Line data Source code
1 : // SPDX-License-Identifier: GPL-2.0
2 : /*
3 : * Workingset detection
4 : *
5 : * Copyright (C) 2013 Red Hat, Inc., Johannes Weiner
6 : */
7 :
8 : #include <linux/memcontrol.h>
9 : #include <linux/mm_inline.h>
10 : #include <linux/writeback.h>
11 : #include <linux/shmem_fs.h>
12 : #include <linux/pagemap.h>
13 : #include <linux/atomic.h>
14 : #include <linux/module.h>
15 : #include <linux/swap.h>
16 : #include <linux/dax.h>
17 : #include <linux/fs.h>
18 : #include <linux/mm.h>
19 :
20 : /*
21 : * Double CLOCK lists
22 : *
23 : * Per node, two clock lists are maintained for file pages: the
24 : * inactive and the active list. Freshly faulted pages start out at
25 : * the head of the inactive list and page reclaim scans pages from the
26 : * tail. Pages that are accessed multiple times on the inactive list
27 : * are promoted to the active list, to protect them from reclaim,
28 : * whereas active pages are demoted to the inactive list when the
29 : * active list grows too big.
30 : *
31 : * fault ------------------------+
32 : * |
33 : * +--------------+ | +-------------+
34 : * reclaim <- | inactive | <-+-- demotion | active | <--+
35 : * +--------------+ +-------------+ |
36 : * | |
37 : * +-------------- promotion ------------------+
38 : *
39 : *
40 : * Access frequency and refault distance
41 : *
42 : * A workload is thrashing when its pages are frequently used but they
43 : * are evicted from the inactive list every time before another access
44 : * would have promoted them to the active list.
45 : *
46 : * In cases where the average access distance between thrashing pages
47 : * is bigger than the size of memory there is nothing that can be
48 : * done - the thrashing set could never fit into memory under any
49 : * circumstance.
50 : *
51 : * However, the average access distance could be bigger than the
52 : * inactive list, yet smaller than the size of memory. In this case,
53 : * the set could fit into memory if it weren't for the currently
54 : * active pages - which may be used more, hopefully less frequently:
55 : *
56 : * +-memory available to cache-+
57 : * | |
58 : * +-inactive------+-active----+
59 : * a b | c d e f g h i | J K L M N |
60 : * +---------------+-----------+
61 : *
62 : * It is prohibitively expensive to accurately track access frequency
63 : * of pages. But a reasonable approximation can be made to measure
64 : * thrashing on the inactive list, after which refaulting pages can be
65 : * activated optimistically to compete with the existing active pages.
66 : *
67 : * Approximating inactive page access frequency - Observations:
68 : *
69 : * 1. When a page is accessed for the first time, it is added to the
70 : * head of the inactive list, slides every existing inactive page
71 : * towards the tail by one slot, and pushes the current tail page
72 : * out of memory.
73 : *
74 : * 2. When a page is accessed for the second time, it is promoted to
75 : * the active list, shrinking the inactive list by one slot. This
76 : * also slides all inactive pages that were faulted into the cache
77 : * more recently than the activated page towards the tail of the
78 : * inactive list.
79 : *
80 : * Thus:
81 : *
82 : * 1. The sum of evictions and activations between any two points in
83 : * time indicate the minimum number of inactive pages accessed in
84 : * between.
85 : *
86 : * 2. Moving one inactive page N page slots towards the tail of the
87 : * list requires at least N inactive page accesses.
88 : *
89 : * Combining these:
90 : *
91 : * 1. When a page is finally evicted from memory, the number of
92 : * inactive pages accessed while the page was in cache is at least
93 : * the number of page slots on the inactive list.
94 : *
95 : * 2. In addition, measuring the sum of evictions and activations (E)
96 : * at the time of a page's eviction, and comparing it to another
97 : * reading (R) at the time the page faults back into memory tells
98 : * the minimum number of accesses while the page was not cached.
99 : * This is called the refault distance.
100 : *
101 : * Because the first access of the page was the fault and the second
102 : * access the refault, we combine the in-cache distance with the
103 : * out-of-cache distance to get the complete minimum access distance
104 : * of this page:
105 : *
106 : * NR_inactive + (R - E)
107 : *
108 : * And knowing the minimum access distance of a page, we can easily
109 : * tell if the page would be able to stay in cache assuming all page
110 : * slots in the cache were available:
111 : *
112 : * NR_inactive + (R - E) <= NR_inactive + NR_active
113 : *
114 : * which can be further simplified to
115 : *
116 : * (R - E) <= NR_active
117 : *
118 : * Put into words, the refault distance (out-of-cache) can be seen as
119 : * a deficit in inactive list space (in-cache). If the inactive list
120 : * had (R - E) more page slots, the page would not have been evicted
121 : * in between accesses, but activated instead. And on a full system,
122 : * the only thing eating into inactive list space is active pages.
123 : *
124 : *
125 : * Refaulting inactive pages
126 : *
127 : * All that is known about the active list is that the pages have been
128 : * accessed more than once in the past. This means that at any given
129 : * time there is actually a good chance that pages on the active list
130 : * are no longer in active use.
131 : *
132 : * So when a refault distance of (R - E) is observed and there are at
133 : * least (R - E) active pages, the refaulting page is activated
134 : * optimistically in the hope that (R - E) active pages are actually
135 : * used less frequently than the refaulting page - or even not used at
136 : * all anymore.
137 : *
138 : * That means if inactive cache is refaulting with a suitable refault
139 : * distance, we assume the cache workingset is transitioning and put
140 : * pressure on the current active list.
141 : *
142 : * If this is wrong and demotion kicks in, the pages which are truly
143 : * used more frequently will be reactivated while the less frequently
144 : * used once will be evicted from memory.
145 : *
146 : * But if this is right, the stale pages will be pushed out of memory
147 : * and the used pages get to stay in cache.
148 : *
149 : * Refaulting active pages
150 : *
151 : * If on the other hand the refaulting pages have recently been
152 : * deactivated, it means that the active list is no longer protecting
153 : * actively used cache from reclaim. The cache is NOT transitioning to
154 : * a different workingset; the existing workingset is thrashing in the
155 : * space allocated to the page cache.
156 : *
157 : *
158 : * Implementation
159 : *
160 : * For each node's LRU lists, a counter for inactive evictions and
161 : * activations is maintained (node->nonresident_age).
162 : *
163 : * On eviction, a snapshot of this counter (along with some bits to
164 : * identify the node) is stored in the now empty page cache
165 : * slot of the evicted page. This is called a shadow entry.
166 : *
167 : * On cache misses for which there are shadow entries, an eligible
168 : * refault distance will immediately activate the refaulting page.
169 : */
170 :
171 : #define WORKINGSET_SHIFT 1
172 : #define EVICTION_SHIFT ((BITS_PER_LONG - BITS_PER_XA_VALUE) + \
173 : WORKINGSET_SHIFT + NODES_SHIFT + \
174 : MEM_CGROUP_ID_SHIFT)
175 : #define EVICTION_MASK (~0UL >> EVICTION_SHIFT)
176 :
177 : /*
178 : * Eviction timestamps need to be able to cover the full range of
179 : * actionable refaults. However, bits are tight in the xarray
180 : * entry, and after storing the identifier for the lruvec there might
181 : * not be enough left to represent every single actionable refault. In
182 : * that case, we have to sacrifice granularity for distance, and group
183 : * evictions into coarser buckets by shaving off lower timestamp bits.
184 : */
185 : static unsigned int bucket_order __read_mostly;
186 :
187 0 : static void *pack_shadow(int memcgid, pg_data_t *pgdat, unsigned long eviction,
188 : bool workingset)
189 : {
190 0 : eviction >>= bucket_order;
191 0 : eviction &= EVICTION_MASK;
192 0 : eviction = (eviction << MEM_CGROUP_ID_SHIFT) | memcgid;
193 0 : eviction = (eviction << NODES_SHIFT) | pgdat->node_id;
194 0 : eviction = (eviction << WORKINGSET_SHIFT) | workingset;
195 :
196 0 : return xa_mk_value(eviction);
197 : }
198 :
199 : static void unpack_shadow(void *shadow, int *memcgidp, pg_data_t **pgdat,
200 : unsigned long *evictionp, bool *workingsetp)
201 : {
202 0 : unsigned long entry = xa_to_value(shadow);
203 : int memcgid, nid;
204 : bool workingset;
205 :
206 0 : workingset = entry & ((1UL << WORKINGSET_SHIFT) - 1);
207 0 : entry >>= WORKINGSET_SHIFT;
208 0 : nid = entry & ((1UL << NODES_SHIFT) - 1);
209 0 : entry >>= NODES_SHIFT;
210 0 : memcgid = entry & ((1UL << MEM_CGROUP_ID_SHIFT) - 1);
211 0 : entry >>= MEM_CGROUP_ID_SHIFT;
212 :
213 0 : *memcgidp = memcgid;
214 0 : *pgdat = NODE_DATA(nid);
215 0 : *evictionp = entry << bucket_order;
216 0 : *workingsetp = workingset;
217 : }
218 :
219 : /**
220 : * workingset_age_nonresident - age non-resident entries as LRU ages
221 : * @lruvec: the lruvec that was aged
222 : * @nr_pages: the number of pages to count
223 : *
224 : * As in-memory pages are aged, non-resident pages need to be aged as
225 : * well, in order for the refault distances later on to be comparable
226 : * to the in-memory dimensions. This function allows reclaim and LRU
227 : * operations to drive the non-resident aging along in parallel.
228 : */
229 0 : void workingset_age_nonresident(struct lruvec *lruvec, unsigned long nr_pages)
230 : {
231 : /*
232 : * Reclaiming a cgroup means reclaiming all its children in a
233 : * round-robin fashion. That means that each cgroup has an LRU
234 : * order that is composed of the LRU orders of its child
235 : * cgroups; and every page has an LRU position not just in the
236 : * cgroup that owns it, but in all of that group's ancestors.
237 : *
238 : * So when the physical inactive list of a leaf cgroup ages,
239 : * the virtual inactive lists of all its parents, including
240 : * the root cgroup's, age as well.
241 : */
242 : do {
243 0 : atomic_long_add(nr_pages, &lruvec->nonresident_age);
244 0 : } while ((lruvec = parent_lruvec(lruvec)));
245 0 : }
246 :
247 : /**
248 : * workingset_eviction - note the eviction of a folio from memory
249 : * @target_memcg: the cgroup that is causing the reclaim
250 : * @folio: the folio being evicted
251 : *
252 : * Return: a shadow entry to be stored in @folio->mapping->i_pages in place
253 : * of the evicted @folio so that a later refault can be detected.
254 : */
255 0 : void *workingset_eviction(struct folio *folio, struct mem_cgroup *target_memcg)
256 : {
257 0 : struct pglist_data *pgdat = folio_pgdat(folio);
258 : unsigned long eviction;
259 : struct lruvec *lruvec;
260 : int memcgid;
261 :
262 : /* Folio is fully exclusive and pins folio's memory cgroup pointer */
263 : VM_BUG_ON_FOLIO(folio_test_lru(folio), folio);
264 : VM_BUG_ON_FOLIO(folio_ref_count(folio), folio);
265 : VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
266 :
267 0 : lruvec = mem_cgroup_lruvec(target_memcg, pgdat);
268 : /* XXX: target_memcg can be NULL, go through lruvec */
269 0 : memcgid = mem_cgroup_id(lruvec_memcg(lruvec));
270 0 : eviction = atomic_long_read(&lruvec->nonresident_age);
271 0 : workingset_age_nonresident(lruvec, folio_nr_pages(folio));
272 0 : return pack_shadow(memcgid, pgdat, eviction,
273 0 : folio_test_workingset(folio));
274 : }
275 :
276 : /**
277 : * workingset_refault - Evaluate the refault of a previously evicted folio.
278 : * @folio: The freshly allocated replacement folio.
279 : * @shadow: Shadow entry of the evicted folio.
280 : *
281 : * Calculates and evaluates the refault distance of the previously
282 : * evicted folio in the context of the node and the memcg whose memory
283 : * pressure caused the eviction.
284 : */
285 0 : void workingset_refault(struct folio *folio, void *shadow)
286 : {
287 0 : bool file = folio_is_file_lru(folio);
288 : struct mem_cgroup *eviction_memcg;
289 : struct lruvec *eviction_lruvec;
290 : unsigned long refault_distance;
291 : unsigned long workingset_size;
292 : struct pglist_data *pgdat;
293 : struct mem_cgroup *memcg;
294 : unsigned long eviction;
295 : struct lruvec *lruvec;
296 : unsigned long refault;
297 : bool workingset;
298 : int memcgid;
299 : long nr;
300 :
301 0 : unpack_shadow(shadow, &memcgid, &pgdat, &eviction, &workingset);
302 :
303 : rcu_read_lock();
304 : /*
305 : * Look up the memcg associated with the stored ID. It might
306 : * have been deleted since the folio's eviction.
307 : *
308 : * Note that in rare events the ID could have been recycled
309 : * for a new cgroup that refaults a shared folio. This is
310 : * impossible to tell from the available data. However, this
311 : * should be a rare and limited disturbance, and activations
312 : * are always speculative anyway. Ultimately, it's the aging
313 : * algorithm's job to shake out the minimum access frequency
314 : * for the active cache.
315 : *
316 : * XXX: On !CONFIG_MEMCG, this will always return NULL; it
317 : * would be better if the root_mem_cgroup existed in all
318 : * configurations instead.
319 : */
320 0 : eviction_memcg = mem_cgroup_from_id(memcgid);
321 : if (!mem_cgroup_disabled() && !eviction_memcg)
322 : goto out;
323 0 : eviction_lruvec = mem_cgroup_lruvec(eviction_memcg, pgdat);
324 0 : refault = atomic_long_read(&eviction_lruvec->nonresident_age);
325 :
326 : /*
327 : * Calculate the refault distance
328 : *
329 : * The unsigned subtraction here gives an accurate distance
330 : * across nonresident_age overflows in most cases. There is a
331 : * special case: usually, shadow entries have a short lifetime
332 : * and are either refaulted or reclaimed along with the inode
333 : * before they get too old. But it is not impossible for the
334 : * nonresident_age to lap a shadow entry in the field, which
335 : * can then result in a false small refault distance, leading
336 : * to a false activation should this old entry actually
337 : * refault again. However, earlier kernels used to deactivate
338 : * unconditionally with *every* reclaim invocation for the
339 : * longest time, so the occasional inappropriate activation
340 : * leading to pressure on the active list is not a problem.
341 : */
342 0 : refault_distance = (refault - eviction) & EVICTION_MASK;
343 :
344 : /*
345 : * The activation decision for this folio is made at the level
346 : * where the eviction occurred, as that is where the LRU order
347 : * during folio reclaim is being determined.
348 : *
349 : * However, the cgroup that will own the folio is the one that
350 : * is actually experiencing the refault event.
351 : */
352 0 : nr = folio_nr_pages(folio);
353 0 : memcg = folio_memcg(folio);
354 0 : lruvec = mem_cgroup_lruvec(memcg, pgdat);
355 :
356 0 : mod_lruvec_state(lruvec, WORKINGSET_REFAULT_BASE + file, nr);
357 :
358 : mem_cgroup_flush_stats_delayed();
359 : /*
360 : * Compare the distance to the existing workingset size. We
361 : * don't activate pages that couldn't stay resident even if
362 : * all the memory was available to the workingset. Whether
363 : * workingset competition needs to consider anon or not depends
364 : * on having swap.
365 : */
366 0 : workingset_size = lruvec_page_state(eviction_lruvec, NR_ACTIVE_FILE);
367 0 : if (!file) {
368 0 : workingset_size += lruvec_page_state(eviction_lruvec,
369 : NR_INACTIVE_FILE);
370 : }
371 0 : if (mem_cgroup_get_nr_swap_pages(memcg) > 0) {
372 0 : workingset_size += lruvec_page_state(eviction_lruvec,
373 : NR_ACTIVE_ANON);
374 0 : if (file) {
375 0 : workingset_size += lruvec_page_state(eviction_lruvec,
376 : NR_INACTIVE_ANON);
377 : }
378 : }
379 0 : if (refault_distance > workingset_size)
380 : goto out;
381 :
382 0 : folio_set_active(folio);
383 0 : workingset_age_nonresident(lruvec, nr);
384 0 : mod_lruvec_state(lruvec, WORKINGSET_ACTIVATE_BASE + file, nr);
385 :
386 : /* Folio was active prior to eviction */
387 0 : if (workingset) {
388 0 : folio_set_workingset(folio);
389 : /* XXX: Move to lru_cache_add() when it supports new vs putback */
390 0 : lru_note_cost_folio(folio);
391 0 : mod_lruvec_state(lruvec, WORKINGSET_RESTORE_BASE + file, nr);
392 : }
393 : out:
394 : rcu_read_unlock();
395 0 : }
396 :
397 : /**
398 : * workingset_activation - note a page activation
399 : * @folio: Folio that is being activated.
400 : */
401 0 : void workingset_activation(struct folio *folio)
402 : {
403 : struct mem_cgroup *memcg;
404 :
405 : rcu_read_lock();
406 : /*
407 : * Filter non-memcg pages here, e.g. unmap can call
408 : * mark_page_accessed() on VDSO pages.
409 : *
410 : * XXX: See workingset_refault() - this should return
411 : * root_mem_cgroup even for !CONFIG_MEMCG.
412 : */
413 0 : memcg = folio_memcg_rcu(folio);
414 : if (!mem_cgroup_disabled() && !memcg)
415 : goto out;
416 0 : workingset_age_nonresident(folio_lruvec(folio), folio_nr_pages(folio));
417 : out:
418 : rcu_read_unlock();
419 0 : }
420 :
421 : /*
422 : * Shadow entries reflect the share of the working set that does not
423 : * fit into memory, so their number depends on the access pattern of
424 : * the workload. In most cases, they will refault or get reclaimed
425 : * along with the inode, but a (malicious) workload that streams
426 : * through files with a total size several times that of available
427 : * memory, while preventing the inodes from being reclaimed, can
428 : * create excessive amounts of shadow nodes. To keep a lid on this,
429 : * track shadow nodes and reclaim them when they grow way past the
430 : * point where they would still be useful.
431 : */
432 :
433 : struct list_lru shadow_nodes;
434 :
435 0 : void workingset_update_node(struct xa_node *node)
436 : {
437 : struct address_space *mapping;
438 :
439 : /*
440 : * Track non-empty nodes that contain only shadow entries;
441 : * unlink those that contain pages or are being freed.
442 : *
443 : * Avoid acquiring the list_lru lock when the nodes are
444 : * already where they should be. The list_empty() test is safe
445 : * as node->private_list is protected by the i_pages lock.
446 : */
447 0 : mapping = container_of(node->array, struct address_space, i_pages);
448 : lockdep_assert_held(&mapping->i_pages.xa_lock);
449 :
450 0 : if (node->count && node->count == node->nr_values) {
451 0 : if (list_empty(&node->private_list)) {
452 0 : list_lru_add(&shadow_nodes, &node->private_list);
453 : __inc_lruvec_kmem_state(node, WORKINGSET_NODES);
454 : }
455 : } else {
456 0 : if (!list_empty(&node->private_list)) {
457 0 : list_lru_del(&shadow_nodes, &node->private_list);
458 : __dec_lruvec_kmem_state(node, WORKINGSET_NODES);
459 : }
460 : }
461 0 : }
462 :
463 0 : static unsigned long count_shadow_nodes(struct shrinker *shrinker,
464 : struct shrink_control *sc)
465 : {
466 : unsigned long max_nodes;
467 : unsigned long nodes;
468 : unsigned long pages;
469 :
470 0 : nodes = list_lru_shrink_count(&shadow_nodes, sc);
471 0 : if (!nodes)
472 : return SHRINK_EMPTY;
473 :
474 : /*
475 : * Approximate a reasonable limit for the nodes
476 : * containing shadow entries. We don't need to keep more
477 : * shadow entries than possible pages on the active list,
478 : * since refault distances bigger than that are dismissed.
479 : *
480 : * The size of the active list converges toward 100% of
481 : * overall page cache as memory grows, with only a tiny
482 : * inactive list. Assume the total cache size for that.
483 : *
484 : * Nodes might be sparsely populated, with only one shadow
485 : * entry in the extreme case. Obviously, we cannot keep one
486 : * node for every eligible shadow entry, so compromise on a
487 : * worst-case density of 1/8th. Below that, not all eligible
488 : * refaults can be detected anymore.
489 : *
490 : * On 64-bit with 7 xa_nodes per page and 64 slots
491 : * each, this will reclaim shadow entries when they consume
492 : * ~1.8% of available memory:
493 : *
494 : * PAGE_SIZE / xa_nodes / node_entries * 8 / PAGE_SIZE
495 : */
496 : #ifdef CONFIG_MEMCG
497 : if (sc->memcg) {
498 : struct lruvec *lruvec;
499 : int i;
500 :
501 : lruvec = mem_cgroup_lruvec(sc->memcg, NODE_DATA(sc->nid));
502 : for (pages = 0, i = 0; i < NR_LRU_LISTS; i++)
503 : pages += lruvec_page_state_local(lruvec,
504 : NR_LRU_BASE + i);
505 : pages += lruvec_page_state_local(
506 : lruvec, NR_SLAB_RECLAIMABLE_B) >> PAGE_SHIFT;
507 : pages += lruvec_page_state_local(
508 : lruvec, NR_SLAB_UNRECLAIMABLE_B) >> PAGE_SHIFT;
509 : } else
510 : #endif
511 0 : pages = node_present_pages(sc->nid);
512 :
513 0 : max_nodes = pages >> (XA_CHUNK_SHIFT - 3);
514 :
515 0 : if (nodes <= max_nodes)
516 : return 0;
517 0 : return nodes - max_nodes;
518 : }
519 :
520 0 : static enum lru_status shadow_lru_isolate(struct list_head *item,
521 : struct list_lru_one *lru,
522 : spinlock_t *lru_lock,
523 : void *arg) __must_hold(lru_lock)
524 : {
525 0 : struct xa_node *node = container_of(item, struct xa_node, private_list);
526 : struct address_space *mapping;
527 : int ret;
528 :
529 : /*
530 : * Page cache insertions and deletions synchronously maintain
531 : * the shadow node LRU under the i_pages lock and the
532 : * lru_lock. Because the page cache tree is emptied before
533 : * the inode can be destroyed, holding the lru_lock pins any
534 : * address_space that has nodes on the LRU.
535 : *
536 : * We can then safely transition to the i_pages lock to
537 : * pin only the address_space of the particular node we want
538 : * to reclaim, take the node off-LRU, and drop the lru_lock.
539 : */
540 :
541 0 : mapping = container_of(node->array, struct address_space, i_pages);
542 :
543 : /* Coming from the list, invert the lock order */
544 0 : if (!xa_trylock(&mapping->i_pages)) {
545 : spin_unlock_irq(lru_lock);
546 : ret = LRU_RETRY;
547 : goto out;
548 : }
549 :
550 0 : if (!spin_trylock(&mapping->host->i_lock)) {
551 : xa_unlock(&mapping->i_pages);
552 : spin_unlock_irq(lru_lock);
553 : ret = LRU_RETRY;
554 : goto out;
555 : }
556 :
557 0 : list_lru_isolate(lru, item);
558 0 : __dec_lruvec_kmem_state(node, WORKINGSET_NODES);
559 :
560 0 : spin_unlock(lru_lock);
561 :
562 : /*
563 : * The nodes should only contain one or more shadow entries,
564 : * no pages, so we expect to be able to remove them all and
565 : * delete and free the empty node afterwards.
566 : */
567 0 : if (WARN_ON_ONCE(!node->nr_values))
568 : goto out_invalid;
569 0 : if (WARN_ON_ONCE(node->count != node->nr_values))
570 : goto out_invalid;
571 0 : xa_delete_node(node, workingset_update_node);
572 : __inc_lruvec_kmem_state(node, WORKINGSET_NODERECLAIM);
573 :
574 : out_invalid:
575 0 : xa_unlock_irq(&mapping->i_pages);
576 0 : if (mapping_shrinkable(mapping))
577 0 : inode_add_lru(mapping->host);
578 0 : spin_unlock(&mapping->host->i_lock);
579 0 : ret = LRU_REMOVED_RETRY;
580 : out:
581 0 : cond_resched();
582 0 : spin_lock_irq(lru_lock);
583 0 : return ret;
584 : }
585 :
586 0 : static unsigned long scan_shadow_nodes(struct shrinker *shrinker,
587 : struct shrink_control *sc)
588 : {
589 : /* list_lru lock nests inside the IRQ-safe i_pages lock */
590 0 : return list_lru_shrink_walk_irq(&shadow_nodes, sc, shadow_lru_isolate,
591 : NULL);
592 : }
593 :
594 : static struct shrinker workingset_shadow_shrinker = {
595 : .count_objects = count_shadow_nodes,
596 : .scan_objects = scan_shadow_nodes,
597 : .seeks = 0, /* ->count reports only fully expendable nodes */
598 : .flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE,
599 : };
600 :
601 : /*
602 : * Our list_lru->lock is IRQ-safe as it nests inside the IRQ-safe
603 : * i_pages lock.
604 : */
605 : static struct lock_class_key shadow_nodes_key;
606 :
607 1 : static int __init workingset_init(void)
608 : {
609 : unsigned int timestamp_bits;
610 : unsigned int max_order;
611 : int ret;
612 :
613 : BUILD_BUG_ON(BITS_PER_LONG < EVICTION_SHIFT);
614 : /*
615 : * Calculate the eviction bucket size to cover the longest
616 : * actionable refault distance, which is currently half of
617 : * memory (totalram_pages/2). However, memory hotplug may add
618 : * some more pages at runtime, so keep working with up to
619 : * double the initial memory by using totalram_pages as-is.
620 : */
621 1 : timestamp_bits = BITS_PER_LONG - EVICTION_SHIFT;
622 2 : max_order = fls_long(totalram_pages() - 1);
623 1 : if (max_order > timestamp_bits)
624 0 : bucket_order = max_order - timestamp_bits;
625 1 : pr_info("workingset: timestamp_bits=%d max_order=%d bucket_order=%u\n",
626 : timestamp_bits, max_order, bucket_order);
627 :
628 1 : ret = prealloc_shrinker(&workingset_shadow_shrinker);
629 1 : if (ret)
630 : goto err;
631 1 : ret = __list_lru_init(&shadow_nodes, true, &shadow_nodes_key,
632 : &workingset_shadow_shrinker);
633 1 : if (ret)
634 : goto err_list_lru;
635 1 : register_shrinker_prepared(&workingset_shadow_shrinker);
636 1 : return 0;
637 : err_list_lru:
638 0 : free_prealloced_shrinker(&workingset_shadow_shrinker);
639 : err:
640 : return ret;
641 : }
642 : module_init(workingset_init);
|
