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 #include "internal.h"
20
21 /*
22 * Double CLOCK lists
23 *
24 * Per node, two clock lists are maintained for file pages: the
25 * inactive and the active list. Freshly faulted pages start out at
26 * the head of the inactive list and page reclaim scans pages from the
27 * tail. Pages that are accessed multiple times on the inactive list
28 * are promoted to the active list, to protect them from reclaim,
29 * whereas active pages are demoted to the inactive list when the
30 * active list grows too big.
31 *
32 * fault ------------------------+
33 * |
34 * +--------------+ | +-------------+
35 * reclaim <- | inactive | <-+-- demotion | active | <--+
36 * +--------------+ +-------------+ |
37 * | |
38 * +-------------- promotion ------------------+
39 *
40 *
41 * Access frequency and refault distance
42 *
43 * A workload is thrashing when its pages are frequently used but they
44 * are evicted from the inactive list every time before another access
45 * would have promoted them to the active list.
46 *
47 * In cases where the average access distance between thrashing pages
48 * is bigger than the size of memory there is nothing that can be
49 * done - the thrashing set could never fit into memory under any
50 * circumstance.
51 *
52 * However, the average access distance could be bigger than the
53 * inactive list, yet smaller than the size of memory. In this case,
54 * the set could fit into memory if it weren't for the currently
55 * active pages - which may be used more, hopefully less frequently:
56 *
57 * +-memory available to cache-+
58 * | |
59 * +-inactive------+-active----+
60 * a b | c d e f g h i | J K L M N |
61 * +---------------+-----------+
62 *
63 * It is prohibitively expensive to accurately track access frequency
64 * of pages. But a reasonable approximation can be made to measure
65 * thrashing on the inactive list, after which refaulting pages can be
66 * activated optimistically to compete with the existing active pages.
67 *
68 * Approximating inactive page access frequency - Observations:
69 *
70 * 1. When a page is accessed for the first time, it is added to the
71 * head of the inactive list, slides every existing inactive page
72 * towards the tail by one slot, and pushes the current tail page
73 * out of memory.
74 *
75 * 2. When a page is accessed for the second time, it is promoted to
76 * the active list, shrinking the inactive list by one slot. This
77 * also slides all inactive pages that were faulted into the cache
78 * more recently than the activated page towards the tail of the
79 * inactive list.
80 *
81 * Thus:
82 *
83 * 1. The sum of evictions and activations between any two points in
84 * time indicate the minimum number of inactive pages accessed in
85 * between.
86 *
87 * 2. Moving one inactive page N page slots towards the tail of the
88 * list requires at least N inactive page accesses.
89 *
90 * Combining these:
91 *
92 * 1. When a page is finally evicted from memory, the number of
93 * inactive pages accessed while the page was in cache is at least
94 * the number of page slots on the inactive list.
95 *
96 * 2. In addition, measuring the sum of evictions and activations (E)
97 * at the time of a page's eviction, and comparing it to another
98 * reading (R) at the time the page faults back into memory tells
99 * the minimum number of accesses while the page was not cached.
100 * This is called the refault distance.
101 *
102 * Because the first access of the page was the fault and the second
103 * access the refault, we combine the in-cache distance with the
104 * out-of-cache distance to get the complete minimum access distance
105 * of this page:
106 *
107 * NR_inactive + (R - E)
108 *
109 * And knowing the minimum access distance of a page, we can easily
110 * tell if the page would be able to stay in cache assuming all page
111 * slots in the cache were available:
112 *
113 * NR_inactive + (R - E) <= NR_inactive + NR_active
114 *
115 * If we have swap we should consider about NR_inactive_anon and
116 * NR_active_anon, so for page cache and anonymous respectively:
117 *
118 * NR_inactive_file + (R - E) <= NR_inactive_file + NR_active_file
119 * + NR_inactive_anon + NR_active_anon
120 *
121 * NR_inactive_anon + (R - E) <= NR_inactive_anon + NR_active_anon
122 * + NR_inactive_file + NR_active_file
123 *
124 * Which can be further simplified to:
125 *
126 * (R - E) <= NR_active_file + NR_inactive_anon + NR_active_anon
127 *
128 * (R - E) <= NR_active_anon + NR_inactive_file + NR_active_file
129 *
130 * Put into words, the refault distance (out-of-cache) can be seen as
131 * a deficit in inactive list space (in-cache). If the inactive list
132 * had (R - E) more page slots, the page would not have been evicted
133 * in between accesses, but activated instead. And on a full system,
134 * the only thing eating into inactive list space is active pages.
135 *
136 *
137 * Refaulting inactive pages
138 *
139 * All that is known about the active list is that the pages have been
140 * accessed more than once in the past. This means that at any given
141 * time there is actually a good chance that pages on the active list
142 * are no longer in active use.
143 *
144 * So when a refault distance of (R - E) is observed and there are at
145 * least (R - E) pages in the userspace workingset, the refaulting page
146 * is activated optimistically in the hope that (R - E) pages are actually
147 * used less frequently than the refaulting page - or even not used at
148 * all anymore.
149 *
150 * That means if inactive cache is refaulting with a suitable refault
151 * distance, we assume the cache workingset is transitioning and put
152 * pressure on the current workingset.
153 *
154 * If this is wrong and demotion kicks in, the pages which are truly
155 * used more frequently will be reactivated while the less frequently
156 * used once will be evicted from memory.
157 *
158 * But if this is right, the stale pages will be pushed out of memory
159 * and the used pages get to stay in cache.
160 *
161 * Refaulting active pages
162 *
163 * If on the other hand the refaulting pages have recently been
164 * deactivated, it means that the active list is no longer protecting
165 * actively used cache from reclaim. The cache is NOT transitioning to
166 * a different workingset; the existing workingset is thrashing in the
167 * space allocated to the page cache.
168 *
169 *
170 * Implementation
171 *
172 * For each node's LRU lists, a counter for inactive evictions and
173 * activations is maintained (node->nonresident_age).
174 *
175 * On eviction, a snapshot of this counter (along with some bits to
176 * identify the node) is stored in the now empty page cache
177 * slot of the evicted page. This is called a shadow entry.
178 *
179 * On cache misses for which there are shadow entries, an eligible
180 * refault distance will immediately activate the refaulting page.
181 */
182
183 #define WORKINGSET_SHIFT 1
184 #define EVICTION_SHIFT ((BITS_PER_LONG - BITS_PER_XA_VALUE) + \
185 WORKINGSET_SHIFT + NODES_SHIFT + \
186 MEM_CGROUP_ID_SHIFT)
187 #define EVICTION_MASK (~0UL >> EVICTION_SHIFT)
188
189 /*
190 * Eviction timestamps need to be able to cover the full range of
191 * actionable refaults. However, bits are tight in the xarray
192 * entry, and after storing the identifier for the lruvec there might
193 * not be enough left to represent every single actionable refault. In
194 * that case, we have to sacrifice granularity for distance, and group
195 * evictions into coarser buckets by shaving off lower timestamp bits.
196 */
197 static unsigned int bucket_order __read_mostly;
198
pack_shadow(int memcgid,pg_data_t * pgdat,unsigned long eviction,bool workingset)199 static void *pack_shadow(int memcgid, pg_data_t *pgdat, unsigned long eviction,
200 bool workingset)
201 {
202 eviction &= EVICTION_MASK;
203 eviction = (eviction << MEM_CGROUP_ID_SHIFT) | memcgid;
204 eviction = (eviction << NODES_SHIFT) | pgdat->node_id;
205 eviction = (eviction << WORKINGSET_SHIFT) | workingset;
206
207 return xa_mk_value(eviction);
208 }
209
unpack_shadow(void * shadow,int * memcgidp,pg_data_t ** pgdat,unsigned long * evictionp,bool * workingsetp)210 static void unpack_shadow(void *shadow, int *memcgidp, pg_data_t **pgdat,
211 unsigned long *evictionp, bool *workingsetp)
212 {
213 unsigned long entry = xa_to_value(shadow);
214 int memcgid, nid;
215 bool workingset;
216
217 workingset = entry & ((1UL << WORKINGSET_SHIFT) - 1);
218 entry >>= WORKINGSET_SHIFT;
219 nid = entry & ((1UL << NODES_SHIFT) - 1);
220 entry >>= NODES_SHIFT;
221 memcgid = entry & ((1UL << MEM_CGROUP_ID_SHIFT) - 1);
222 entry >>= MEM_CGROUP_ID_SHIFT;
223
224 *memcgidp = memcgid;
225 *pgdat = NODE_DATA(nid);
226 *evictionp = entry;
227 *workingsetp = workingset;
228 }
229
230 #ifdef CONFIG_LRU_GEN
231
lru_gen_eviction(struct folio * folio)232 static void *lru_gen_eviction(struct folio *folio)
233 {
234 int hist;
235 unsigned long token;
236 unsigned long min_seq;
237 struct lruvec *lruvec;
238 struct lru_gen_folio *lrugen;
239 int type = folio_is_file_lru(folio);
240 int delta = folio_nr_pages(folio);
241 int refs = folio_lru_refs(folio);
242 bool workingset = folio_test_workingset(folio);
243 int tier = lru_tier_from_refs(refs, workingset);
244 struct mem_cgroup *memcg = folio_memcg(folio);
245 struct pglist_data *pgdat = folio_pgdat(folio);
246
247 BUILD_BUG_ON(LRU_GEN_WIDTH + LRU_REFS_WIDTH > BITS_PER_LONG - EVICTION_SHIFT);
248
249 lruvec = mem_cgroup_lruvec(memcg, pgdat);
250 lrugen = &lruvec->lrugen;
251 min_seq = READ_ONCE(lrugen->min_seq[type]);
252 token = (min_seq << LRU_REFS_WIDTH) | max(refs - 1, 0);
253
254 hist = lru_hist_from_seq(min_seq);
255 atomic_long_add(delta, &lrugen->evicted[hist][type][tier]);
256
257 return pack_shadow(mem_cgroup_id(memcg), pgdat, token, workingset);
258 }
259
260 /*
261 * Tests if the shadow entry is for a folio that was recently evicted.
262 * Fills in @lruvec, @token, @workingset with the values unpacked from shadow.
263 */
lru_gen_test_recent(void * shadow,struct lruvec ** lruvec,unsigned long * token,bool * workingset)264 static bool lru_gen_test_recent(void *shadow, struct lruvec **lruvec,
265 unsigned long *token, bool *workingset)
266 {
267 int memcg_id;
268 unsigned long max_seq;
269 struct mem_cgroup *memcg;
270 struct pglist_data *pgdat;
271
272 unpack_shadow(shadow, &memcg_id, &pgdat, token, workingset);
273
274 memcg = mem_cgroup_from_id(memcg_id);
275 *lruvec = mem_cgroup_lruvec(memcg, pgdat);
276
277 max_seq = READ_ONCE((*lruvec)->lrugen.max_seq);
278 max_seq &= EVICTION_MASK >> LRU_REFS_WIDTH;
279
280 return abs_diff(max_seq, *token >> LRU_REFS_WIDTH) < MAX_NR_GENS;
281 }
282
lru_gen_refault(struct folio * folio,void * shadow)283 static void lru_gen_refault(struct folio *folio, void *shadow)
284 {
285 bool recent;
286 int hist, tier, refs;
287 bool workingset;
288 unsigned long token;
289 struct lruvec *lruvec;
290 struct lru_gen_folio *lrugen;
291 int type = folio_is_file_lru(folio);
292 int delta = folio_nr_pages(folio);
293
294 rcu_read_lock();
295
296 recent = lru_gen_test_recent(shadow, &lruvec, &token, &workingset);
297 if (lruvec != folio_lruvec(folio))
298 goto unlock;
299
300 mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + type, delta);
301
302 if (!recent)
303 goto unlock;
304
305 lrugen = &lruvec->lrugen;
306
307 hist = lru_hist_from_seq(READ_ONCE(lrugen->min_seq[type]));
308 refs = (token & (BIT(LRU_REFS_WIDTH) - 1)) + 1;
309 tier = lru_tier_from_refs(refs, workingset);
310
311 atomic_long_add(delta, &lrugen->refaulted[hist][type][tier]);
312
313 /* see folio_add_lru() where folio_set_active() will be called */
314 if (lru_gen_in_fault())
315 mod_lruvec_state(lruvec, WORKINGSET_ACTIVATE_BASE + type, delta);
316
317 if (workingset) {
318 folio_set_workingset(folio);
319 mod_lruvec_state(lruvec, WORKINGSET_RESTORE_BASE + type, delta);
320 } else
321 set_mask_bits(&folio->flags, LRU_REFS_MASK, (refs - 1UL) << LRU_REFS_PGOFF);
322 unlock:
323 rcu_read_unlock();
324 }
325
326 #else /* !CONFIG_LRU_GEN */
327
lru_gen_eviction(struct folio * folio)328 static void *lru_gen_eviction(struct folio *folio)
329 {
330 return NULL;
331 }
332
lru_gen_test_recent(void * shadow,struct lruvec ** lruvec,unsigned long * token,bool * workingset)333 static bool lru_gen_test_recent(void *shadow, struct lruvec **lruvec,
334 unsigned long *token, bool *workingset)
335 {
336 return false;
337 }
338
lru_gen_refault(struct folio * folio,void * shadow)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 */
workingset_age_nonresident(struct lruvec * lruvec,unsigned long nr_pages)355 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 atomic_long_add(nr_pages, &lruvec->nonresident_age);
370 } while ((lruvec = parent_lruvec(lruvec)));
371 }
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 */
workingset_eviction(struct folio * folio,struct mem_cgroup * target_memcg)381 void *workingset_eviction(struct folio *folio, struct mem_cgroup *target_memcg)
382 {
383 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 lruvec = mem_cgroup_lruvec(target_memcg, pgdat);
397 /* XXX: target_memcg can be NULL, go through lruvec */
398 memcgid = mem_cgroup_id(lruvec_memcg(lruvec));
399 eviction = atomic_long_read(&lruvec->nonresident_age);
400 eviction >>= bucket_order;
401 workingset_age_nonresident(lruvec, folio_nr_pages(folio));
402 return pack_shadow(memcgid, pgdat, eviction,
403 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 * @flush: whether to flush cgroup rstat.
415 *
416 * Return: true if the shadow is for a recently evicted folio; false otherwise.
417 */
workingset_test_recent(void * shadow,bool file,bool * workingset,bool flush)418 bool workingset_test_recent(void *shadow, bool file, bool *workingset,
419 bool flush)
420 {
421 struct mem_cgroup *eviction_memcg;
422 struct lruvec *eviction_lruvec;
423 unsigned long refault_distance;
424 unsigned long workingset_size;
425 unsigned long refault;
426 int memcgid;
427 struct pglist_data *pgdat;
428 unsigned long eviction;
429
430 if (lru_gen_enabled()) {
431 bool recent;
432
433 rcu_read_lock();
434 recent = lru_gen_test_recent(shadow, &eviction_lruvec, &eviction, workingset);
435 rcu_read_unlock();
436 return recent;
437 }
438
439 rcu_read_lock();
440 unpack_shadow(shadow, &memcgid, &pgdat, &eviction, workingset);
441 eviction <<= bucket_order;
442
443 /*
444 * Look up the memcg associated with the stored ID. It might
445 * have been deleted since the folio's eviction.
446 *
447 * Note that in rare events the ID could have been recycled
448 * for a new cgroup that refaults a shared folio. This is
449 * impossible to tell from the available data. However, this
450 * should be a rare and limited disturbance, and activations
451 * are always speculative anyway. Ultimately, it's the aging
452 * algorithm's job to shake out the minimum access frequency
453 * for the active cache.
454 *
455 * XXX: On !CONFIG_MEMCG, this will always return NULL; it
456 * would be better if the root_mem_cgroup existed in all
457 * configurations instead.
458 */
459 eviction_memcg = mem_cgroup_from_id(memcgid);
460 if (!mem_cgroup_tryget(eviction_memcg))
461 eviction_memcg = NULL;
462 rcu_read_unlock();
463
464 if (!mem_cgroup_disabled() && !eviction_memcg)
465 return false;
466 /*
467 * Flush stats (and potentially sleep) outside the RCU read section.
468 *
469 * Note that workingset_test_recent() itself might be called in RCU read
470 * section (for e.g, in cachestat) - these callers need to skip flushing
471 * stats (via the flush argument).
472 *
473 * XXX: With per-memcg flushing and thresholding, is ratelimiting
474 * still needed here?
475 */
476 if (flush)
477 mem_cgroup_flush_stats_ratelimited(eviction_memcg);
478
479 eviction_lruvec = mem_cgroup_lruvec(eviction_memcg, pgdat);
480 refault = atomic_long_read(&eviction_lruvec->nonresident_age);
481
482 /*
483 * Calculate the refault distance
484 *
485 * The unsigned subtraction here gives an accurate distance
486 * across nonresident_age overflows in most cases. There is a
487 * special case: usually, shadow entries have a short lifetime
488 * and are either refaulted or reclaimed along with the inode
489 * before they get too old. But it is not impossible for the
490 * nonresident_age to lap a shadow entry in the field, which
491 * can then result in a false small refault distance, leading
492 * to a false activation should this old entry actually
493 * refault again. However, earlier kernels used to deactivate
494 * unconditionally with *every* reclaim invocation for the
495 * longest time, so the occasional inappropriate activation
496 * leading to pressure on the active list is not a problem.
497 */
498 refault_distance = (refault - eviction) & EVICTION_MASK;
499
500 /*
501 * Compare the distance to the existing workingset size. We
502 * don't activate pages that couldn't stay resident even if
503 * all the memory was available to the workingset. Whether
504 * workingset competition needs to consider anon or not depends
505 * on having free swap space.
506 */
507 workingset_size = lruvec_page_state(eviction_lruvec, NR_ACTIVE_FILE);
508 if (!file) {
509 workingset_size += lruvec_page_state(eviction_lruvec,
510 NR_INACTIVE_FILE);
511 }
512 if (mem_cgroup_get_nr_swap_pages(eviction_memcg) > 0) {
513 workingset_size += lruvec_page_state(eviction_lruvec,
514 NR_ACTIVE_ANON);
515 if (file) {
516 workingset_size += lruvec_page_state(eviction_lruvec,
517 NR_INACTIVE_ANON);
518 }
519 }
520
521 mem_cgroup_put(eviction_memcg);
522 return refault_distance <= workingset_size;
523 }
524
525 /**
526 * workingset_refault - Evaluate the refault of a previously evicted folio.
527 * @folio: The freshly allocated replacement folio.
528 * @shadow: Shadow entry of the evicted folio.
529 *
530 * Calculates and evaluates the refault distance of the previously
531 * evicted folio in the context of the node and the memcg whose memory
532 * pressure caused the eviction.
533 */
workingset_refault(struct folio * folio,void * shadow)534 void workingset_refault(struct folio *folio, void *shadow)
535 {
536 bool file = folio_is_file_lru(folio);
537 struct pglist_data *pgdat;
538 struct mem_cgroup *memcg;
539 struct lruvec *lruvec;
540 bool workingset;
541 long nr;
542
543 VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
544
545 if (lru_gen_enabled()) {
546 lru_gen_refault(folio, shadow);
547 return;
548 }
549
550 /*
551 * The activation decision for this folio is made at the level
552 * where the eviction occurred, as that is where the LRU order
553 * during folio reclaim is being determined.
554 *
555 * However, the cgroup that will own the folio is the one that
556 * is actually experiencing the refault event. Make sure the folio is
557 * locked to guarantee folio_memcg() stability throughout.
558 */
559 nr = folio_nr_pages(folio);
560 memcg = folio_memcg(folio);
561 pgdat = folio_pgdat(folio);
562 lruvec = mem_cgroup_lruvec(memcg, pgdat);
563
564 mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + file, nr);
565
566 if (!workingset_test_recent(shadow, file, &workingset, true))
567 return;
568
569 folio_set_active(folio);
570 workingset_age_nonresident(lruvec, nr);
571 mod_lruvec_state(lruvec, WORKINGSET_ACTIVATE_BASE + file, nr);
572
573 /* Folio was active prior to eviction */
574 if (workingset) {
575 folio_set_workingset(folio);
576 /*
577 * XXX: Move to folio_add_lru() when it supports new vs
578 * putback
579 */
580 lru_note_cost_refault(folio);
581 mod_lruvec_state(lruvec, WORKINGSET_RESTORE_BASE + file, nr);
582 }
583 }
584
585 /**
586 * workingset_activation - note a page activation
587 * @folio: Folio that is being activated.
588 */
workingset_activation(struct folio * folio)589 void workingset_activation(struct folio *folio)
590 {
591 /*
592 * Filter non-memcg pages here, e.g. unmap can call
593 * mark_page_accessed() on VDSO pages.
594 */
595 if (mem_cgroup_disabled() || folio_memcg_charged(folio))
596 workingset_age_nonresident(folio_lruvec(folio), folio_nr_pages(folio));
597 }
598
599 /*
600 * Shadow entries reflect the share of the working set that does not
601 * fit into memory, so their number depends on the access pattern of
602 * the workload. In most cases, they will refault or get reclaimed
603 * along with the inode, but a (malicious) workload that streams
604 * through files with a total size several times that of available
605 * memory, while preventing the inodes from being reclaimed, can
606 * create excessive amounts of shadow nodes. To keep a lid on this,
607 * track shadow nodes and reclaim them when they grow way past the
608 * point where they would still be useful.
609 */
610
611 struct list_lru shadow_nodes;
612
workingset_update_node(struct xa_node * node)613 void workingset_update_node(struct xa_node *node)
614 {
615 struct address_space *mapping;
616 struct page *page = virt_to_page(node);
617
618 /*
619 * Track non-empty nodes that contain only shadow entries;
620 * unlink those that contain pages or are being freed.
621 *
622 * Avoid acquiring the list_lru lock when the nodes are
623 * already where they should be. The list_empty() test is safe
624 * as node->private_list is protected by the i_pages lock.
625 */
626 mapping = container_of(node->array, struct address_space, i_pages);
627 lockdep_assert_held(&mapping->i_pages.xa_lock);
628
629 if (node->count && node->count == node->nr_values) {
630 if (list_empty(&node->private_list)) {
631 list_lru_add_obj(&shadow_nodes, &node->private_list);
632 __inc_node_page_state(page, WORKINGSET_NODES);
633 }
634 } else {
635 if (!list_empty(&node->private_list)) {
636 list_lru_del_obj(&shadow_nodes, &node->private_list);
637 __dec_node_page_state(page, WORKINGSET_NODES);
638 }
639 }
640 }
641
count_shadow_nodes(struct shrinker * shrinker,struct shrink_control * sc)642 static unsigned long count_shadow_nodes(struct shrinker *shrinker,
643 struct shrink_control *sc)
644 {
645 unsigned long max_nodes;
646 unsigned long nodes;
647 unsigned long pages;
648
649 nodes = list_lru_shrink_count(&shadow_nodes, sc);
650 if (!nodes)
651 return SHRINK_EMPTY;
652
653 /*
654 * Approximate a reasonable limit for the nodes
655 * containing shadow entries. We don't need to keep more
656 * shadow entries than possible pages on the active list,
657 * since refault distances bigger than that are dismissed.
658 *
659 * The size of the active list converges toward 100% of
660 * overall page cache as memory grows, with only a tiny
661 * inactive list. Assume the total cache size for that.
662 *
663 * Nodes might be sparsely populated, with only one shadow
664 * entry in the extreme case. Obviously, we cannot keep one
665 * node for every eligible shadow entry, so compromise on a
666 * worst-case density of 1/8th. Below that, not all eligible
667 * refaults can be detected anymore.
668 *
669 * On 64-bit with 7 xa_nodes per page and 64 slots
670 * each, this will reclaim shadow entries when they consume
671 * ~1.8% of available memory:
672 *
673 * PAGE_SIZE / xa_nodes / node_entries * 8 / PAGE_SIZE
674 */
675 #ifdef CONFIG_MEMCG
676 if (sc->memcg) {
677 struct lruvec *lruvec;
678 int i;
679
680 mem_cgroup_flush_stats_ratelimited(sc->memcg);
681 lruvec = mem_cgroup_lruvec(sc->memcg, NODE_DATA(sc->nid));
682 for (pages = 0, i = 0; i < NR_LRU_LISTS; i++)
683 pages += lruvec_page_state_local(lruvec,
684 NR_LRU_BASE + i);
685 pages += lruvec_page_state_local(
686 lruvec, NR_SLAB_RECLAIMABLE_B) >> PAGE_SHIFT;
687 pages += lruvec_page_state_local(
688 lruvec, NR_SLAB_UNRECLAIMABLE_B) >> PAGE_SHIFT;
689 } else
690 #endif
691 pages = node_present_pages(sc->nid);
692
693 max_nodes = pages >> (XA_CHUNK_SHIFT - 3);
694
695 if (nodes <= max_nodes)
696 return 0;
697 return nodes - max_nodes;
698 }
699
shadow_lru_isolate(struct list_head * item,struct list_lru_one * lru,void * arg)700 static enum lru_status shadow_lru_isolate(struct list_head *item,
701 struct list_lru_one *lru,
702 void *arg) __must_hold(lru->lock)
703 {
704 struct xa_node *node = container_of(item, struct xa_node, private_list);
705 struct address_space *mapping;
706 int ret;
707
708 /*
709 * Page cache insertions and deletions synchronously maintain
710 * the shadow node LRU under the i_pages lock and the
711 * &lru->lock. Because the page cache tree is emptied before
712 * the inode can be destroyed, holding the &lru->lock pins any
713 * address_space that has nodes on the LRU.
714 *
715 * We can then safely transition to the i_pages lock to
716 * pin only the address_space of the particular node we want
717 * to reclaim, take the node off-LRU, and drop the &lru->lock.
718 */
719
720 mapping = container_of(node->array, struct address_space, i_pages);
721
722 /* Coming from the list, invert the lock order */
723 if (!xa_trylock(&mapping->i_pages)) {
724 spin_unlock_irq(&lru->lock);
725 ret = LRU_RETRY;
726 goto out;
727 }
728
729 /* For page cache we need to hold i_lock */
730 if (mapping->host != NULL) {
731 if (!spin_trylock(&mapping->host->i_lock)) {
732 xa_unlock(&mapping->i_pages);
733 spin_unlock_irq(&lru->lock);
734 ret = LRU_RETRY;
735 goto out;
736 }
737 }
738
739 list_lru_isolate(lru, item);
740 __dec_node_page_state(virt_to_page(node), WORKINGSET_NODES);
741
742 spin_unlock(&lru->lock);
743
744 /*
745 * The nodes should only contain one or more shadow entries,
746 * no pages, so we expect to be able to remove them all and
747 * delete and free the empty node afterwards.
748 */
749 if (WARN_ON_ONCE(!node->nr_values))
750 goto out_invalid;
751 if (WARN_ON_ONCE(node->count != node->nr_values))
752 goto out_invalid;
753 xa_delete_node(node, workingset_update_node);
754 __inc_lruvec_kmem_state(node, WORKINGSET_NODERECLAIM);
755
756 out_invalid:
757 xa_unlock_irq(&mapping->i_pages);
758 if (mapping->host != NULL) {
759 if (mapping_shrinkable(mapping))
760 inode_add_lru(mapping->host);
761 spin_unlock(&mapping->host->i_lock);
762 }
763 ret = LRU_REMOVED_RETRY;
764 out:
765 cond_resched();
766 return ret;
767 }
768
scan_shadow_nodes(struct shrinker * shrinker,struct shrink_control * sc)769 static unsigned long scan_shadow_nodes(struct shrinker *shrinker,
770 struct shrink_control *sc)
771 {
772 /* list_lru lock nests inside the IRQ-safe i_pages lock */
773 return list_lru_shrink_walk_irq(&shadow_nodes, sc, shadow_lru_isolate,
774 NULL);
775 }
776
777 /*
778 * Our list_lru->lock is IRQ-safe as it nests inside the IRQ-safe
779 * i_pages lock.
780 */
781 static struct lock_class_key shadow_nodes_key;
782
workingset_init(void)783 static int __init workingset_init(void)
784 {
785 struct shrinker *workingset_shadow_shrinker;
786 unsigned int timestamp_bits;
787 unsigned int max_order;
788 int ret = -ENOMEM;
789
790 BUILD_BUG_ON(BITS_PER_LONG < EVICTION_SHIFT);
791 /*
792 * Calculate the eviction bucket size to cover the longest
793 * actionable refault distance, which is currently half of
794 * memory (totalram_pages/2). However, memory hotplug may add
795 * some more pages at runtime, so keep working with up to
796 * double the initial memory by using totalram_pages as-is.
797 */
798 timestamp_bits = BITS_PER_LONG - EVICTION_SHIFT;
799 max_order = fls_long(totalram_pages() - 1);
800 if (max_order > timestamp_bits)
801 bucket_order = max_order - timestamp_bits;
802 pr_info("workingset: timestamp_bits=%d max_order=%d bucket_order=%u\n",
803 timestamp_bits, max_order, bucket_order);
804
805 workingset_shadow_shrinker = shrinker_alloc(SHRINKER_NUMA_AWARE |
806 SHRINKER_MEMCG_AWARE,
807 "mm-shadow");
808 if (!workingset_shadow_shrinker)
809 goto err;
810
811 ret = list_lru_init_memcg_key(&shadow_nodes, workingset_shadow_shrinker,
812 &shadow_nodes_key);
813 if (ret)
814 goto err_list_lru;
815
816 workingset_shadow_shrinker->count_objects = count_shadow_nodes;
817 workingset_shadow_shrinker->scan_objects = scan_shadow_nodes;
818 /* ->count reports only fully expendable nodes */
819 workingset_shadow_shrinker->seeks = 0;
820
821 shrinker_register(workingset_shadow_shrinker);
822 return 0;
823 err_list_lru:
824 shrinker_free(workingset_shadow_shrinker);
825 err:
826 return ret;
827 }
828 module_init(workingset_init);
829