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1/*
2 * Workingset detection
3 *
4 * Copyright (C) 2013 Red Hat, Inc., Johannes Weiner
5 */
6
7#include <linux/memcontrol.h>
8#include <linux/writeback.h>
9#include <linux/pagemap.h>
10#include <linux/atomic.h>
11#include <linux/module.h>
12#include <linux/swap.h>
13#include <linux/fs.h>
14#include <linux/mm.h>
15
16/*
17 * Double CLOCK lists
18 *
19 * Per zone, two clock lists are maintained for file pages: the
20 * inactive and the active list. Freshly faulted pages start out at
21 * the head of the inactive list and page reclaim scans pages from the
22 * tail. Pages that are accessed multiple times on the inactive list
23 * are promoted to the active list, to protect them from reclaim,
24 * whereas active pages are demoted to the inactive list when the
25 * active list grows too big.
26 *
27 * fault ------------------------+
28 * |
29 * +--------------+ | +-------------+
30 * reclaim <- | inactive | <-+-- demotion | active | <--+
31 * +--------------+ +-------------+ |
32 * | |
33 * +-------------- promotion ------------------+
34 *
35 *
36 * Access frequency and refault distance
37 *
38 * A workload is thrashing when its pages are frequently used but they
39 * are evicted from the inactive list every time before another access
40 * would have promoted them to the active list.
41 *
42 * In cases where the average access distance between thrashing pages
43 * is bigger than the size of memory there is nothing that can be
44 * done - the thrashing set could never fit into memory under any
45 * circumstance.
46 *
47 * However, the average access distance could be bigger than the
48 * inactive list, yet smaller than the size of memory. In this case,
49 * the set could fit into memory if it weren't for the currently
50 * active pages - which may be used more, hopefully less frequently:
51 *
52 * +-memory available to cache-+
53 * | |
54 * +-inactive------+-active----+
55 * a b | c d e f g h i | J K L M N |
56 * +---------------+-----------+
57 *
58 * It is prohibitively expensive to accurately track access frequency
59 * of pages. But a reasonable approximation can be made to measure
60 * thrashing on the inactive list, after which refaulting pages can be
61 * activated optimistically to compete with the existing active pages.
62 *
63 * Approximating inactive page access frequency - Observations:
64 *
65 * 1. When a page is accessed for the first time, it is added to the
66 * head of the inactive list, slides every existing inactive page
67 * towards the tail by one slot, and pushes the current tail page
68 * out of memory.
69 *
70 * 2. When a page is accessed for the second time, it is promoted to
71 * the active list, shrinking the inactive list by one slot. This
72 * also slides all inactive pages that were faulted into the cache
73 * more recently than the activated page towards the tail of the
74 * inactive list.
75 *
76 * Thus:
77 *
78 * 1. The sum of evictions and activations between any two points in
79 * time indicate the minimum number of inactive pages accessed in
80 * between.
81 *
82 * 2. Moving one inactive page N page slots towards the tail of the
83 * list requires at least N inactive page accesses.
84 *
85 * Combining these:
86 *
87 * 1. When a page is finally evicted from memory, the number of
88 * inactive pages accessed while the page was in cache is at least
89 * the number of page slots on the inactive list.
90 *
91 * 2. In addition, measuring the sum of evictions and activations (E)
92 * at the time of a page's eviction, and comparing it to another
93 * reading (R) at the time the page faults back into memory tells
94 * the minimum number of accesses while the page was not cached.
95 * This is called the refault distance.
96 *
97 * Because the first access of the page was the fault and the second
98 * access the refault, we combine the in-cache distance with the
99 * out-of-cache distance to get the complete minimum access distance
100 * of this page:
101 *
102 * NR_inactive + (R - E)
103 *
104 * And knowing the minimum access distance of a page, we can easily
105 * tell if the page would be able to stay in cache assuming all page
106 * slots in the cache were available:
107 *
108 * NR_inactive + (R - E) <= NR_inactive + NR_active
109 *
110 * which can be further simplified to
111 *
112 * (R - E) <= NR_active
113 *
114 * Put into words, the refault distance (out-of-cache) can be seen as
115 * a deficit in inactive list space (in-cache). If the inactive list
116 * had (R - E) more page slots, the page would not have been evicted
117 * in between accesses, but activated instead. And on a full system,
118 * the only thing eating into inactive list space is active pages.
119 *
120 *
121 * Activating refaulting pages
122 *
123 * All that is known about the active list is that the pages have been
124 * accessed more than once in the past. This means that at any given
125 * time there is actually a good chance that pages on the active list
126 * are no longer in active use.
127 *
128 * So when a refault distance of (R - E) is observed and there are at
129 * least (R - E) active pages, the refaulting page is activated
130 * optimistically in the hope that (R - E) active pages are actually
131 * used less frequently than the refaulting page - or even not used at
132 * all anymore.
133 *
134 * If this is wrong and demotion kicks in, the pages which are truly
135 * used more frequently will be reactivated while the less frequently
136 * used once will be evicted from memory.
137 *
138 * But if this is right, the stale pages will be pushed out of memory
139 * and the used pages get to stay in cache.
140 *
141 *
142 * Implementation
143 *
144 * For each zone's file LRU lists, a counter for inactive evictions
145 * and activations is maintained (zone->inactive_age).
146 *
147 * On eviction, a snapshot of this counter (along with some bits to
148 * identify the zone) is stored in the now empty page cache radix tree
149 * slot of the evicted page. This is called a shadow entry.
150 *
151 * On cache misses for which there are shadow entries, an eligible
152 * refault distance will immediately activate the refaulting page.
153 */
154
155static void *pack_shadow(unsigned long eviction, struct zone *zone)
156{
157 eviction = (eviction << NODES_SHIFT) | zone_to_nid(zone);
158 eviction = (eviction << ZONES_SHIFT) | zone_idx(zone);
159 eviction = (eviction << RADIX_TREE_EXCEPTIONAL_SHIFT);
160
161 return (void *)(eviction | RADIX_TREE_EXCEPTIONAL_ENTRY);
162}
163
164static void unpack_shadow(void *shadow,
165 struct zone **zone,
166 unsigned long *distance)
167{
168 unsigned long entry = (unsigned long)shadow;
169 unsigned long eviction;
170 unsigned long refault;
171 unsigned long mask;
172 int zid, nid;
173
174 entry >>= RADIX_TREE_EXCEPTIONAL_SHIFT;
175 zid = entry & ((1UL << ZONES_SHIFT) - 1);
176 entry >>= ZONES_SHIFT;
177 nid = entry & ((1UL << NODES_SHIFT) - 1);
178 entry >>= NODES_SHIFT;
179 eviction = entry;
180
181 *zone = NODE_DATA(nid)->node_zones + zid;
182
183 refault = atomic_long_read(&(*zone)->inactive_age);
184 mask = ~0UL >> (NODES_SHIFT + ZONES_SHIFT +
185 RADIX_TREE_EXCEPTIONAL_SHIFT);
186 /*
187 * The unsigned subtraction here gives an accurate distance
188 * across inactive_age overflows in most cases.
189 *
190 * There is a special case: usually, shadow entries have a
191 * short lifetime and are either refaulted or reclaimed along
192 * with the inode before they get too old. But it is not
193 * impossible for the inactive_age to lap a shadow entry in
194 * the field, which can then can result in a false small
195 * refault distance, leading to a false activation should this
196 * old entry actually refault again. However, earlier kernels
197 * used to deactivate unconditionally with *every* reclaim
198 * invocation for the longest time, so the occasional
199 * inappropriate activation leading to pressure on the active
200 * list is not a problem.
201 */
202 *distance = (refault - eviction) & mask;
203}
204
205/**
206 * workingset_eviction - note the eviction of a page from memory
207 * @mapping: address space the page was backing
208 * @page: the page being evicted
209 *
210 * Returns a shadow entry to be stored in @mapping->page_tree in place
211 * of the evicted @page so that a later refault can be detected.
212 */
213void *workingset_eviction(struct address_space *mapping, struct page *page)
214{
215 struct zone *zone = page_zone(page);
216 unsigned long eviction;
217
218 eviction = atomic_long_inc_return(&zone->inactive_age);
219 return pack_shadow(eviction, zone);
220}
221
222/**
223 * workingset_refault - evaluate the refault of a previously evicted page
224 * @shadow: shadow entry of the evicted page
225 *
226 * Calculates and evaluates the refault distance of the previously
227 * evicted page in the context of the zone it was allocated in.
228 *
229 * Returns %true if the page should be activated, %false otherwise.
230 */
231bool workingset_refault(void *shadow)
232{
233 unsigned long refault_distance;
234 struct zone *zone;
235
236 unpack_shadow(shadow, &zone, &refault_distance);
237 inc_zone_state(zone, WORKINGSET_REFAULT);
238
239 if (refault_distance <= zone_page_state(zone, NR_ACTIVE_FILE)) {
240 inc_zone_state(zone, WORKINGSET_ACTIVATE);
241 return true;
242 }
243 return false;
244}
245
246/**
247 * workingset_activation - note a page activation
248 * @page: page that is being activated
249 */
250void workingset_activation(struct page *page)
251{
252 atomic_long_inc(&page_zone(page)->inactive_age);
253}
254
255/*
256 * Shadow entries reflect the share of the working set that does not
257 * fit into memory, so their number depends on the access pattern of
258 * the workload. In most cases, they will refault or get reclaimed
259 * along with the inode, but a (malicious) workload that streams
260 * through files with a total size several times that of available
261 * memory, while preventing the inodes from being reclaimed, can
262 * create excessive amounts of shadow nodes. To keep a lid on this,
263 * track shadow nodes and reclaim them when they grow way past the
264 * point where they would still be useful.
265 */
266
267struct list_lru workingset_shadow_nodes;
268
269static unsigned long count_shadow_nodes(struct shrinker *shrinker,
270 struct shrink_control *sc)
271{
272 unsigned long shadow_nodes;
273 unsigned long max_nodes;
274 unsigned long pages;
275
276 /* list_lru lock nests inside IRQ-safe mapping->tree_lock */
277 local_irq_disable();
278 shadow_nodes = list_lru_count_node(&workingset_shadow_nodes, sc->nid);
279 local_irq_enable();
280
281 pages = node_present_pages(sc->nid);
282 /*
283 * Active cache pages are limited to 50% of memory, and shadow
284 * entries that represent a refault distance bigger than that
285 * do not have any effect. Limit the number of shadow nodes
286 * such that shadow entries do not exceed the number of active
287 * cache pages, assuming a worst-case node population density
288 * of 1/8th on average.
289 *
290 * On 64-bit with 7 radix_tree_nodes per page and 64 slots
291 * each, this will reclaim shadow entries when they consume
292 * ~2% of available memory:
293 *
294 * PAGE_SIZE / radix_tree_nodes / node_entries / PAGE_SIZE
295 */
296 max_nodes = pages >> (1 + RADIX_TREE_MAP_SHIFT - 3);
297
298 if (shadow_nodes <= max_nodes)
299 return 0;
300
301 return shadow_nodes - max_nodes;
302}
303
304static enum lru_status shadow_lru_isolate(struct list_head *item,
305 spinlock_t *lru_lock,
306 void *arg)
307{
308 struct address_space *mapping;
309 struct radix_tree_node *node;
310 unsigned int i;
311 int ret;
312
313 /*
314 * Page cache insertions and deletions synchroneously maintain
315 * the shadow node LRU under the mapping->tree_lock and the
316 * lru_lock. Because the page cache tree is emptied before
317 * the inode can be destroyed, holding the lru_lock pins any
318 * address_space that has radix tree nodes on the LRU.
319 *
320 * We can then safely transition to the mapping->tree_lock to
321 * pin only the address_space of the particular node we want
322 * to reclaim, take the node off-LRU, and drop the lru_lock.
323 */
324
325 node = container_of(item, struct radix_tree_node, private_list);
326 mapping = node->private_data;
327
328 /* Coming from the list, invert the lock order */
329 if (!spin_trylock(&mapping->tree_lock)) {
330 spin_unlock(lru_lock);
331 ret = LRU_RETRY;
332 goto out;
333 }
334
335 list_del_init(item);
336 spin_unlock(lru_lock);
337
338 /*
339 * The nodes should only contain one or more shadow entries,
340 * no pages, so we expect to be able to remove them all and
341 * delete and free the empty node afterwards.
342 */
343
344 BUG_ON(!node->count);
345 BUG_ON(node->count & RADIX_TREE_COUNT_MASK);
346
347 for (i = 0; i < RADIX_TREE_MAP_SIZE; i++) {
348 if (node->slots[i]) {
349 BUG_ON(!radix_tree_exceptional_entry(node->slots[i]));
350 node->slots[i] = NULL;
351 BUG_ON(node->count < (1U << RADIX_TREE_COUNT_SHIFT));
352 node->count -= 1U << RADIX_TREE_COUNT_SHIFT;
353 BUG_ON(!mapping->nrshadows);
354 mapping->nrshadows--;
355 }
356 }
357 BUG_ON(node->count);
358 inc_zone_state(page_zone(virt_to_page(node)), WORKINGSET_NODERECLAIM);
359 if (!__radix_tree_delete_node(&mapping->page_tree, node))
360 BUG();
361
362 spin_unlock(&mapping->tree_lock);
363 ret = LRU_REMOVED_RETRY;
364out:
365 local_irq_enable();
366 cond_resched();
367 local_irq_disable();
368 spin_lock(lru_lock);
369 return ret;
370}
371
372static unsigned long scan_shadow_nodes(struct shrinker *shrinker,
373 struct shrink_control *sc)
374{
375 unsigned long ret;
376
377 /* list_lru lock nests inside IRQ-safe mapping->tree_lock */
378 local_irq_disable();
379 ret = list_lru_walk_node(&workingset_shadow_nodes, sc->nid,
380 shadow_lru_isolate, NULL, &sc->nr_to_scan);
381 local_irq_enable();
382 return ret;
383}
384
385static struct shrinker workingset_shadow_shrinker = {
386 .count_objects = count_shadow_nodes,
387 .scan_objects = scan_shadow_nodes,
388 .seeks = DEFAULT_SEEKS,
389 .flags = SHRINKER_NUMA_AWARE,
390};
391
392/*
393 * Our list_lru->lock is IRQ-safe as it nests inside the IRQ-safe
394 * mapping->tree_lock.
395 */
396static struct lock_class_key shadow_nodes_key;
397
398static int __init workingset_init(void)
399{
400 int ret;
401
402 ret = list_lru_init_key(&workingset_shadow_nodes, &shadow_nodes_key);
403 if (ret)
404 goto err;
405 ret = register_shrinker(&workingset_shadow_shrinker);
406 if (ret)
407 goto err_list_lru;
408 return 0;
409err_list_lru:
410 list_lru_destroy(&workingset_shadow_nodes);
411err:
412 return ret;
413}
414module_init(workingset_init);
1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Workingset detection
4 *
5 * Copyright (C) 2013 Red Hat, Inc., Johannes Weiner
6 */
7
8#include <linux/memcontrol.h>
9#include <linux/mm_inline.h>
10#include <linux/writeback.h>
11#include <linux/shmem_fs.h>
12#include <linux/pagemap.h>
13#include <linux/atomic.h>
14#include <linux/module.h>
15#include <linux/swap.h>
16#include <linux/dax.h>
17#include <linux/fs.h>
18#include <linux/mm.h>
19
20/*
21 * Double CLOCK lists
22 *
23 * Per node, two clock lists are maintained for file pages: the
24 * inactive and the active list. Freshly faulted pages start out at
25 * the head of the inactive list and page reclaim scans pages from the
26 * tail. Pages that are accessed multiple times on the inactive list
27 * are promoted to the active list, to protect them from reclaim,
28 * whereas active pages are demoted to the inactive list when the
29 * active list grows too big.
30 *
31 * fault ------------------------+
32 * |
33 * +--------------+ | +-------------+
34 * reclaim <- | inactive | <-+-- demotion | active | <--+
35 * +--------------+ +-------------+ |
36 * | |
37 * +-------------- promotion ------------------+
38 *
39 *
40 * Access frequency and refault distance
41 *
42 * A workload is thrashing when its pages are frequently used but they
43 * are evicted from the inactive list every time before another access
44 * would have promoted them to the active list.
45 *
46 * In cases where the average access distance between thrashing pages
47 * is bigger than the size of memory there is nothing that can be
48 * done - the thrashing set could never fit into memory under any
49 * circumstance.
50 *
51 * However, the average access distance could be bigger than the
52 * inactive list, yet smaller than the size of memory. In this case,
53 * the set could fit into memory if it weren't for the currently
54 * active pages - which may be used more, hopefully less frequently:
55 *
56 * +-memory available to cache-+
57 * | |
58 * +-inactive------+-active----+
59 * a b | c d e f g h i | J K L M N |
60 * +---------------+-----------+
61 *
62 * It is prohibitively expensive to accurately track access frequency
63 * of pages. But a reasonable approximation can be made to measure
64 * thrashing on the inactive list, after which refaulting pages can be
65 * activated optimistically to compete with the existing active pages.
66 *
67 * Approximating inactive page access frequency - Observations:
68 *
69 * 1. When a page is accessed for the first time, it is added to the
70 * head of the inactive list, slides every existing inactive page
71 * towards the tail by one slot, and pushes the current tail page
72 * out of memory.
73 *
74 * 2. When a page is accessed for the second time, it is promoted to
75 * the active list, shrinking the inactive list by one slot. This
76 * also slides all inactive pages that were faulted into the cache
77 * more recently than the activated page towards the tail of the
78 * inactive list.
79 *
80 * Thus:
81 *
82 * 1. The sum of evictions and activations between any two points in
83 * time indicate the minimum number of inactive pages accessed in
84 * between.
85 *
86 * 2. Moving one inactive page N page slots towards the tail of the
87 * list requires at least N inactive page accesses.
88 *
89 * Combining these:
90 *
91 * 1. When a page is finally evicted from memory, the number of
92 * inactive pages accessed while the page was in cache is at least
93 * the number of page slots on the inactive list.
94 *
95 * 2. In addition, measuring the sum of evictions and activations (E)
96 * at the time of a page's eviction, and comparing it to another
97 * reading (R) at the time the page faults back into memory tells
98 * the minimum number of accesses while the page was not cached.
99 * This is called the refault distance.
100 *
101 * Because the first access of the page was the fault and the second
102 * access the refault, we combine the in-cache distance with the
103 * out-of-cache distance to get the complete minimum access distance
104 * of this page:
105 *
106 * NR_inactive + (R - E)
107 *
108 * And knowing the minimum access distance of a page, we can easily
109 * tell if the page would be able to stay in cache assuming all page
110 * slots in the cache were available:
111 *
112 * NR_inactive + (R - E) <= NR_inactive + NR_active
113 *
114 * which can be further simplified to
115 *
116 * (R - E) <= NR_active
117 *
118 * Put into words, the refault distance (out-of-cache) can be seen as
119 * a deficit in inactive list space (in-cache). If the inactive list
120 * had (R - E) more page slots, the page would not have been evicted
121 * in between accesses, but activated instead. And on a full system,
122 * the only thing eating into inactive list space is active pages.
123 *
124 *
125 * Refaulting inactive pages
126 *
127 * All that is known about the active list is that the pages have been
128 * accessed more than once in the past. This means that at any given
129 * time there is actually a good chance that pages on the active list
130 * are no longer in active use.
131 *
132 * So when a refault distance of (R - E) is observed and there are at
133 * least (R - E) active pages, the refaulting page is activated
134 * optimistically in the hope that (R - E) active pages are actually
135 * used less frequently than the refaulting page - or even not used at
136 * all anymore.
137 *
138 * That means if inactive cache is refaulting with a suitable refault
139 * distance, we assume the cache workingset is transitioning and put
140 * pressure on the current active list.
141 *
142 * If this is wrong and demotion kicks in, the pages which are truly
143 * used more frequently will be reactivated while the less frequently
144 * used once will be evicted from memory.
145 *
146 * But if this is right, the stale pages will be pushed out of memory
147 * and the used pages get to stay in cache.
148 *
149 * Refaulting active pages
150 *
151 * If on the other hand the refaulting pages have recently been
152 * deactivated, it means that the active list is no longer protecting
153 * actively used cache from reclaim. The cache is NOT transitioning to
154 * a different workingset; the existing workingset is thrashing in the
155 * space allocated to the page cache.
156 *
157 *
158 * Implementation
159 *
160 * For each node's LRU lists, a counter for inactive evictions and
161 * activations is maintained (node->nonresident_age).
162 *
163 * On eviction, a snapshot of this counter (along with some bits to
164 * identify the node) is stored in the now empty page cache
165 * slot of the evicted page. This is called a shadow entry.
166 *
167 * On cache misses for which there are shadow entries, an eligible
168 * refault distance will immediately activate the refaulting page.
169 */
170
171#define WORKINGSET_SHIFT 1
172#define EVICTION_SHIFT ((BITS_PER_LONG - BITS_PER_XA_VALUE) + \
173 WORKINGSET_SHIFT + NODES_SHIFT + \
174 MEM_CGROUP_ID_SHIFT)
175#define EVICTION_MASK (~0UL >> EVICTION_SHIFT)
176
177/*
178 * Eviction timestamps need to be able to cover the full range of
179 * actionable refaults. However, bits are tight in the xarray
180 * entry, and after storing the identifier for the lruvec there might
181 * not be enough left to represent every single actionable refault. In
182 * that case, we have to sacrifice granularity for distance, and group
183 * evictions into coarser buckets by shaving off lower timestamp bits.
184 */
185static unsigned int bucket_order __read_mostly;
186
187static void *pack_shadow(int memcgid, pg_data_t *pgdat, unsigned long eviction,
188 bool workingset)
189{
190 eviction &= EVICTION_MASK;
191 eviction = (eviction << MEM_CGROUP_ID_SHIFT) | memcgid;
192 eviction = (eviction << NODES_SHIFT) | pgdat->node_id;
193 eviction = (eviction << WORKINGSET_SHIFT) | workingset;
194
195 return xa_mk_value(eviction);
196}
197
198static void unpack_shadow(void *shadow, int *memcgidp, pg_data_t **pgdat,
199 unsigned long *evictionp, bool *workingsetp)
200{
201 unsigned long entry = xa_to_value(shadow);
202 int memcgid, nid;
203 bool workingset;
204
205 workingset = entry & ((1UL << WORKINGSET_SHIFT) - 1);
206 entry >>= WORKINGSET_SHIFT;
207 nid = entry & ((1UL << NODES_SHIFT) - 1);
208 entry >>= NODES_SHIFT;
209 memcgid = entry & ((1UL << MEM_CGROUP_ID_SHIFT) - 1);
210 entry >>= MEM_CGROUP_ID_SHIFT;
211
212 *memcgidp = memcgid;
213 *pgdat = NODE_DATA(nid);
214 *evictionp = entry;
215 *workingsetp = workingset;
216}
217
218#ifdef CONFIG_LRU_GEN
219
220static void *lru_gen_eviction(struct folio *folio)
221{
222 int hist;
223 unsigned long token;
224 unsigned long min_seq;
225 struct lruvec *lruvec;
226 struct lru_gen_struct *lrugen;
227 int type = folio_is_file_lru(folio);
228 int delta = folio_nr_pages(folio);
229 int refs = folio_lru_refs(folio);
230 int tier = lru_tier_from_refs(refs);
231 struct mem_cgroup *memcg = folio_memcg(folio);
232 struct pglist_data *pgdat = folio_pgdat(folio);
233
234 BUILD_BUG_ON(LRU_GEN_WIDTH + LRU_REFS_WIDTH > BITS_PER_LONG - EVICTION_SHIFT);
235
236 lruvec = mem_cgroup_lruvec(memcg, pgdat);
237 lrugen = &lruvec->lrugen;
238 min_seq = READ_ONCE(lrugen->min_seq[type]);
239 token = (min_seq << LRU_REFS_WIDTH) | max(refs - 1, 0);
240
241 hist = lru_hist_from_seq(min_seq);
242 atomic_long_add(delta, &lrugen->evicted[hist][type][tier]);
243
244 return pack_shadow(mem_cgroup_id(memcg), pgdat, token, refs);
245}
246
247static void lru_gen_refault(struct folio *folio, void *shadow)
248{
249 int hist, tier, refs;
250 int memcg_id;
251 bool workingset;
252 unsigned long token;
253 unsigned long min_seq;
254 struct lruvec *lruvec;
255 struct lru_gen_struct *lrugen;
256 struct mem_cgroup *memcg;
257 struct pglist_data *pgdat;
258 int type = folio_is_file_lru(folio);
259 int delta = folio_nr_pages(folio);
260
261 unpack_shadow(shadow, &memcg_id, &pgdat, &token, &workingset);
262
263 if (pgdat != folio_pgdat(folio))
264 return;
265
266 rcu_read_lock();
267
268 memcg = folio_memcg_rcu(folio);
269 if (memcg_id != mem_cgroup_id(memcg))
270 goto unlock;
271
272 lruvec = mem_cgroup_lruvec(memcg, pgdat);
273 lrugen = &lruvec->lrugen;
274
275 min_seq = READ_ONCE(lrugen->min_seq[type]);
276 if ((token >> LRU_REFS_WIDTH) != (min_seq & (EVICTION_MASK >> LRU_REFS_WIDTH)))
277 goto unlock;
278
279 hist = lru_hist_from_seq(min_seq);
280 /* see the comment in folio_lru_refs() */
281 refs = (token & (BIT(LRU_REFS_WIDTH) - 1)) + workingset;
282 tier = lru_tier_from_refs(refs);
283
284 atomic_long_add(delta, &lrugen->refaulted[hist][type][tier]);
285 mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + type, delta);
286
287 /*
288 * Count the following two cases as stalls:
289 * 1. For pages accessed through page tables, hotter pages pushed out
290 * hot pages which refaulted immediately.
291 * 2. For pages accessed multiple times through file descriptors,
292 * numbers of accesses might have been out of the range.
293 */
294 if (lru_gen_in_fault() || refs == BIT(LRU_REFS_WIDTH)) {
295 folio_set_workingset(folio);
296 mod_lruvec_state(lruvec, WORKINGSET_RESTORE_BASE + type, delta);
297 }
298unlock:
299 rcu_read_unlock();
300}
301
302#else /* !CONFIG_LRU_GEN */
303
304static void *lru_gen_eviction(struct folio *folio)
305{
306 return NULL;
307}
308
309static void lru_gen_refault(struct folio *folio, void *shadow)
310{
311}
312
313#endif /* CONFIG_LRU_GEN */
314
315/**
316 * workingset_age_nonresident - age non-resident entries as LRU ages
317 * @lruvec: the lruvec that was aged
318 * @nr_pages: the number of pages to count
319 *
320 * As in-memory pages are aged, non-resident pages need to be aged as
321 * well, in order for the refault distances later on to be comparable
322 * to the in-memory dimensions. This function allows reclaim and LRU
323 * operations to drive the non-resident aging along in parallel.
324 */
325void workingset_age_nonresident(struct lruvec *lruvec, unsigned long nr_pages)
326{
327 /*
328 * Reclaiming a cgroup means reclaiming all its children in a
329 * round-robin fashion. That means that each cgroup has an LRU
330 * order that is composed of the LRU orders of its child
331 * cgroups; and every page has an LRU position not just in the
332 * cgroup that owns it, but in all of that group's ancestors.
333 *
334 * So when the physical inactive list of a leaf cgroup ages,
335 * the virtual inactive lists of all its parents, including
336 * the root cgroup's, age as well.
337 */
338 do {
339 atomic_long_add(nr_pages, &lruvec->nonresident_age);
340 } while ((lruvec = parent_lruvec(lruvec)));
341}
342
343/**
344 * workingset_eviction - note the eviction of a folio from memory
345 * @target_memcg: the cgroup that is causing the reclaim
346 * @folio: the folio being evicted
347 *
348 * Return: a shadow entry to be stored in @folio->mapping->i_pages in place
349 * of the evicted @folio so that a later refault can be detected.
350 */
351void *workingset_eviction(struct folio *folio, struct mem_cgroup *target_memcg)
352{
353 struct pglist_data *pgdat = folio_pgdat(folio);
354 unsigned long eviction;
355 struct lruvec *lruvec;
356 int memcgid;
357
358 /* Folio is fully exclusive and pins folio's memory cgroup pointer */
359 VM_BUG_ON_FOLIO(folio_test_lru(folio), folio);
360 VM_BUG_ON_FOLIO(folio_ref_count(folio), folio);
361 VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
362
363 if (lru_gen_enabled())
364 return lru_gen_eviction(folio);
365
366 lruvec = mem_cgroup_lruvec(target_memcg, pgdat);
367 /* XXX: target_memcg can be NULL, go through lruvec */
368 memcgid = mem_cgroup_id(lruvec_memcg(lruvec));
369 eviction = atomic_long_read(&lruvec->nonresident_age);
370 eviction >>= bucket_order;
371 workingset_age_nonresident(lruvec, folio_nr_pages(folio));
372 return pack_shadow(memcgid, pgdat, eviction,
373 folio_test_workingset(folio));
374}
375
376/**
377 * workingset_refault - Evaluate the refault of a previously evicted folio.
378 * @folio: The freshly allocated replacement folio.
379 * @shadow: Shadow entry of the evicted folio.
380 *
381 * Calculates and evaluates the refault distance of the previously
382 * evicted folio in the context of the node and the memcg whose memory
383 * pressure caused the eviction.
384 */
385void workingset_refault(struct folio *folio, void *shadow)
386{
387 bool file = folio_is_file_lru(folio);
388 struct mem_cgroup *eviction_memcg;
389 struct lruvec *eviction_lruvec;
390 unsigned long refault_distance;
391 unsigned long workingset_size;
392 struct pglist_data *pgdat;
393 struct mem_cgroup *memcg;
394 unsigned long eviction;
395 struct lruvec *lruvec;
396 unsigned long refault;
397 bool workingset;
398 int memcgid;
399 long nr;
400
401 if (lru_gen_enabled()) {
402 lru_gen_refault(folio, shadow);
403 return;
404 }
405
406 unpack_shadow(shadow, &memcgid, &pgdat, &eviction, &workingset);
407 eviction <<= bucket_order;
408
409 rcu_read_lock();
410 /*
411 * Look up the memcg associated with the stored ID. It might
412 * have been deleted since the folio's eviction.
413 *
414 * Note that in rare events the ID could have been recycled
415 * for a new cgroup that refaults a shared folio. This is
416 * impossible to tell from the available data. However, this
417 * should be a rare and limited disturbance, and activations
418 * are always speculative anyway. Ultimately, it's the aging
419 * algorithm's job to shake out the minimum access frequency
420 * for the active cache.
421 *
422 * XXX: On !CONFIG_MEMCG, this will always return NULL; it
423 * would be better if the root_mem_cgroup existed in all
424 * configurations instead.
425 */
426 eviction_memcg = mem_cgroup_from_id(memcgid);
427 if (!mem_cgroup_disabled() && !eviction_memcg)
428 goto out;
429 eviction_lruvec = mem_cgroup_lruvec(eviction_memcg, pgdat);
430 refault = atomic_long_read(&eviction_lruvec->nonresident_age);
431
432 /*
433 * Calculate the refault distance
434 *
435 * The unsigned subtraction here gives an accurate distance
436 * across nonresident_age overflows in most cases. There is a
437 * special case: usually, shadow entries have a short lifetime
438 * and are either refaulted or reclaimed along with the inode
439 * before they get too old. But it is not impossible for the
440 * nonresident_age to lap a shadow entry in the field, which
441 * can then result in a false small refault distance, leading
442 * to a false activation should this old entry actually
443 * refault again. However, earlier kernels used to deactivate
444 * unconditionally with *every* reclaim invocation for the
445 * longest time, so the occasional inappropriate activation
446 * leading to pressure on the active list is not a problem.
447 */
448 refault_distance = (refault - eviction) & EVICTION_MASK;
449
450 /*
451 * The activation decision for this folio is made at the level
452 * where the eviction occurred, as that is where the LRU order
453 * during folio reclaim is being determined.
454 *
455 * However, the cgroup that will own the folio is the one that
456 * is actually experiencing the refault event.
457 */
458 nr = folio_nr_pages(folio);
459 memcg = folio_memcg(folio);
460 lruvec = mem_cgroup_lruvec(memcg, pgdat);
461
462 mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + file, nr);
463
464 mem_cgroup_flush_stats_delayed();
465 /*
466 * Compare the distance to the existing workingset size. We
467 * don't activate pages that couldn't stay resident even if
468 * all the memory was available to the workingset. Whether
469 * workingset competition needs to consider anon or not depends
470 * on having swap.
471 */
472 workingset_size = lruvec_page_state(eviction_lruvec, NR_ACTIVE_FILE);
473 if (!file) {
474 workingset_size += lruvec_page_state(eviction_lruvec,
475 NR_INACTIVE_FILE);
476 }
477 if (mem_cgroup_get_nr_swap_pages(memcg) > 0) {
478 workingset_size += lruvec_page_state(eviction_lruvec,
479 NR_ACTIVE_ANON);
480 if (file) {
481 workingset_size += lruvec_page_state(eviction_lruvec,
482 NR_INACTIVE_ANON);
483 }
484 }
485 if (refault_distance > workingset_size)
486 goto out;
487
488 folio_set_active(folio);
489 workingset_age_nonresident(lruvec, nr);
490 mod_lruvec_state(lruvec, WORKINGSET_ACTIVATE_BASE + file, nr);
491
492 /* Folio was active prior to eviction */
493 if (workingset) {
494 folio_set_workingset(folio);
495 /*
496 * XXX: Move to folio_add_lru() when it supports new vs
497 * putback
498 */
499 lru_note_cost_refault(folio);
500 mod_lruvec_state(lruvec, WORKINGSET_RESTORE_BASE + file, nr);
501 }
502out:
503 rcu_read_unlock();
504}
505
506/**
507 * workingset_activation - note a page activation
508 * @folio: Folio that is being activated.
509 */
510void workingset_activation(struct folio *folio)
511{
512 struct mem_cgroup *memcg;
513
514 rcu_read_lock();
515 /*
516 * Filter non-memcg pages here, e.g. unmap can call
517 * mark_page_accessed() on VDSO pages.
518 *
519 * XXX: See workingset_refault() - this should return
520 * root_mem_cgroup even for !CONFIG_MEMCG.
521 */
522 memcg = folio_memcg_rcu(folio);
523 if (!mem_cgroup_disabled() && !memcg)
524 goto out;
525 workingset_age_nonresident(folio_lruvec(folio), folio_nr_pages(folio));
526out:
527 rcu_read_unlock();
528}
529
530/*
531 * Shadow entries reflect the share of the working set that does not
532 * fit into memory, so their number depends on the access pattern of
533 * the workload. In most cases, they will refault or get reclaimed
534 * along with the inode, but a (malicious) workload that streams
535 * through files with a total size several times that of available
536 * memory, while preventing the inodes from being reclaimed, can
537 * create excessive amounts of shadow nodes. To keep a lid on this,
538 * track shadow nodes and reclaim them when they grow way past the
539 * point where they would still be useful.
540 */
541
542struct list_lru shadow_nodes;
543
544void workingset_update_node(struct xa_node *node)
545{
546 struct address_space *mapping;
547
548 /*
549 * Track non-empty nodes that contain only shadow entries;
550 * unlink those that contain pages or are being freed.
551 *
552 * Avoid acquiring the list_lru lock when the nodes are
553 * already where they should be. The list_empty() test is safe
554 * as node->private_list is protected by the i_pages lock.
555 */
556 mapping = container_of(node->array, struct address_space, i_pages);
557 lockdep_assert_held(&mapping->i_pages.xa_lock);
558
559 if (node->count && node->count == node->nr_values) {
560 if (list_empty(&node->private_list)) {
561 list_lru_add(&shadow_nodes, &node->private_list);
562 __inc_lruvec_kmem_state(node, WORKINGSET_NODES);
563 }
564 } else {
565 if (!list_empty(&node->private_list)) {
566 list_lru_del(&shadow_nodes, &node->private_list);
567 __dec_lruvec_kmem_state(node, WORKINGSET_NODES);
568 }
569 }
570}
571
572static unsigned long count_shadow_nodes(struct shrinker *shrinker,
573 struct shrink_control *sc)
574{
575 unsigned long max_nodes;
576 unsigned long nodes;
577 unsigned long pages;
578
579 nodes = list_lru_shrink_count(&shadow_nodes, sc);
580 if (!nodes)
581 return SHRINK_EMPTY;
582
583 /*
584 * Approximate a reasonable limit for the nodes
585 * containing shadow entries. We don't need to keep more
586 * shadow entries than possible pages on the active list,
587 * since refault distances bigger than that are dismissed.
588 *
589 * The size of the active list converges toward 100% of
590 * overall page cache as memory grows, with only a tiny
591 * inactive list. Assume the total cache size for that.
592 *
593 * Nodes might be sparsely populated, with only one shadow
594 * entry in the extreme case. Obviously, we cannot keep one
595 * node for every eligible shadow entry, so compromise on a
596 * worst-case density of 1/8th. Below that, not all eligible
597 * refaults can be detected anymore.
598 *
599 * On 64-bit with 7 xa_nodes per page and 64 slots
600 * each, this will reclaim shadow entries when they consume
601 * ~1.8% of available memory:
602 *
603 * PAGE_SIZE / xa_nodes / node_entries * 8 / PAGE_SIZE
604 */
605#ifdef CONFIG_MEMCG
606 if (sc->memcg) {
607 struct lruvec *lruvec;
608 int i;
609
610 lruvec = mem_cgroup_lruvec(sc->memcg, NODE_DATA(sc->nid));
611 for (pages = 0, i = 0; i < NR_LRU_LISTS; i++)
612 pages += lruvec_page_state_local(lruvec,
613 NR_LRU_BASE + i);
614 pages += lruvec_page_state_local(
615 lruvec, NR_SLAB_RECLAIMABLE_B) >> PAGE_SHIFT;
616 pages += lruvec_page_state_local(
617 lruvec, NR_SLAB_UNRECLAIMABLE_B) >> PAGE_SHIFT;
618 } else
619#endif
620 pages = node_present_pages(sc->nid);
621
622 max_nodes = pages >> (XA_CHUNK_SHIFT - 3);
623
624 if (nodes <= max_nodes)
625 return 0;
626 return nodes - max_nodes;
627}
628
629static enum lru_status shadow_lru_isolate(struct list_head *item,
630 struct list_lru_one *lru,
631 spinlock_t *lru_lock,
632 void *arg) __must_hold(lru_lock)
633{
634 struct xa_node *node = container_of(item, struct xa_node, private_list);
635 struct address_space *mapping;
636 int ret;
637
638 /*
639 * Page cache insertions and deletions synchronously maintain
640 * the shadow node LRU under the i_pages lock and the
641 * lru_lock. Because the page cache tree is emptied before
642 * the inode can be destroyed, holding the lru_lock pins any
643 * address_space that has nodes on the LRU.
644 *
645 * We can then safely transition to the i_pages lock to
646 * pin only the address_space of the particular node we want
647 * to reclaim, take the node off-LRU, and drop the lru_lock.
648 */
649
650 mapping = container_of(node->array, struct address_space, i_pages);
651
652 /* Coming from the list, invert the lock order */
653 if (!xa_trylock(&mapping->i_pages)) {
654 spin_unlock_irq(lru_lock);
655 ret = LRU_RETRY;
656 goto out;
657 }
658
659 if (!spin_trylock(&mapping->host->i_lock)) {
660 xa_unlock(&mapping->i_pages);
661 spin_unlock_irq(lru_lock);
662 ret = LRU_RETRY;
663 goto out;
664 }
665
666 list_lru_isolate(lru, item);
667 __dec_lruvec_kmem_state(node, WORKINGSET_NODES);
668
669 spin_unlock(lru_lock);
670
671 /*
672 * The nodes should only contain one or more shadow entries,
673 * no pages, so we expect to be able to remove them all and
674 * delete and free the empty node afterwards.
675 */
676 if (WARN_ON_ONCE(!node->nr_values))
677 goto out_invalid;
678 if (WARN_ON_ONCE(node->count != node->nr_values))
679 goto out_invalid;
680 xa_delete_node(node, workingset_update_node);
681 __inc_lruvec_kmem_state(node, WORKINGSET_NODERECLAIM);
682
683out_invalid:
684 xa_unlock_irq(&mapping->i_pages);
685 if (mapping_shrinkable(mapping))
686 inode_add_lru(mapping->host);
687 spin_unlock(&mapping->host->i_lock);
688 ret = LRU_REMOVED_RETRY;
689out:
690 cond_resched();
691 spin_lock_irq(lru_lock);
692 return ret;
693}
694
695static unsigned long scan_shadow_nodes(struct shrinker *shrinker,
696 struct shrink_control *sc)
697{
698 /* list_lru lock nests inside the IRQ-safe i_pages lock */
699 return list_lru_shrink_walk_irq(&shadow_nodes, sc, shadow_lru_isolate,
700 NULL);
701}
702
703static struct shrinker workingset_shadow_shrinker = {
704 .count_objects = count_shadow_nodes,
705 .scan_objects = scan_shadow_nodes,
706 .seeks = 0, /* ->count reports only fully expendable nodes */
707 .flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE,
708};
709
710/*
711 * Our list_lru->lock is IRQ-safe as it nests inside the IRQ-safe
712 * i_pages lock.
713 */
714static struct lock_class_key shadow_nodes_key;
715
716static int __init workingset_init(void)
717{
718 unsigned int timestamp_bits;
719 unsigned int max_order;
720 int ret;
721
722 BUILD_BUG_ON(BITS_PER_LONG < EVICTION_SHIFT);
723 /*
724 * Calculate the eviction bucket size to cover the longest
725 * actionable refault distance, which is currently half of
726 * memory (totalram_pages/2). However, memory hotplug may add
727 * some more pages at runtime, so keep working with up to
728 * double the initial memory by using totalram_pages as-is.
729 */
730 timestamp_bits = BITS_PER_LONG - EVICTION_SHIFT;
731 max_order = fls_long(totalram_pages() - 1);
732 if (max_order > timestamp_bits)
733 bucket_order = max_order - timestamp_bits;
734 pr_info("workingset: timestamp_bits=%d max_order=%d bucket_order=%u\n",
735 timestamp_bits, max_order, bucket_order);
736
737 ret = prealloc_shrinker(&workingset_shadow_shrinker, "mm-shadow");
738 if (ret)
739 goto err;
740 ret = __list_lru_init(&shadow_nodes, true, &shadow_nodes_key,
741 &workingset_shadow_shrinker);
742 if (ret)
743 goto err_list_lru;
744 register_shrinker_prepared(&workingset_shadow_shrinker);
745 return 0;
746err_list_lru:
747 free_prealloced_shrinker(&workingset_shadow_shrinker);
748err:
749 return ret;
750}
751module_init(workingset_init);