low_usage),
+			recursive_protection));
+}
+#endif /* CONFIG_MEMCG || CONFIG_CGROUP_DMEM */