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
pack_shadow(int memcgid,pg_data_t * pgdat,unsigned long eviction,bool workingset)198 static void *pack_shadow(int memcgid, pg_data_t *pgdat, unsigned long eviction,
199 bool workingset)
200 {
201 eviction &= EVICTION_MASK;
202 eviction = (eviction << MEM_CGROUP_ID_SHIFT) | memcgid;
203 eviction = (eviction << NODES_SHIFT) | pgdat->node_id;
204 eviction = (eviction << WORKINGSET_SHIFT) | workingset;
205
206 return xa_mk_value(eviction);
207 }
208
unpack_shadow(void * shadow,int * memcgidp,pg_data_t ** pgdat,unsigned long * evictionp,bool * workingsetp)209 static void unpack_shadow(void *shadow, int *memcgidp, pg_data_t **pgdat,
210 unsigned long *evictionp, bool *workingsetp)
211 {
212 unsigned long entry = xa_to_value(shadow);
213 int memcgid, nid;
214 bool workingset;
215
216 workingset = entry & ((1UL << WORKINGSET_SHIFT) - 1);
217 entry >>= WORKINGSET_SHIFT;
218 nid = entry & ((1UL << NODES_SHIFT) - 1);
219 entry >>= NODES_SHIFT;
220 memcgid = entry & ((1UL << MEM_CGROUP_ID_SHIFT) - 1);
221 entry >>= MEM_CGROUP_ID_SHIFT;
222
223 *memcgidp = memcgid;
224 *pgdat = NODE_DATA(nid);
225 *evictionp = entry;
226 *workingsetp = workingset;
227 }
228
229 #ifdef CONFIG_LRU_GEN
230
lru_gen_eviction(struct folio * folio)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 */
lru_gen_test_recent(void * shadow,bool file,struct lruvec ** lruvec,unsigned long * token,bool * workingset)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
lru_gen_refault(struct folio * folio,void * shadow)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
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,bool file,struct lruvec ** lruvec,unsigned long * token,bool * workingset)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
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 *
415 * Return: true if the shadow is for a recently evicted folio; false otherwise.
416 */
workingset_test_recent(void * shadow,bool file,bool * workingset)417 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 unpack_shadow(shadow, &memcgid, &pgdat, &eviction, workingset);
432 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 eviction_memcg = mem_cgroup_from_id(memcgid);
451 if (!mem_cgroup_disabled() && !eviction_memcg)
452 return false;
453
454 eviction_lruvec = mem_cgroup_lruvec(eviction_memcg, pgdat);
455 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 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 workingset_size = lruvec_page_state(eviction_lruvec, NR_ACTIVE_FILE);
483 if (!file) {
484 workingset_size += lruvec_page_state(eviction_lruvec,
485 NR_INACTIVE_FILE);
486 }
487 if (mem_cgroup_get_nr_swap_pages(eviction_memcg) > 0) {
488 workingset_size += lruvec_page_state(eviction_lruvec,
489 NR_ACTIVE_ANON);
490 if (file) {
491 workingset_size += lruvec_page_state(eviction_lruvec,
492 NR_INACTIVE_ANON);
493 }
494 }
495
496 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 */
workingset_refault(struct folio * folio,void * shadow)508 void workingset_refault(struct folio *folio, void *shadow)
509 {
510 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 nr = folio_nr_pages(folio);
536 memcg = folio_memcg(folio);
537 pgdat = folio_pgdat(folio);
538 lruvec = mem_cgroup_lruvec(memcg, pgdat);
539
540 mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + file, nr);
541
542 if (!workingset_test_recent(shadow, file, &workingset))
543 goto out;
544
545 folio_set_active(folio);
546 workingset_age_nonresident(lruvec, nr);
547 mod_lruvec_state(lruvec, WORKINGSET_ACTIVATE_BASE + file, nr);
548
549 /* Folio was active prior to eviction */
550 if (workingset) {
551 folio_set_workingset(folio);
552 /*
553 * XXX: Move to folio_add_lru() when it supports new vs
554 * putback
555 */
556 lru_note_cost_refault(folio);
557 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 */
workingset_activation(struct folio * folio)567 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 memcg = folio_memcg_rcu(folio);
580 if (!mem_cgroup_disabled() && !memcg)
581 goto out;
582 workingset_age_nonresident(folio_lruvec(folio), folio_nr_pages(folio));
583 out:
584 rcu_read_unlock();
585 }
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
workingset_update_node(struct xa_node * node)601 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 mapping = container_of(node->array, struct address_space, i_pages);
614 lockdep_assert_held(&mapping->i_pages.xa_lock);
615
616 if (node->count && node->count == node->nr_values) {
617 if (list_empty(&node->private_list)) {
618 list_lru_add(&shadow_nodes, &node->private_list);
619 __inc_lruvec_kmem_state(node, WORKINGSET_NODES);
620 }
621 } else {
622 if (!list_empty(&node->private_list)) {
623 list_lru_del(&shadow_nodes, &node->private_list);
624 __dec_lruvec_kmem_state(node, WORKINGSET_NODES);
625 }
626 }
627 }
628
count_shadow_nodes(struct shrinker * shrinker,struct shrink_control * sc)629 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 nodes = list_lru_shrink_count(&shadow_nodes, sc);
637 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 mem_cgroup_flush_stats();
668 lruvec = mem_cgroup_lruvec(sc->memcg, NODE_DATA(sc->nid));
669 for (pages = 0, i = 0; i < NR_LRU_LISTS; i++)
670 pages += lruvec_page_state_local(lruvec,
671 NR_LRU_BASE + i);
672 pages += lruvec_page_state_local(
673 lruvec, NR_SLAB_RECLAIMABLE_B) >> PAGE_SHIFT;
674 pages += lruvec_page_state_local(
675 lruvec, NR_SLAB_UNRECLAIMABLE_B) >> PAGE_SHIFT;
676 } else
677 #endif
678 pages = node_present_pages(sc->nid);
679
680 max_nodes = pages >> (XA_CHUNK_SHIFT - 3);
681
682 if (nodes <= max_nodes)
683 return 0;
684 return nodes - max_nodes;
685 }
686
shadow_lru_isolate(struct list_head * item,struct list_lru_one * lru,spinlock_t * lru_lock,void * arg)687 static enum lru_status shadow_lru_isolate(struct list_head *item,
688 struct list_lru_one *lru,
689 spinlock_t *lru_lock,
690 void *arg) __must_hold(lru_lock)
691 {
692 struct xa_node *node = container_of(item, struct xa_node, private_list);
693 struct address_space *mapping;
694 int ret;
695
696 /*
697 * Page cache insertions and deletions synchronously maintain
698 * the shadow node LRU under the i_pages lock and the
699 * lru_lock. Because the page cache tree is emptied before
700 * the inode can be destroyed, holding the lru_lock pins any
701 * address_space that has nodes on the LRU.
702 *
703 * We can then safely transition to the i_pages lock to
704 * pin only the address_space of the particular node we want
705 * to reclaim, take the node off-LRU, and drop the lru_lock.
706 */
707
708 mapping = container_of(node->array, struct address_space, i_pages);
709
710 /* Coming from the list, invert the lock order */
711 if (!xa_trylock(&mapping->i_pages)) {
712 spin_unlock_irq(lru_lock);
713 ret = LRU_RETRY;
714 goto out;
715 }
716
717 /* For page cache we need to hold i_lock */
718 if (mapping->host != NULL) {
719 if (!spin_trylock(&mapping->host->i_lock)) {
720 xa_unlock(&mapping->i_pages);
721 spin_unlock_irq(lru_lock);
722 ret = LRU_RETRY;
723 goto out;
724 }
725 }
726
727 list_lru_isolate(lru, item);
728 __dec_lruvec_kmem_state(node, WORKINGSET_NODES);
729
730 spin_unlock(lru_lock);
731
732 /*
733 * The nodes should only contain one or more shadow entries,
734 * no pages, so we expect to be able to remove them all and
735 * delete and free the empty node afterwards.
736 */
737 if (WARN_ON_ONCE(!node->nr_values))
738 goto out_invalid;
739 if (WARN_ON_ONCE(node->count != node->nr_values))
740 goto out_invalid;
741 xa_delete_node(node, workingset_update_node);
742 __inc_lruvec_kmem_state(node, WORKINGSET_NODERECLAIM);
743
744 out_invalid:
745 xa_unlock_irq(&mapping->i_pages);
746 if (mapping->host != NULL) {
747 if (mapping_shrinkable(mapping))
748 inode_add_lru(mapping->host);
749 spin_unlock(&mapping->host->i_lock);
750 }
751 ret = LRU_REMOVED_RETRY;
752 out:
753 cond_resched();
754 spin_lock_irq(lru_lock);
755 return ret;
756 }
757
scan_shadow_nodes(struct shrinker * shrinker,struct shrink_control * sc)758 static unsigned long scan_shadow_nodes(struct shrinker *shrinker,
759 struct shrink_control *sc)
760 {
761 /* list_lru lock nests inside the IRQ-safe i_pages lock */
762 return list_lru_shrink_walk_irq(&shadow_nodes, sc, shadow_lru_isolate,
763 NULL);
764 }
765
766 static struct shrinker workingset_shadow_shrinker = {
767 .count_objects = count_shadow_nodes,
768 .scan_objects = scan_shadow_nodes,
769 .seeks = 0, /* ->count reports only fully expendable nodes */
770 .flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE,
771 };
772
773 /*
774 * Our list_lru->lock is IRQ-safe as it nests inside the IRQ-safe
775 * i_pages lock.
776 */
777 static struct lock_class_key shadow_nodes_key;
778
workingset_init(void)779 static int __init workingset_init(void)
780 {
781 unsigned int timestamp_bits;
782 unsigned int max_order;
783 int ret;
784
785 BUILD_BUG_ON(BITS_PER_LONG < EVICTION_SHIFT);
786 /*
787 * Calculate the eviction bucket size to cover the longest
788 * actionable refault distance, which is currently half of
789 * memory (totalram_pages/2). However, memory hotplug may add
790 * some more pages at runtime, so keep working with up to
791 * double the initial memory by using totalram_pages as-is.
792 */
793 timestamp_bits = BITS_PER_LONG - EVICTION_SHIFT;
794 max_order = fls_long(totalram_pages() - 1);
795 if (max_order > timestamp_bits)
796 bucket_order = max_order - timestamp_bits;
797 pr_info("workingset: timestamp_bits=%d max_order=%d bucket_order=%u\n",
798 timestamp_bits, max_order, bucket_order);
799
800 ret = prealloc_shrinker(&workingset_shadow_shrinker, "mm-shadow");
801 if (ret)
802 goto err;
803 ret = __list_lru_init(&shadow_nodes, true, &shadow_nodes_key,
804 &workingset_shadow_shrinker);
805 if (ret)
806 goto err_list_lru;
807 register_shrinker_prepared(&workingset_shadow_shrinker);
808 return 0;
809 err_list_lru:
810 free_prealloced_shrinker(&workingset_shadow_shrinker);
811 err:
812 return ret;
813 }
814 module_init(workingset_init);
815
