Line data Source code
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 : */
185 : static unsigned int bucket_order __read_mostly;
186 :
187 0 : static void *pack_shadow(int memcgid, pg_data_t *pgdat, unsigned long eviction,
188 : bool workingset)
189 : {
190 0 : eviction &= EVICTION_MASK;
191 0 : eviction = (eviction << MEM_CGROUP_ID_SHIFT) | memcgid;
192 0 : eviction = (eviction << NODES_SHIFT) | pgdat->node_id;
193 0 : eviction = (eviction << WORKINGSET_SHIFT) | workingset;
194 :
195 0 : return xa_mk_value(eviction);
196 : }
197 :
198 : static void unpack_shadow(void *shadow, int *memcgidp, pg_data_t **pgdat,
199 : unsigned long *evictionp, bool *workingsetp)
200 : {
201 0 : unsigned long entry = xa_to_value(shadow);
202 : int memcgid, nid;
203 : bool workingset;
204 :
205 0 : workingset = entry & ((1UL << WORKINGSET_SHIFT) - 1);
206 0 : entry >>= WORKINGSET_SHIFT;
207 0 : nid = entry & ((1UL << NODES_SHIFT) - 1);
208 0 : entry >>= NODES_SHIFT;
209 0 : memcgid = entry & ((1UL << MEM_CGROUP_ID_SHIFT) - 1);
210 0 : entry >>= MEM_CGROUP_ID_SHIFT;
211 :
212 0 : *memcgidp = memcgid;
213 0 : *pgdat = NODE_DATA(nid);
214 0 : *evictionp = entry;
215 0 : *workingsetp = workingset;
216 : }
217 :
218 : #ifdef CONFIG_LRU_GEN
219 :
220 : static 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_folio *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 :
247 : static 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_folio *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 : }
298 : unlock:
299 : rcu_read_unlock();
300 : }
301 :
302 : #else /* !CONFIG_LRU_GEN */
303 :
304 : static void *lru_gen_eviction(struct folio *folio)
305 : {
306 : return NULL;
307 : }
308 :
309 : static 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 : */
325 0 : void 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 0 : atomic_long_add(nr_pages, &lruvec->nonresident_age);
340 0 : } while ((lruvec = parent_lruvec(lruvec)));
341 0 : }
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 : */
351 0 : void *workingset_eviction(struct folio *folio, struct mem_cgroup *target_memcg)
352 : {
353 0 : 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 0 : lruvec = mem_cgroup_lruvec(target_memcg, pgdat);
367 : /* XXX: target_memcg can be NULL, go through lruvec */
368 0 : memcgid = mem_cgroup_id(lruvec_memcg(lruvec));
369 0 : eviction = atomic_long_read(&lruvec->nonresident_age);
370 0 : eviction >>= bucket_order;
371 0 : workingset_age_nonresident(lruvec, folio_nr_pages(folio));
372 0 : return pack_shadow(memcgid, pgdat, eviction,
373 0 : 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 : */
385 0 : void workingset_refault(struct folio *folio, void *shadow)
386 : {
387 0 : 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 0 : unpack_shadow(shadow, &memcgid, &pgdat, &eviction, &workingset);
407 0 : 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 0 : eviction_memcg = mem_cgroup_from_id(memcgid);
427 : if (!mem_cgroup_disabled() && !eviction_memcg)
428 : goto out;
429 0 : eviction_lruvec = mem_cgroup_lruvec(eviction_memcg, pgdat);
430 0 : 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 0 : 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 0 : nr = folio_nr_pages(folio);
459 0 : memcg = folio_memcg(folio);
460 0 : pgdat = folio_pgdat(folio);
461 0 : lruvec = mem_cgroup_lruvec(memcg, pgdat);
462 :
463 0 : mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + file, nr);
464 :
465 : mem_cgroup_flush_stats_delayed();
466 : /*
467 : * Compare the distance to the existing workingset size. We
468 : * don't activate pages that couldn't stay resident even if
469 : * all the memory was available to the workingset. Whether
470 : * workingset competition needs to consider anon or not depends
471 : * on having swap.
472 : */
473 0 : workingset_size = lruvec_page_state(eviction_lruvec, NR_ACTIVE_FILE);
474 0 : if (!file) {
475 0 : workingset_size += lruvec_page_state(eviction_lruvec,
476 : NR_INACTIVE_FILE);
477 : }
478 0 : if (mem_cgroup_get_nr_swap_pages(eviction_memcg) > 0) {
479 0 : workingset_size += lruvec_page_state(eviction_lruvec,
480 : NR_ACTIVE_ANON);
481 0 : if (file) {
482 0 : workingset_size += lruvec_page_state(eviction_lruvec,
483 : NR_INACTIVE_ANON);
484 : }
485 : }
486 0 : if (refault_distance > workingset_size)
487 : goto out;
488 :
489 0 : folio_set_active(folio);
490 0 : workingset_age_nonresident(lruvec, nr);
491 0 : mod_lruvec_state(lruvec, WORKINGSET_ACTIVATE_BASE + file, nr);
492 :
493 : /* Folio was active prior to eviction */
494 0 : if (workingset) {
495 0 : folio_set_workingset(folio);
496 : /*
497 : * XXX: Move to folio_add_lru() when it supports new vs
498 : * putback
499 : */
500 0 : lru_note_cost_refault(folio);
501 0 : mod_lruvec_state(lruvec, WORKINGSET_RESTORE_BASE + file, nr);
502 : }
503 : out:
504 : rcu_read_unlock();
505 : }
506 :
507 : /**
508 : * workingset_activation - note a page activation
509 : * @folio: Folio that is being activated.
510 : */
511 0 : void workingset_activation(struct folio *folio)
512 : {
513 : struct mem_cgroup *memcg;
514 :
515 : rcu_read_lock();
516 : /*
517 : * Filter non-memcg pages here, e.g. unmap can call
518 : * mark_page_accessed() on VDSO pages.
519 : *
520 : * XXX: See workingset_refault() - this should return
521 : * root_mem_cgroup even for !CONFIG_MEMCG.
522 : */
523 0 : memcg = folio_memcg_rcu(folio);
524 : if (!mem_cgroup_disabled() && !memcg)
525 : goto out;
526 0 : workingset_age_nonresident(folio_lruvec(folio), folio_nr_pages(folio));
527 : out:
528 : rcu_read_unlock();
529 0 : }
530 :
531 : /*
532 : * Shadow entries reflect the share of the working set that does not
533 : * fit into memory, so their number depends on the access pattern of
534 : * the workload. In most cases, they will refault or get reclaimed
535 : * along with the inode, but a (malicious) workload that streams
536 : * through files with a total size several times that of available
537 : * memory, while preventing the inodes from being reclaimed, can
538 : * create excessive amounts of shadow nodes. To keep a lid on this,
539 : * track shadow nodes and reclaim them when they grow way past the
540 : * point where they would still be useful.
541 : */
542 :
543 : struct list_lru shadow_nodes;
544 :
545 0 : void workingset_update_node(struct xa_node *node)
546 : {
547 : struct address_space *mapping;
548 :
549 : /*
550 : * Track non-empty nodes that contain only shadow entries;
551 : * unlink those that contain pages or are being freed.
552 : *
553 : * Avoid acquiring the list_lru lock when the nodes are
554 : * already where they should be. The list_empty() test is safe
555 : * as node->private_list is protected by the i_pages lock.
556 : */
557 0 : mapping = container_of(node->array, struct address_space, i_pages);
558 : lockdep_assert_held(&mapping->i_pages.xa_lock);
559 :
560 0 : if (node->count && node->count == node->nr_values) {
561 0 : if (list_empty(&node->private_list)) {
562 0 : list_lru_add(&shadow_nodes, &node->private_list);
563 : __inc_lruvec_kmem_state(node, WORKINGSET_NODES);
564 : }
565 : } else {
566 0 : if (!list_empty(&node->private_list)) {
567 0 : list_lru_del(&shadow_nodes, &node->private_list);
568 : __dec_lruvec_kmem_state(node, WORKINGSET_NODES);
569 : }
570 : }
571 0 : }
572 :
573 0 : static unsigned long count_shadow_nodes(struct shrinker *shrinker,
574 : struct shrink_control *sc)
575 : {
576 : unsigned long max_nodes;
577 : unsigned long nodes;
578 : unsigned long pages;
579 :
580 0 : nodes = list_lru_shrink_count(&shadow_nodes, sc);
581 0 : if (!nodes)
582 : return SHRINK_EMPTY;
583 :
584 : /*
585 : * Approximate a reasonable limit for the nodes
586 : * containing shadow entries. We don't need to keep more
587 : * shadow entries than possible pages on the active list,
588 : * since refault distances bigger than that are dismissed.
589 : *
590 : * The size of the active list converges toward 100% of
591 : * overall page cache as memory grows, with only a tiny
592 : * inactive list. Assume the total cache size for that.
593 : *
594 : * Nodes might be sparsely populated, with only one shadow
595 : * entry in the extreme case. Obviously, we cannot keep one
596 : * node for every eligible shadow entry, so compromise on a
597 : * worst-case density of 1/8th. Below that, not all eligible
598 : * refaults can be detected anymore.
599 : *
600 : * On 64-bit with 7 xa_nodes per page and 64 slots
601 : * each, this will reclaim shadow entries when they consume
602 : * ~1.8% of available memory:
603 : *
604 : * PAGE_SIZE / xa_nodes / node_entries * 8 / PAGE_SIZE
605 : */
606 : #ifdef CONFIG_MEMCG
607 : if (sc->memcg) {
608 : struct lruvec *lruvec;
609 : int i;
610 :
611 : lruvec = mem_cgroup_lruvec(sc->memcg, NODE_DATA(sc->nid));
612 : for (pages = 0, i = 0; i < NR_LRU_LISTS; i++)
613 : pages += lruvec_page_state_local(lruvec,
614 : NR_LRU_BASE + i);
615 : pages += lruvec_page_state_local(
616 : lruvec, NR_SLAB_RECLAIMABLE_B) >> PAGE_SHIFT;
617 : pages += lruvec_page_state_local(
618 : lruvec, NR_SLAB_UNRECLAIMABLE_B) >> PAGE_SHIFT;
619 : } else
620 : #endif
621 0 : pages = node_present_pages(sc->nid);
622 :
623 0 : max_nodes = pages >> (XA_CHUNK_SHIFT - 3);
624 :
625 0 : if (nodes <= max_nodes)
626 : return 0;
627 0 : return nodes - max_nodes;
628 : }
629 :
630 0 : static enum lru_status shadow_lru_isolate(struct list_head *item,
631 : struct list_lru_one *lru,
632 : spinlock_t *lru_lock,
633 : void *arg) __must_hold(lru_lock)
634 : {
635 0 : struct xa_node *node = container_of(item, struct xa_node, private_list);
636 : struct address_space *mapping;
637 : int ret;
638 :
639 : /*
640 : * Page cache insertions and deletions synchronously maintain
641 : * the shadow node LRU under the i_pages lock and the
642 : * lru_lock. Because the page cache tree is emptied before
643 : * the inode can be destroyed, holding the lru_lock pins any
644 : * address_space that has nodes on the LRU.
645 : *
646 : * We can then safely transition to the i_pages lock to
647 : * pin only the address_space of the particular node we want
648 : * to reclaim, take the node off-LRU, and drop the lru_lock.
649 : */
650 :
651 0 : mapping = container_of(node->array, struct address_space, i_pages);
652 :
653 : /* Coming from the list, invert the lock order */
654 0 : if (!xa_trylock(&mapping->i_pages)) {
655 : spin_unlock_irq(lru_lock);
656 : ret = LRU_RETRY;
657 : goto out;
658 : }
659 :
660 : /* For page cache we need to hold i_lock */
661 0 : if (mapping->host != NULL) {
662 0 : if (!spin_trylock(&mapping->host->i_lock)) {
663 : xa_unlock(&mapping->i_pages);
664 : spin_unlock_irq(lru_lock);
665 : ret = LRU_RETRY;
666 : goto out;
667 : }
668 : }
669 :
670 0 : list_lru_isolate(lru, item);
671 0 : __dec_lruvec_kmem_state(node, WORKINGSET_NODES);
672 :
673 0 : spin_unlock(lru_lock);
674 :
675 : /*
676 : * The nodes should only contain one or more shadow entries,
677 : * no pages, so we expect to be able to remove them all and
678 : * delete and free the empty node afterwards.
679 : */
680 0 : if (WARN_ON_ONCE(!node->nr_values))
681 : goto out_invalid;
682 0 : if (WARN_ON_ONCE(node->count != node->nr_values))
683 : goto out_invalid;
684 0 : xa_delete_node(node, workingset_update_node);
685 : __inc_lruvec_kmem_state(node, WORKINGSET_NODERECLAIM);
686 :
687 : out_invalid:
688 0 : xa_unlock_irq(&mapping->i_pages);
689 0 : if (mapping->host != NULL) {
690 0 : if (mapping_shrinkable(mapping))
691 0 : inode_add_lru(mapping->host);
692 0 : spin_unlock(&mapping->host->i_lock);
693 : }
694 0 : ret = LRU_REMOVED_RETRY;
695 : out:
696 0 : cond_resched();
697 0 : spin_lock_irq(lru_lock);
698 0 : return ret;
699 : }
700 :
701 0 : static unsigned long scan_shadow_nodes(struct shrinker *shrinker,
702 : struct shrink_control *sc)
703 : {
704 : /* list_lru lock nests inside the IRQ-safe i_pages lock */
705 0 : return list_lru_shrink_walk_irq(&shadow_nodes, sc, shadow_lru_isolate,
706 : NULL);
707 : }
708 :
709 : static struct shrinker workingset_shadow_shrinker = {
710 : .count_objects = count_shadow_nodes,
711 : .scan_objects = scan_shadow_nodes,
712 : .seeks = 0, /* ->count reports only fully expendable nodes */
713 : .flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE,
714 : };
715 :
716 : /*
717 : * Our list_lru->lock is IRQ-safe as it nests inside the IRQ-safe
718 : * i_pages lock.
719 : */
720 : static struct lock_class_key shadow_nodes_key;
721 :
722 1 : static int __init workingset_init(void)
723 : {
724 : unsigned int timestamp_bits;
725 : unsigned int max_order;
726 : int ret;
727 :
728 : BUILD_BUG_ON(BITS_PER_LONG < EVICTION_SHIFT);
729 : /*
730 : * Calculate the eviction bucket size to cover the longest
731 : * actionable refault distance, which is currently half of
732 : * memory (totalram_pages/2). However, memory hotplug may add
733 : * some more pages at runtime, so keep working with up to
734 : * double the initial memory by using totalram_pages as-is.
735 : */
736 1 : timestamp_bits = BITS_PER_LONG - EVICTION_SHIFT;
737 2 : max_order = fls_long(totalram_pages() - 1);
738 1 : if (max_order > timestamp_bits)
739 0 : bucket_order = max_order - timestamp_bits;
740 1 : pr_info("workingset: timestamp_bits=%d max_order=%d bucket_order=%u\n",
741 : timestamp_bits, max_order, bucket_order);
742 :
743 1 : ret = prealloc_shrinker(&workingset_shadow_shrinker, "mm-shadow");
744 1 : if (ret)
745 : goto err;
746 1 : ret = __list_lru_init(&shadow_nodes, true, &shadow_nodes_key,
747 : &workingset_shadow_shrinker);
748 1 : if (ret)
749 : goto err_list_lru;
750 1 : register_shrinker_prepared(&workingset_shadow_shrinker);
751 1 : return 0;
752 : err_list_lru:
753 0 : free_prealloced_shrinker(&workingset_shadow_shrinker);
754 : err:
755 : return ret;
756 : }
757 : module_init(workingset_init);
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