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