v4.19.13 snapshot.
diff --git a/mm/workingset.c b/mm/workingset.c
new file mode 100644
index 0000000..4516dd7
--- /dev/null
+++ b/mm/workingset.c
@@ -0,0 +1,539 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Workingset detection
+ *
+ * Copyright (C) 2013 Red Hat, Inc., Johannes Weiner
+ */
+
+#include <linux/memcontrol.h>
+#include <linux/writeback.h>
+#include <linux/shmem_fs.h>
+#include <linux/pagemap.h>
+#include <linux/atomic.h>
+#include <linux/module.h>
+#include <linux/swap.h>
+#include <linux/dax.h>
+#include <linux/fs.h>
+#include <linux/mm.h>
+
+/*
+ * Double CLOCK lists
+ *
+ * Per node, two clock lists are maintained for file pages: the
+ * inactive and the active list. Freshly faulted pages start out at
+ * the head of the inactive list and page reclaim scans pages from the
+ * tail. Pages that are accessed multiple times on the inactive list
+ * are promoted to the active list, to protect them from reclaim,
+ * whereas active pages are demoted to the inactive list when the
+ * active list grows too big.
+ *
+ * fault ------------------------+
+ * |
+ * +--------------+ | +-------------+
+ * reclaim <- | inactive | <-+-- demotion | active | <--+
+ * +--------------+ +-------------+ |
+ * | |
+ * +-------------- promotion ------------------+
+ *
+ *
+ * Access frequency and refault distance
+ *
+ * A workload is thrashing when its pages are frequently used but they
+ * are evicted from the inactive list every time before another access
+ * would have promoted them to the active list.
+ *
+ * In cases where the average access distance between thrashing pages
+ * is bigger than the size of memory there is nothing that can be
+ * done - the thrashing set could never fit into memory under any
+ * circumstance.
+ *
+ * However, the average access distance could be bigger than the
+ * inactive list, yet smaller than the size of memory. In this case,
+ * the set could fit into memory if it weren't for the currently
+ * active pages - which may be used more, hopefully less frequently:
+ *
+ * +-memory available to cache-+
+ * | |
+ * +-inactive------+-active----+
+ * a b | c d e f g h i | J K L M N |
+ * +---------------+-----------+
+ *
+ * It is prohibitively expensive to accurately track access frequency
+ * of pages. But a reasonable approximation can be made to measure
+ * thrashing on the inactive list, after which refaulting pages can be
+ * activated optimistically to compete with the existing active pages.
+ *
+ * Approximating inactive page access frequency - Observations:
+ *
+ * 1. When a page is accessed for the first time, it is added to the
+ * head of the inactive list, slides every existing inactive page
+ * towards the tail by one slot, and pushes the current tail page
+ * out of memory.
+ *
+ * 2. When a page is accessed for the second time, it is promoted to
+ * the active list, shrinking the inactive list by one slot. This
+ * also slides all inactive pages that were faulted into the cache
+ * more recently than the activated page towards the tail of the
+ * inactive list.
+ *
+ * Thus:
+ *
+ * 1. The sum of evictions and activations between any two points in
+ * time indicate the minimum number of inactive pages accessed in
+ * between.
+ *
+ * 2. Moving one inactive page N page slots towards the tail of the
+ * list requires at least N inactive page accesses.
+ *
+ * Combining these:
+ *
+ * 1. When a page is finally evicted from memory, the number of
+ * inactive pages accessed while the page was in cache is at least
+ * the number of page slots on the inactive list.
+ *
+ * 2. In addition, measuring the sum of evictions and activations (E)
+ * at the time of a page's eviction, and comparing it to another
+ * reading (R) at the time the page faults back into memory tells
+ * the minimum number of accesses while the page was not cached.
+ * This is called the refault distance.
+ *
+ * Because the first access of the page was the fault and the second
+ * access the refault, we combine the in-cache distance with the
+ * out-of-cache distance to get the complete minimum access distance
+ * of this page:
+ *
+ * NR_inactive + (R - E)
+ *
+ * And knowing the minimum access distance of a page, we can easily
+ * tell if the page would be able to stay in cache assuming all page
+ * slots in the cache were available:
+ *
+ * NR_inactive + (R - E) <= NR_inactive + NR_active
+ *
+ * which can be further simplified to
+ *
+ * (R - E) <= NR_active
+ *
+ * Put into words, the refault distance (out-of-cache) can be seen as
+ * a deficit in inactive list space (in-cache). If the inactive list
+ * had (R - E) more page slots, the page would not have been evicted
+ * in between accesses, but activated instead. And on a full system,
+ * the only thing eating into inactive list space is active pages.
+ *
+ *
+ * Activating refaulting pages
+ *
+ * All that is known about the active list is that the pages have been
+ * accessed more than once in the past. This means that at any given
+ * time there is actually a good chance that pages on the active list
+ * are no longer in active use.
+ *
+ * So when a refault distance of (R - E) is observed and there are at
+ * least (R - E) active pages, the refaulting page is activated
+ * optimistically in the hope that (R - E) active pages are actually
+ * used less frequently than the refaulting page - or even not used at
+ * all anymore.
+ *
+ * If this is wrong and demotion kicks in, the pages which are truly
+ * used more frequently will be reactivated while the less frequently
+ * used once will be evicted from memory.
+ *
+ * But if this is right, the stale pages will be pushed out of memory
+ * and the used pages get to stay in cache.
+ *
+ *
+ * Implementation
+ *
+ * For each node's file LRU lists, a counter for inactive evictions
+ * and activations is maintained (node->inactive_age).
+ *
+ * On eviction, a snapshot of this counter (along with some bits to
+ * identify the node) is stored in the now empty page cache radix tree
+ * slot of the evicted page. This is called a shadow entry.
+ *
+ * On cache misses for which there are shadow entries, an eligible
+ * refault distance will immediately activate the refaulting page.
+ */
+
+#define EVICTION_SHIFT (RADIX_TREE_EXCEPTIONAL_ENTRY + \
+ NODES_SHIFT + \
+ MEM_CGROUP_ID_SHIFT)
+#define EVICTION_MASK (~0UL >> EVICTION_SHIFT)
+
+/*
+ * Eviction timestamps need to be able to cover the full range of
+ * actionable refaults. However, bits are tight in the radix tree
+ * entry, and after storing the identifier for the lruvec there might
+ * not be enough left to represent every single actionable refault. In
+ * that case, we have to sacrifice granularity for distance, and group
+ * evictions into coarser buckets by shaving off lower timestamp bits.
+ */
+static unsigned int bucket_order __read_mostly;
+
+static void *pack_shadow(int memcgid, pg_data_t *pgdat, unsigned long eviction)
+{
+ eviction >>= bucket_order;
+ eviction = (eviction << MEM_CGROUP_ID_SHIFT) | memcgid;
+ eviction = (eviction << NODES_SHIFT) | pgdat->node_id;
+ eviction = (eviction << RADIX_TREE_EXCEPTIONAL_SHIFT);
+
+ return (void *)(eviction | RADIX_TREE_EXCEPTIONAL_ENTRY);
+}
+
+static void unpack_shadow(void *shadow, int *memcgidp, pg_data_t **pgdat,
+ unsigned long *evictionp)
+{
+ unsigned long entry = (unsigned long)shadow;
+ int memcgid, nid;
+
+ entry >>= RADIX_TREE_EXCEPTIONAL_SHIFT;
+ nid = entry & ((1UL << NODES_SHIFT) - 1);
+ entry >>= NODES_SHIFT;
+ memcgid = entry & ((1UL << MEM_CGROUP_ID_SHIFT) - 1);
+ entry >>= MEM_CGROUP_ID_SHIFT;
+
+ *memcgidp = memcgid;
+ *pgdat = NODE_DATA(nid);
+ *evictionp = entry << bucket_order;
+}
+
+/**
+ * workingset_eviction - note the eviction of a page from memory
+ * @mapping: address space the page was backing
+ * @page: the page being evicted
+ *
+ * Returns a shadow entry to be stored in @mapping->i_pages in place
+ * of the evicted @page so that a later refault can be detected.
+ */
+void *workingset_eviction(struct address_space *mapping, struct page *page)
+{
+ struct mem_cgroup *memcg = page_memcg(page);
+ struct pglist_data *pgdat = page_pgdat(page);
+ int memcgid = mem_cgroup_id(memcg);
+ unsigned long eviction;
+ struct lruvec *lruvec;
+
+ /* Page is fully exclusive and pins page->mem_cgroup */
+ VM_BUG_ON_PAGE(PageLRU(page), page);
+ VM_BUG_ON_PAGE(page_count(page), page);
+ VM_BUG_ON_PAGE(!PageLocked(page), page);
+
+ lruvec = mem_cgroup_lruvec(pgdat, memcg);
+ eviction = atomic_long_inc_return(&lruvec->inactive_age);
+ return pack_shadow(memcgid, pgdat, eviction);
+}
+
+/**
+ * workingset_refault - evaluate the refault of a previously evicted page
+ * @shadow: shadow entry of the evicted page
+ *
+ * Calculates and evaluates the refault distance of the previously
+ * evicted page in the context of the node it was allocated in.
+ *
+ * Returns %true if the page should be activated, %false otherwise.
+ */
+bool workingset_refault(void *shadow)
+{
+ unsigned long refault_distance;
+ unsigned long active_file;
+ struct mem_cgroup *memcg;
+ unsigned long eviction;
+ struct lruvec *lruvec;
+ unsigned long refault;
+ struct pglist_data *pgdat;
+ int memcgid;
+
+ unpack_shadow(shadow, &memcgid, &pgdat, &eviction);
+
+ rcu_read_lock();
+ /*
+ * Look up the memcg associated with the stored ID. It might
+ * have been deleted since the page's eviction.
+ *
+ * Note that in rare events the ID could have been recycled
+ * for a new cgroup that refaults a shared page. This is
+ * impossible to tell from the available data. However, this
+ * should be a rare and limited disturbance, and activations
+ * are always speculative anyway. Ultimately, it's the aging
+ * algorithm's job to shake out the minimum access frequency
+ * for the active cache.
+ *
+ * XXX: On !CONFIG_MEMCG, this will always return NULL; it
+ * would be better if the root_mem_cgroup existed in all
+ * configurations instead.
+ */
+ memcg = mem_cgroup_from_id(memcgid);
+ if (!mem_cgroup_disabled() && !memcg) {
+ rcu_read_unlock();
+ return false;
+ }
+ lruvec = mem_cgroup_lruvec(pgdat, memcg);
+ refault = atomic_long_read(&lruvec->inactive_age);
+ active_file = lruvec_lru_size(lruvec, LRU_ACTIVE_FILE, MAX_NR_ZONES);
+
+ /*
+ * The unsigned subtraction here gives an accurate distance
+ * across inactive_age overflows in most cases.
+ *
+ * There is a special case: usually, shadow entries have a
+ * short lifetime and are either refaulted or reclaimed along
+ * with the inode before they get too old. But it is not
+ * impossible for the inactive_age to lap a shadow entry in
+ * the field, which can then can result in a false small
+ * refault distance, leading to a false activation should this
+ * old entry actually refault again. However, earlier kernels
+ * used to deactivate unconditionally with *every* reclaim
+ * invocation for the longest time, so the occasional
+ * inappropriate activation leading to pressure on the active
+ * list is not a problem.
+ */
+ refault_distance = (refault - eviction) & EVICTION_MASK;
+
+ inc_lruvec_state(lruvec, WORKINGSET_REFAULT);
+
+ if (refault_distance <= active_file) {
+ inc_lruvec_state(lruvec, WORKINGSET_ACTIVATE);
+ rcu_read_unlock();
+ return true;
+ }
+ rcu_read_unlock();
+ return false;
+}
+
+/**
+ * workingset_activation - note a page activation
+ * @page: page that is being activated
+ */
+void workingset_activation(struct page *page)
+{
+ struct mem_cgroup *memcg;
+ struct lruvec *lruvec;
+
+ rcu_read_lock();
+ /*
+ * Filter non-memcg pages here, e.g. unmap can call
+ * mark_page_accessed() on VDSO pages.
+ *
+ * XXX: See workingset_refault() - this should return
+ * root_mem_cgroup even for !CONFIG_MEMCG.
+ */
+ memcg = page_memcg_rcu(page);
+ if (!mem_cgroup_disabled() && !memcg)
+ goto out;
+ lruvec = mem_cgroup_lruvec(page_pgdat(page), memcg);
+ atomic_long_inc(&lruvec->inactive_age);
+out:
+ rcu_read_unlock();
+}
+
+/*
+ * Shadow entries reflect the share of the working set that does not
+ * fit into memory, so their number depends on the access pattern of
+ * the workload. In most cases, they will refault or get reclaimed
+ * along with the inode, but a (malicious) workload that streams
+ * through files with a total size several times that of available
+ * memory, while preventing the inodes from being reclaimed, can
+ * create excessive amounts of shadow nodes. To keep a lid on this,
+ * track shadow nodes and reclaim them when they grow way past the
+ * point where they would still be useful.
+ */
+
+static struct list_lru shadow_nodes;
+
+void workingset_update_node(struct radix_tree_node *node)
+{
+ /*
+ * Track non-empty nodes that contain only shadow entries;
+ * unlink those that contain pages or are being freed.
+ *
+ * Avoid acquiring the list_lru lock when the nodes are
+ * already where they should be. The list_empty() test is safe
+ * as node->private_list is protected by the i_pages lock.
+ */
+ if (node->count && node->count == node->exceptional) {
+ if (list_empty(&node->private_list))
+ list_lru_add(&shadow_nodes, &node->private_list);
+ } else {
+ if (!list_empty(&node->private_list))
+ list_lru_del(&shadow_nodes, &node->private_list);
+ }
+}
+
+static unsigned long count_shadow_nodes(struct shrinker *shrinker,
+ struct shrink_control *sc)
+{
+ unsigned long max_nodes;
+ unsigned long nodes;
+ unsigned long cache;
+
+ nodes = list_lru_shrink_count(&shadow_nodes, sc);
+
+ /*
+ * Approximate a reasonable limit for the radix tree nodes
+ * containing shadow entries. We don't need to keep more
+ * shadow entries than possible pages on the active list,
+ * since refault distances bigger than that are dismissed.
+ *
+ * The size of the active list converges toward 100% of
+ * overall page cache as memory grows, with only a tiny
+ * inactive list. Assume the total cache size for that.
+ *
+ * Nodes might be sparsely populated, with only one shadow
+ * entry in the extreme case. Obviously, we cannot keep one
+ * node for every eligible shadow entry, so compromise on a
+ * worst-case density of 1/8th. Below that, not all eligible
+ * refaults can be detected anymore.
+ *
+ * On 64-bit with 7 radix_tree_nodes per page and 64 slots
+ * each, this will reclaim shadow entries when they consume
+ * ~1.8% of available memory:
+ *
+ * PAGE_SIZE / radix_tree_nodes / node_entries * 8 / PAGE_SIZE
+ */
+ if (sc->memcg) {
+ cache = mem_cgroup_node_nr_lru_pages(sc->memcg, sc->nid,
+ LRU_ALL_FILE);
+ } else {
+ cache = node_page_state(NODE_DATA(sc->nid), NR_ACTIVE_FILE) +
+ node_page_state(NODE_DATA(sc->nid), NR_INACTIVE_FILE);
+ }
+ max_nodes = cache >> (RADIX_TREE_MAP_SHIFT - 3);
+
+ if (!nodes)
+ return SHRINK_EMPTY;
+
+ if (nodes <= max_nodes)
+ return 0;
+ return nodes - max_nodes;
+}
+
+static enum lru_status shadow_lru_isolate(struct list_head *item,
+ struct list_lru_one *lru,
+ spinlock_t *lru_lock,
+ void *arg)
+{
+ struct address_space *mapping;
+ struct radix_tree_node *node;
+ unsigned int i;
+ int ret;
+
+ /*
+ * Page cache insertions and deletions synchroneously maintain
+ * the shadow node LRU under the i_pages lock and the
+ * lru_lock. Because the page cache tree is emptied before
+ * the inode can be destroyed, holding the lru_lock pins any
+ * address_space that has radix tree nodes on the LRU.
+ *
+ * We can then safely transition to the i_pages lock to
+ * pin only the address_space of the particular node we want
+ * to reclaim, take the node off-LRU, and drop the lru_lock.
+ */
+
+ node = container_of(item, struct radix_tree_node, private_list);
+ mapping = container_of(node->root, struct address_space, i_pages);
+
+ /* Coming from the list, invert the lock order */
+ if (!xa_trylock(&mapping->i_pages)) {
+ spin_unlock_irq(lru_lock);
+ ret = LRU_RETRY;
+ goto out;
+ }
+
+ list_lru_isolate(lru, item);
+ spin_unlock(lru_lock);
+
+ /*
+ * The nodes should only contain one or more shadow entries,
+ * no pages, so we expect to be able to remove them all and
+ * delete and free the empty node afterwards.
+ */
+ if (WARN_ON_ONCE(!node->exceptional))
+ goto out_invalid;
+ if (WARN_ON_ONCE(node->count != node->exceptional))
+ goto out_invalid;
+ for (i = 0; i < RADIX_TREE_MAP_SIZE; i++) {
+ if (node->slots[i]) {
+ if (WARN_ON_ONCE(!radix_tree_exceptional_entry(node->slots[i])))
+ goto out_invalid;
+ if (WARN_ON_ONCE(!node->exceptional))
+ goto out_invalid;
+ if (WARN_ON_ONCE(!mapping->nrexceptional))
+ goto out_invalid;
+ node->slots[i] = NULL;
+ node->exceptional--;
+ node->count--;
+ mapping->nrexceptional--;
+ }
+ }
+ if (WARN_ON_ONCE(node->exceptional))
+ goto out_invalid;
+ inc_lruvec_page_state(virt_to_page(node), WORKINGSET_NODERECLAIM);
+ __radix_tree_delete_node(&mapping->i_pages, node,
+ workingset_lookup_update(mapping));
+
+out_invalid:
+ xa_unlock_irq(&mapping->i_pages);
+ ret = LRU_REMOVED_RETRY;
+out:
+ cond_resched();
+ spin_lock_irq(lru_lock);
+ return ret;
+}
+
+static unsigned long scan_shadow_nodes(struct shrinker *shrinker,
+ struct shrink_control *sc)
+{
+ /* list_lru lock nests inside the IRQ-safe i_pages lock */
+ return list_lru_shrink_walk_irq(&shadow_nodes, sc, shadow_lru_isolate,
+ NULL);
+}
+
+static struct shrinker workingset_shadow_shrinker = {
+ .count_objects = count_shadow_nodes,
+ .scan_objects = scan_shadow_nodes,
+ .seeks = DEFAULT_SEEKS,
+ .flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE,
+};
+
+/*
+ * Our list_lru->lock is IRQ-safe as it nests inside the IRQ-safe
+ * i_pages lock.
+ */
+static struct lock_class_key shadow_nodes_key;
+
+static int __init workingset_init(void)
+{
+ unsigned int timestamp_bits;
+ unsigned int max_order;
+ int ret;
+
+ BUILD_BUG_ON(BITS_PER_LONG < EVICTION_SHIFT);
+ /*
+ * Calculate the eviction bucket size to cover the longest
+ * actionable refault distance, which is currently half of
+ * memory (totalram_pages/2). However, memory hotplug may add
+ * some more pages at runtime, so keep working with up to
+ * double the initial memory by using totalram_pages as-is.
+ */
+ timestamp_bits = BITS_PER_LONG - EVICTION_SHIFT;
+ max_order = fls_long(totalram_pages - 1);
+ if (max_order > timestamp_bits)
+ bucket_order = max_order - timestamp_bits;
+ pr_info("workingset: timestamp_bits=%d max_order=%d bucket_order=%u\n",
+ timestamp_bits, max_order, bucket_order);
+
+ ret = prealloc_shrinker(&workingset_shadow_shrinker);
+ if (ret)
+ goto err;
+ ret = __list_lru_init(&shadow_nodes, true, &shadow_nodes_key,
+ &workingset_shadow_shrinker);
+ if (ret)
+ goto err_list_lru;
+ register_shrinker_prepared(&workingset_shadow_shrinker);
+ return 0;
+err_list_lru:
+ free_prealloced_shrinker(&workingset_shadow_shrinker);
+err:
+ return ret;
+}
+module_init(workingset_init);