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 : * If we have swap we should consider about NR_inactive_anon and
115 : * NR_active_anon, so for page cache and anonymous respectively:
116 : *
117 : * NR_inactive_file + (R - E) <= NR_inactive_file + NR_active_file
118 : * + NR_inactive_anon + NR_active_anon
119 : *
120 : * NR_inactive_anon + (R - E) <= NR_inactive_anon + NR_active_anon
121 : * + NR_inactive_file + NR_active_file
122 : *
123 : * Which can be further simplified to:
124 : *
125 : * (R - E) <= NR_active_file + NR_inactive_anon + NR_active_anon
126 : *
127 : * (R - E) <= NR_active_anon + NR_inactive_file + NR_active_file
128 : *
129 : * Put into words, the refault distance (out-of-cache) can be seen as
130 : * a deficit in inactive list space (in-cache). If the inactive list
131 : * had (R - E) more page slots, the page would not have been evicted
132 : * in between accesses, but activated instead. And on a full system,
133 : * the only thing eating into inactive list space is active pages.
134 : *
135 : *
136 : * Refaulting inactive pages
137 : *
138 : * All that is known about the active list is that the pages have been
139 : * accessed more than once in the past. This means that at any given
140 : * time there is actually a good chance that pages on the active list
141 : * are no longer in active use.
142 : *
143 : * So when a refault distance of (R - E) is observed and there are at
144 : * least (R - E) pages in the userspace workingset, the refaulting page
145 : * is activated optimistically in the hope that (R - E) pages are actually
146 : * used less frequently than the refaulting page - or even not used at
147 : * all anymore.
148 : *
149 : * That means if inactive cache is refaulting with a suitable refault
150 : * distance, we assume the cache workingset is transitioning and put
151 : * pressure on the current workingset.
152 : *
153 : * If this is wrong and demotion kicks in, the pages which are truly
154 : * used more frequently will be reactivated while the less frequently
155 : * used once will be evicted from memory.
156 : *
157 : * But if this is right, the stale pages will be pushed out of memory
158 : * and the used pages get to stay in cache.
159 : *
160 : * Refaulting active pages
161 : *
162 : * If on the other hand the refaulting pages have recently been
163 : * deactivated, it means that the active list is no longer protecting
164 : * actively used cache from reclaim. The cache is NOT transitioning to
165 : * a different workingset; the existing workingset is thrashing in the
166 : * space allocated to the page cache.
167 : *
168 : *
169 : * Implementation
170 : *
171 : * For each node's LRU lists, a counter for inactive evictions and
172 : * activations is maintained (node->nonresident_age).
173 : *
174 : * On eviction, a snapshot of this counter (along with some bits to
175 : * identify the node) is stored in the now empty page cache
176 : * slot of the evicted page. This is called a shadow entry.
177 : *
178 : * On cache misses for which there are shadow entries, an eligible
179 : * refault distance will immediately activate the refaulting page.
180 : */
181 :
182 : #define WORKINGSET_SHIFT 1
183 : #define EVICTION_SHIFT ((BITS_PER_LONG - BITS_PER_XA_VALUE) + \
184 : WORKINGSET_SHIFT + NODES_SHIFT + \
185 : MEM_CGROUP_ID_SHIFT)
186 : #define EVICTION_MASK (~0UL >> EVICTION_SHIFT)
187 :
188 : /*
189 : * Eviction timestamps need to be able to cover the full range of
190 : * actionable refaults. However, bits are tight in the xarray
191 : * entry, and after storing the identifier for the lruvec there might
192 : * not be enough left to represent every single actionable refault. In
193 : * that case, we have to sacrifice granularity for distance, and group
194 : * evictions into coarser buckets by shaving off lower timestamp bits.
195 : */
196 : static unsigned int bucket_order __read_mostly;
197 :
198 0 : static void *pack_shadow(int memcgid, pg_data_t *pgdat, unsigned long eviction,
199 : bool workingset)
200 : {
201 0 : eviction &= EVICTION_MASK;
202 0 : eviction = (eviction << MEM_CGROUP_ID_SHIFT) | memcgid;
203 0 : eviction = (eviction << NODES_SHIFT) | pgdat->node_id;
204 0 : eviction = (eviction << WORKINGSET_SHIFT) | workingset;
205 :
206 0 : return xa_mk_value(eviction);
207 : }
208 :
209 : static void unpack_shadow(void *shadow, int *memcgidp, pg_data_t **pgdat,
210 : unsigned long *evictionp, bool *workingsetp)
211 : {
212 0 : unsigned long entry = xa_to_value(shadow);
213 : int memcgid, nid;
214 : bool workingset;
215 :
216 0 : workingset = entry & ((1UL << WORKINGSET_SHIFT) - 1);
217 0 : entry >>= WORKINGSET_SHIFT;
218 0 : nid = entry & ((1UL << NODES_SHIFT) - 1);
219 0 : entry >>= NODES_SHIFT;
220 0 : memcgid = entry & ((1UL << MEM_CGROUP_ID_SHIFT) - 1);
221 0 : entry >>= MEM_CGROUP_ID_SHIFT;
222 :
223 0 : *memcgidp = memcgid;
224 0 : *pgdat = NODE_DATA(nid);
225 0 : *evictionp = entry;
226 0 : *workingsetp = workingset;
227 : }
228 :
229 : #ifdef CONFIG_LRU_GEN
230 :
231 : static void *lru_gen_eviction(struct folio *folio)
232 : {
233 : int hist;
234 : unsigned long token;
235 : unsigned long min_seq;
236 : struct lruvec *lruvec;
237 : struct lru_gen_folio *lrugen;
238 : int type = folio_is_file_lru(folio);
239 : int delta = folio_nr_pages(folio);
240 : int refs = folio_lru_refs(folio);
241 : int tier = lru_tier_from_refs(refs);
242 : struct mem_cgroup *memcg = folio_memcg(folio);
243 : struct pglist_data *pgdat = folio_pgdat(folio);
244 :
245 : BUILD_BUG_ON(LRU_GEN_WIDTH + LRU_REFS_WIDTH > BITS_PER_LONG - EVICTION_SHIFT);
246 :
247 : lruvec = mem_cgroup_lruvec(memcg, pgdat);
248 : lrugen = &lruvec->lrugen;
249 : min_seq = READ_ONCE(lrugen->min_seq[type]);
250 : token = (min_seq << LRU_REFS_WIDTH) | max(refs - 1, 0);
251 :
252 : hist = lru_hist_from_seq(min_seq);
253 : atomic_long_add(delta, &lrugen->evicted[hist][type][tier]);
254 :
255 : return pack_shadow(mem_cgroup_id(memcg), pgdat, token, refs);
256 : }
257 :
258 : /*
259 : * Tests if the shadow entry is for a folio that was recently evicted.
260 : * Fills in @lruvec, @token, @workingset with the values unpacked from shadow.
261 : */
262 : static bool lru_gen_test_recent(void *shadow, bool file, struct lruvec **lruvec,
263 : unsigned long *token, bool *workingset)
264 : {
265 : int memcg_id;
266 : unsigned long min_seq;
267 : struct mem_cgroup *memcg;
268 : struct pglist_data *pgdat;
269 :
270 : unpack_shadow(shadow, &memcg_id, &pgdat, token, workingset);
271 :
272 : memcg = mem_cgroup_from_id(memcg_id);
273 : *lruvec = mem_cgroup_lruvec(memcg, pgdat);
274 :
275 : min_seq = READ_ONCE((*lruvec)->lrugen.min_seq[file]);
276 : return (*token >> LRU_REFS_WIDTH) == (min_seq & (EVICTION_MASK >> LRU_REFS_WIDTH));
277 : }
278 :
279 : static void lru_gen_refault(struct folio *folio, void *shadow)
280 : {
281 : bool recent;
282 : int hist, tier, refs;
283 : bool workingset;
284 : unsigned long token;
285 : struct lruvec *lruvec;
286 : struct lru_gen_folio *lrugen;
287 : int type = folio_is_file_lru(folio);
288 : int delta = folio_nr_pages(folio);
289 :
290 : rcu_read_lock();
291 :
292 : recent = lru_gen_test_recent(shadow, type, &lruvec, &token, &workingset);
293 : if (lruvec != folio_lruvec(folio))
294 : goto unlock;
295 :
296 : mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + type, delta);
297 :
298 : if (!recent)
299 : goto unlock;
300 :
301 : lrugen = &lruvec->lrugen;
302 :
303 : hist = lru_hist_from_seq(READ_ONCE(lrugen->min_seq[type]));
304 : /* see the comment in folio_lru_refs() */
305 : refs = (token & (BIT(LRU_REFS_WIDTH) - 1)) + workingset;
306 : tier = lru_tier_from_refs(refs);
307 :
308 : atomic_long_add(delta, &lrugen->refaulted[hist][type][tier]);
309 : mod_lruvec_state(lruvec, WORKINGSET_ACTIVATE_BASE + type, delta);
310 :
311 : /*
312 : * Count the following two cases as stalls:
313 : * 1. For pages accessed through page tables, hotter pages pushed out
314 : * hot pages which refaulted immediately.
315 : * 2. For pages accessed multiple times through file descriptors,
316 : * numbers of accesses might have been out of the range.
317 : */
318 : if (lru_gen_in_fault() || refs == BIT(LRU_REFS_WIDTH)) {
319 : folio_set_workingset(folio);
320 : mod_lruvec_state(lruvec, WORKINGSET_RESTORE_BASE + type, delta);
321 : }
322 : unlock:
323 : rcu_read_unlock();
324 : }
325 :
326 : #else /* !CONFIG_LRU_GEN */
327 :
328 : static void *lru_gen_eviction(struct folio *folio)
329 : {
330 : return NULL;
331 : }
332 :
333 : static bool lru_gen_test_recent(void *shadow, bool file, struct lruvec **lruvec,
334 : unsigned long *token, bool *workingset)
335 : {
336 : return false;
337 : }
338 :
339 : static void lru_gen_refault(struct folio *folio, void *shadow)
340 : {
341 : }
342 :
343 : #endif /* CONFIG_LRU_GEN */
344 :
345 : /**
346 : * workingset_age_nonresident - age non-resident entries as LRU ages
347 : * @lruvec: the lruvec that was aged
348 : * @nr_pages: the number of pages to count
349 : *
350 : * As in-memory pages are aged, non-resident pages need to be aged as
351 : * well, in order for the refault distances later on to be comparable
352 : * to the in-memory dimensions. This function allows reclaim and LRU
353 : * operations to drive the non-resident aging along in parallel.
354 : */
355 0 : void workingset_age_nonresident(struct lruvec *lruvec, unsigned long nr_pages)
356 : {
357 : /*
358 : * Reclaiming a cgroup means reclaiming all its children in a
359 : * round-robin fashion. That means that each cgroup has an LRU
360 : * order that is composed of the LRU orders of its child
361 : * cgroups; and every page has an LRU position not just in the
362 : * cgroup that owns it, but in all of that group's ancestors.
363 : *
364 : * So when the physical inactive list of a leaf cgroup ages,
365 : * the virtual inactive lists of all its parents, including
366 : * the root cgroup's, age as well.
367 : */
368 : do {
369 0 : atomic_long_add(nr_pages, &lruvec->nonresident_age);
370 0 : } while ((lruvec = parent_lruvec(lruvec)));
371 0 : }
372 :
373 : /**
374 : * workingset_eviction - note the eviction of a folio from memory
375 : * @target_memcg: the cgroup that is causing the reclaim
376 : * @folio: the folio being evicted
377 : *
378 : * Return: a shadow entry to be stored in @folio->mapping->i_pages in place
379 : * of the evicted @folio so that a later refault can be detected.
380 : */
381 0 : void *workingset_eviction(struct folio *folio, struct mem_cgroup *target_memcg)
382 : {
383 0 : struct pglist_data *pgdat = folio_pgdat(folio);
384 : unsigned long eviction;
385 : struct lruvec *lruvec;
386 : int memcgid;
387 :
388 : /* Folio is fully exclusive and pins folio's memory cgroup pointer */
389 : VM_BUG_ON_FOLIO(folio_test_lru(folio), folio);
390 : VM_BUG_ON_FOLIO(folio_ref_count(folio), folio);
391 : VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
392 :
393 : if (lru_gen_enabled())
394 : return lru_gen_eviction(folio);
395 :
396 0 : lruvec = mem_cgroup_lruvec(target_memcg, pgdat);
397 : /* XXX: target_memcg can be NULL, go through lruvec */
398 0 : memcgid = mem_cgroup_id(lruvec_memcg(lruvec));
399 0 : eviction = atomic_long_read(&lruvec->nonresident_age);
400 0 : eviction >>= bucket_order;
401 0 : workingset_age_nonresident(lruvec, folio_nr_pages(folio));
402 0 : return pack_shadow(memcgid, pgdat, eviction,
403 0 : folio_test_workingset(folio));
404 : }
405 :
406 : /**
407 : * workingset_test_recent - tests if the shadow entry is for a folio that was
408 : * recently evicted. Also fills in @workingset with the value unpacked from
409 : * shadow.
410 : * @shadow: the shadow entry to be tested.
411 : * @file: whether the corresponding folio is from the file lru.
412 : * @workingset: where the workingset value unpacked from shadow should
413 : * be stored.
414 : *
415 : * Return: true if the shadow is for a recently evicted folio; false otherwise.
416 : */
417 0 : bool workingset_test_recent(void *shadow, bool file, bool *workingset)
418 : {
419 : struct mem_cgroup *eviction_memcg;
420 : struct lruvec *eviction_lruvec;
421 : unsigned long refault_distance;
422 : unsigned long workingset_size;
423 : unsigned long refault;
424 : int memcgid;
425 : struct pglist_data *pgdat;
426 : unsigned long eviction;
427 :
428 : if (lru_gen_enabled())
429 : return lru_gen_test_recent(shadow, file, &eviction_lruvec, &eviction, workingset);
430 :
431 0 : unpack_shadow(shadow, &memcgid, &pgdat, &eviction, workingset);
432 0 : eviction <<= bucket_order;
433 :
434 : /*
435 : * Look up the memcg associated with the stored ID. It might
436 : * have been deleted since the folio's eviction.
437 : *
438 : * Note that in rare events the ID could have been recycled
439 : * for a new cgroup that refaults a shared folio. This is
440 : * impossible to tell from the available data. However, this
441 : * should be a rare and limited disturbance, and activations
442 : * are always speculative anyway. Ultimately, it's the aging
443 : * algorithm's job to shake out the minimum access frequency
444 : * for the active cache.
445 : *
446 : * XXX: On !CONFIG_MEMCG, this will always return NULL; it
447 : * would be better if the root_mem_cgroup existed in all
448 : * configurations instead.
449 : */
450 0 : eviction_memcg = mem_cgroup_from_id(memcgid);
451 : if (!mem_cgroup_disabled() && !eviction_memcg)
452 : return false;
453 :
454 0 : eviction_lruvec = mem_cgroup_lruvec(eviction_memcg, pgdat);
455 0 : refault = atomic_long_read(&eviction_lruvec->nonresident_age);
456 :
457 : /*
458 : * Calculate the refault distance
459 : *
460 : * The unsigned subtraction here gives an accurate distance
461 : * across nonresident_age overflows in most cases. There is a
462 : * special case: usually, shadow entries have a short lifetime
463 : * and are either refaulted or reclaimed along with the inode
464 : * before they get too old. But it is not impossible for the
465 : * nonresident_age to lap a shadow entry in the field, which
466 : * can then result in a false small refault distance, leading
467 : * to a false activation should this old entry actually
468 : * refault again. However, earlier kernels used to deactivate
469 : * unconditionally with *every* reclaim invocation for the
470 : * longest time, so the occasional inappropriate activation
471 : * leading to pressure on the active list is not a problem.
472 : */
473 0 : refault_distance = (refault - eviction) & EVICTION_MASK;
474 :
475 : /*
476 : * Compare the distance to the existing workingset size. We
477 : * don't activate pages that couldn't stay resident even if
478 : * all the memory was available to the workingset. Whether
479 : * workingset competition needs to consider anon or not depends
480 : * on having free swap space.
481 : */
482 0 : workingset_size = lruvec_page_state(eviction_lruvec, NR_ACTIVE_FILE);
483 0 : if (!file) {
484 0 : workingset_size += lruvec_page_state(eviction_lruvec,
485 : NR_INACTIVE_FILE);
486 : }
487 0 : if (mem_cgroup_get_nr_swap_pages(eviction_memcg) > 0) {
488 0 : workingset_size += lruvec_page_state(eviction_lruvec,
489 : NR_ACTIVE_ANON);
490 0 : if (file) {
491 0 : workingset_size += lruvec_page_state(eviction_lruvec,
492 : NR_INACTIVE_ANON);
493 : }
494 : }
495 :
496 0 : return refault_distance <= workingset_size;
497 : }
498 :
499 : /**
500 : * workingset_refault - Evaluate the refault of a previously evicted folio.
501 : * @folio: The freshly allocated replacement folio.
502 : * @shadow: Shadow entry of the evicted folio.
503 : *
504 : * Calculates and evaluates the refault distance of the previously
505 : * evicted folio in the context of the node and the memcg whose memory
506 : * pressure caused the eviction.
507 : */
508 0 : void workingset_refault(struct folio *folio, void *shadow)
509 : {
510 0 : bool file = folio_is_file_lru(folio);
511 : struct pglist_data *pgdat;
512 : struct mem_cgroup *memcg;
513 : struct lruvec *lruvec;
514 : bool workingset;
515 : long nr;
516 :
517 : if (lru_gen_enabled()) {
518 : lru_gen_refault(folio, shadow);
519 : return;
520 : }
521 :
522 : /* Flush stats (and potentially sleep) before holding RCU read lock */
523 : mem_cgroup_flush_stats_ratelimited();
524 :
525 : rcu_read_lock();
526 :
527 : /*
528 : * The activation decision for this folio is made at the level
529 : * where the eviction occurred, as that is where the LRU order
530 : * during folio reclaim is being determined.
531 : *
532 : * However, the cgroup that will own the folio is the one that
533 : * is actually experiencing the refault event.
534 : */
535 0 : nr = folio_nr_pages(folio);
536 0 : memcg = folio_memcg(folio);
537 0 : pgdat = folio_pgdat(folio);
538 0 : lruvec = mem_cgroup_lruvec(memcg, pgdat);
539 :
540 0 : mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + file, nr);
541 :
542 0 : if (!workingset_test_recent(shadow, file, &workingset))
543 : goto out;
544 :
545 0 : folio_set_active(folio);
546 0 : workingset_age_nonresident(lruvec, nr);
547 0 : mod_lruvec_state(lruvec, WORKINGSET_ACTIVATE_BASE + file, nr);
548 :
549 : /* Folio was active prior to eviction */
550 0 : if (workingset) {
551 0 : folio_set_workingset(folio);
552 : /*
553 : * XXX: Move to folio_add_lru() when it supports new vs
554 : * putback
555 : */
556 0 : lru_note_cost_refault(folio);
557 0 : mod_lruvec_state(lruvec, WORKINGSET_RESTORE_BASE + file, nr);
558 : }
559 : out:
560 : rcu_read_unlock();
561 : }
562 :
563 : /**
564 : * workingset_activation - note a page activation
565 : * @folio: Folio that is being activated.
566 : */
567 0 : void workingset_activation(struct folio *folio)
568 : {
569 : struct mem_cgroup *memcg;
570 :
571 : rcu_read_lock();
572 : /*
573 : * Filter non-memcg pages here, e.g. unmap can call
574 : * mark_page_accessed() on VDSO pages.
575 : *
576 : * XXX: See workingset_refault() - this should return
577 : * root_mem_cgroup even for !CONFIG_MEMCG.
578 : */
579 0 : memcg = folio_memcg_rcu(folio);
580 : if (!mem_cgroup_disabled() && !memcg)
581 : goto out;
582 0 : workingset_age_nonresident(folio_lruvec(folio), folio_nr_pages(folio));
583 : out:
584 : rcu_read_unlock();
585 0 : }
586 :
587 : /*
588 : * Shadow entries reflect the share of the working set that does not
589 : * fit into memory, so their number depends on the access pattern of
590 : * the workload. In most cases, they will refault or get reclaimed
591 : * along with the inode, but a (malicious) workload that streams
592 : * through files with a total size several times that of available
593 : * memory, while preventing the inodes from being reclaimed, can
594 : * create excessive amounts of shadow nodes. To keep a lid on this,
595 : * track shadow nodes and reclaim them when they grow way past the
596 : * point where they would still be useful.
597 : */
598 :
599 : struct list_lru shadow_nodes;
600 :
601 0 : void workingset_update_node(struct xa_node *node)
602 : {
603 : struct address_space *mapping;
604 :
605 : /*
606 : * Track non-empty nodes that contain only shadow entries;
607 : * unlink those that contain pages or are being freed.
608 : *
609 : * Avoid acquiring the list_lru lock when the nodes are
610 : * already where they should be. The list_empty() test is safe
611 : * as node->private_list is protected by the i_pages lock.
612 : */
613 0 : mapping = container_of(node->array, struct address_space, i_pages);
614 : lockdep_assert_held(&mapping->i_pages.xa_lock);
615 :
616 0 : if (node->count && node->count == node->nr_values) {
617 0 : if (list_empty(&node->private_list)) {
618 0 : list_lru_add(&shadow_nodes, &node->private_list);
619 : __inc_lruvec_kmem_state(node, WORKINGSET_NODES);
620 : }
621 : } else {
622 0 : if (!list_empty(&node->private_list)) {
623 0 : list_lru_del(&shadow_nodes, &node->private_list);
624 : __dec_lruvec_kmem_state(node, WORKINGSET_NODES);
625 : }
626 : }
627 0 : }
628 :
629 0 : static unsigned long count_shadow_nodes(struct shrinker *shrinker,
630 : struct shrink_control *sc)
631 : {
632 : unsigned long max_nodes;
633 : unsigned long nodes;
634 : unsigned long pages;
635 :
636 0 : nodes = list_lru_shrink_count(&shadow_nodes, sc);
637 0 : if (!nodes)
638 : return SHRINK_EMPTY;
639 :
640 : /*
641 : * Approximate a reasonable limit for the nodes
642 : * containing shadow entries. We don't need to keep more
643 : * shadow entries than possible pages on the active list,
644 : * since refault distances bigger than that are dismissed.
645 : *
646 : * The size of the active list converges toward 100% of
647 : * overall page cache as memory grows, with only a tiny
648 : * inactive list. Assume the total cache size for that.
649 : *
650 : * Nodes might be sparsely populated, with only one shadow
651 : * entry in the extreme case. Obviously, we cannot keep one
652 : * node for every eligible shadow entry, so compromise on a
653 : * worst-case density of 1/8th. Below that, not all eligible
654 : * refaults can be detected anymore.
655 : *
656 : * On 64-bit with 7 xa_nodes per page and 64 slots
657 : * each, this will reclaim shadow entries when they consume
658 : * ~1.8% of available memory:
659 : *
660 : * PAGE_SIZE / xa_nodes / node_entries * 8 / PAGE_SIZE
661 : */
662 : #ifdef CONFIG_MEMCG
663 : if (sc->memcg) {
664 : struct lruvec *lruvec;
665 : int i;
666 :
667 : lruvec = mem_cgroup_lruvec(sc->memcg, NODE_DATA(sc->nid));
668 : for (pages = 0, i = 0; i < NR_LRU_LISTS; i++)
669 : pages += lruvec_page_state_local(lruvec,
670 : NR_LRU_BASE + i);
671 : pages += lruvec_page_state_local(
672 : lruvec, NR_SLAB_RECLAIMABLE_B) >> PAGE_SHIFT;
673 : pages += lruvec_page_state_local(
674 : lruvec, NR_SLAB_UNRECLAIMABLE_B) >> PAGE_SHIFT;
675 : } else
676 : #endif
677 0 : pages = node_present_pages(sc->nid);
678 :
679 0 : max_nodes = pages >> (XA_CHUNK_SHIFT - 3);
680 :
681 0 : if (nodes <= max_nodes)
682 : return 0;
683 0 : return nodes - max_nodes;
684 : }
685 :
686 0 : static enum lru_status shadow_lru_isolate(struct list_head *item,
687 : struct list_lru_one *lru,
688 : spinlock_t *lru_lock,
689 : void *arg) __must_hold(lru_lock)
690 : {
691 0 : struct xa_node *node = container_of(item, struct xa_node, private_list);
692 : struct address_space *mapping;
693 : int ret;
694 :
695 : /*
696 : * Page cache insertions and deletions synchronously maintain
697 : * the shadow node LRU under the i_pages lock and the
698 : * lru_lock. Because the page cache tree is emptied before
699 : * the inode can be destroyed, holding the lru_lock pins any
700 : * address_space that has nodes on the LRU.
701 : *
702 : * We can then safely transition to the i_pages lock to
703 : * pin only the address_space of the particular node we want
704 : * to reclaim, take the node off-LRU, and drop the lru_lock.
705 : */
706 :
707 0 : mapping = container_of(node->array, struct address_space, i_pages);
708 :
709 : /* Coming from the list, invert the lock order */
710 0 : if (!xa_trylock(&mapping->i_pages)) {
711 : spin_unlock_irq(lru_lock);
712 : ret = LRU_RETRY;
713 : goto out;
714 : }
715 :
716 : /* For page cache we need to hold i_lock */
717 0 : if (mapping->host != NULL) {
718 0 : if (!spin_trylock(&mapping->host->i_lock)) {
719 : xa_unlock(&mapping->i_pages);
720 : spin_unlock_irq(lru_lock);
721 : ret = LRU_RETRY;
722 : goto out;
723 : }
724 : }
725 :
726 0 : list_lru_isolate(lru, item);
727 0 : __dec_lruvec_kmem_state(node, WORKINGSET_NODES);
728 :
729 0 : spin_unlock(lru_lock);
730 :
731 : /*
732 : * The nodes should only contain one or more shadow entries,
733 : * no pages, so we expect to be able to remove them all and
734 : * delete and free the empty node afterwards.
735 : */
736 0 : if (WARN_ON_ONCE(!node->nr_values))
737 : goto out_invalid;
738 0 : if (WARN_ON_ONCE(node->count != node->nr_values))
739 : goto out_invalid;
740 0 : xa_delete_node(node, workingset_update_node);
741 : __inc_lruvec_kmem_state(node, WORKINGSET_NODERECLAIM);
742 :
743 : out_invalid:
744 0 : xa_unlock_irq(&mapping->i_pages);
745 0 : if (mapping->host != NULL) {
746 0 : if (mapping_shrinkable(mapping))
747 0 : inode_add_lru(mapping->host);
748 0 : spin_unlock(&mapping->host->i_lock);
749 : }
750 0 : ret = LRU_REMOVED_RETRY;
751 : out:
752 0 : cond_resched();
753 0 : spin_lock_irq(lru_lock);
754 0 : return ret;
755 : }
756 :
757 0 : static unsigned long scan_shadow_nodes(struct shrinker *shrinker,
758 : struct shrink_control *sc)
759 : {
760 : /* list_lru lock nests inside the IRQ-safe i_pages lock */
761 0 : return list_lru_shrink_walk_irq(&shadow_nodes, sc, shadow_lru_isolate,
762 : NULL);
763 : }
764 :
765 : static struct shrinker workingset_shadow_shrinker = {
766 : .count_objects = count_shadow_nodes,
767 : .scan_objects = scan_shadow_nodes,
768 : .seeks = 0, /* ->count reports only fully expendable nodes */
769 : .flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE,
770 : };
771 :
772 : /*
773 : * Our list_lru->lock is IRQ-safe as it nests inside the IRQ-safe
774 : * i_pages lock.
775 : */
776 : static struct lock_class_key shadow_nodes_key;
777 :
778 1 : static int __init workingset_init(void)
779 : {
780 : unsigned int timestamp_bits;
781 : unsigned int max_order;
782 : int ret;
783 :
784 : BUILD_BUG_ON(BITS_PER_LONG < EVICTION_SHIFT);
785 : /*
786 : * Calculate the eviction bucket size to cover the longest
787 : * actionable refault distance, which is currently half of
788 : * memory (totalram_pages/2). However, memory hotplug may add
789 : * some more pages at runtime, so keep working with up to
790 : * double the initial memory by using totalram_pages as-is.
791 : */
792 1 : timestamp_bits = BITS_PER_LONG - EVICTION_SHIFT;
793 2 : max_order = fls_long(totalram_pages() - 1);
794 1 : if (max_order > timestamp_bits)
795 0 : bucket_order = max_order - timestamp_bits;
796 1 : pr_info("workingset: timestamp_bits=%d max_order=%d bucket_order=%u\n",
797 : timestamp_bits, max_order, bucket_order);
798 :
799 1 : ret = prealloc_shrinker(&workingset_shadow_shrinker, "mm-shadow");
800 1 : if (ret)
801 : goto err;
802 1 : ret = __list_lru_init(&shadow_nodes, true, &shadow_nodes_key,
803 : &workingset_shadow_shrinker);
804 1 : if (ret)
805 : goto err_list_lru;
806 1 : register_shrinker_prepared(&workingset_shadow_shrinker);
807 1 : return 0;
808 : err_list_lru:
809 0 : free_prealloced_shrinker(&workingset_shadow_shrinker);
810 : err:
811 : return ret;
812 : }
813 : module_init(workingset_init);
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