1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Workingset detection
4  *
5  * Copyright (C) 2013 Red Hat, Inc., Johannes Weiner
6  */
7 
8 #include <linux/memcontrol.h>
9 #include <linux/mm_inline.h>
10 #include <linux/writeback.h>
11 #include <linux/shmem_fs.h>
12 #include <linux/pagemap.h>
13 #include <linux/atomic.h>
14 #include <linux/module.h>
15 #include <linux/swap.h>
16 #include <linux/dax.h>
17 #include <linux/fs.h>
18 #include <linux/mm.h>
19 
20 /*
21  *		Double CLOCK lists
22  *
23  * Per node, two clock lists are maintained for file pages: the
24  * inactive and the active list.  Freshly faulted pages start out at
25  * the head of the inactive list and page reclaim scans pages from the
26  * tail.  Pages that are accessed multiple times on the inactive list
27  * are promoted to the active list, to protect them from reclaim,
28  * whereas active pages are demoted to the inactive list when the
29  * active list grows too big.
30  *
31  *   fault ------------------------+
32  *                                 |
33  *              +--------------+   |            +-------------+
34  *   reclaim <- |   inactive   | <-+-- demotion |    active   | <--+
35  *              +--------------+                +-------------+    |
36  *                     |                                           |
37  *                     +-------------- promotion ------------------+
38  *
39  *
40  *		Access frequency and refault distance
41  *
42  * A workload is thrashing when its pages are frequently used but they
43  * are evicted from the inactive list every time before another access
44  * would have promoted them to the active list.
45  *
46  * In cases where the average access distance between thrashing pages
47  * is bigger than the size of memory there is nothing that can be
48  * done - the thrashing set could never fit into memory under any
49  * circumstance.
50  *
51  * However, the average access distance could be bigger than the
52  * inactive list, yet smaller than the size of memory.  In this case,
53  * the set could fit into memory if it weren't for the currently
54  * active pages - which may be used more, hopefully less frequently:
55  *
56  *      +-memory available to cache-+
57  *      |                           |
58  *      +-inactive------+-active----+
59  *  a b | c d e f g h i | J K L M N |
60  *      +---------------+-----------+
61  *
62  * It is prohibitively expensive to accurately track access frequency
63  * of pages.  But a reasonable approximation can be made to measure
64  * thrashing on the inactive list, after which refaulting pages can be
65  * activated optimistically to compete with the existing active pages.
66  *
67  * Approximating inactive page access frequency - Observations:
68  *
69  * 1. When a page is accessed for the first time, it is added to the
70  *    head of the inactive list, slides every existing inactive page
71  *    towards the tail by one slot, and pushes the current tail page
72  *    out of memory.
73  *
74  * 2. When a page is accessed for the second time, it is promoted to
75  *    the active list, shrinking the inactive list by one slot.  This
76  *    also slides all inactive pages that were faulted into the cache
77  *    more recently than the activated page towards the tail of the
78  *    inactive list.
79  *
80  * Thus:
81  *
82  * 1. The sum of evictions and activations between any two points in
83  *    time indicate the minimum number of inactive pages accessed in
84  *    between.
85  *
86  * 2. Moving one inactive page N page slots towards the tail of the
87  *    list requires at least N inactive page accesses.
88  *
89  * Combining these:
90  *
91  * 1. When a page is finally evicted from memory, the number of
92  *    inactive pages accessed while the page was in cache is at least
93  *    the number of page slots on the inactive list.
94  *
95  * 2. In addition, measuring the sum of evictions and activations (E)
96  *    at the time of a page's eviction, and comparing it to another
97  *    reading (R) at the time the page faults back into memory tells
98  *    the minimum number of accesses while the page was not cached.
99  *    This is called the refault distance.
100  *
101  * Because the first access of the page was the fault and the second
102  * access the refault, we combine the in-cache distance with the
103  * out-of-cache distance to get the complete minimum access distance
104  * of this page:
105  *
106  *      NR_inactive + (R - E)
107  *
108  * And knowing the minimum access distance of a page, we can easily
109  * tell if the page would be able to stay in cache assuming all page
110  * slots in the cache were available:
111  *
112  *   NR_inactive + (R - E) <= NR_inactive + NR_active
113  *
114  * which can be further simplified to
115  *
116  *   (R - E) <= NR_active
117  *
118  * Put into words, the refault distance (out-of-cache) can be seen as
119  * a deficit in inactive list space (in-cache).  If the inactive list
120  * had (R - E) more page slots, the page would not have been evicted
121  * in between accesses, but activated instead.  And on a full system,
122  * the only thing eating into inactive list space is active pages.
123  *
124  *
125  *		Refaulting inactive pages
126  *
127  * All that is known about the active list is that the pages have been
128  * accessed more than once in the past.  This means that at any given
129  * time there is actually a good chance that pages on the active list
130  * are no longer in active use.
131  *
132  * So when a refault distance of (R - E) is observed and there are at
133  * least (R - E) active pages, the refaulting page is activated
134  * optimistically in the hope that (R - E) active pages are actually
135  * used less frequently than the refaulting page - or even not used at
136  * all anymore.
137  *
138  * That means if inactive cache is refaulting with a suitable refault
139  * distance, we assume the cache workingset is transitioning and put
140  * pressure on the current active list.
141  *
142  * If this is wrong and demotion kicks in, the pages which are truly
143  * used more frequently will be reactivated while the less frequently
144  * used once will be evicted from memory.
145  *
146  * But if this is right, the stale pages will be pushed out of memory
147  * and the used pages get to stay in cache.
148  *
149  *		Refaulting active pages
150  *
151  * If on the other hand the refaulting pages have recently been
152  * deactivated, it means that the active list is no longer protecting
153  * actively used cache from reclaim. The cache is NOT transitioning to
154  * a different workingset; the existing workingset is thrashing in the
155  * space allocated to the page cache.
156  *
157  *
158  *		Implementation
159  *
160  * For each node's LRU lists, a counter for inactive evictions and
161  * activations is maintained (node->nonresident_age).
162  *
163  * On eviction, a snapshot of this counter (along with some bits to
164  * identify the node) is stored in the now empty page cache
165  * slot of the evicted page.  This is called a shadow entry.
166  *
167  * On cache misses for which there are shadow entries, an eligible
168  * refault distance will immediately activate the refaulting page.
169  */
170 
171 #define WORKINGSET_SHIFT 1
172 #define EVICTION_SHIFT	((BITS_PER_LONG - BITS_PER_XA_VALUE) +	\
173 			 WORKINGSET_SHIFT + NODES_SHIFT + \
174 			 MEM_CGROUP_ID_SHIFT)
175 #define EVICTION_MASK	(~0UL >> EVICTION_SHIFT)
176 
177 /*
178  * Eviction timestamps need to be able to cover the full range of
179  * actionable refaults. However, bits are tight in the xarray
180  * entry, and after storing the identifier for the lruvec there might
181  * not be enough left to represent every single actionable refault. In
182  * that case, we have to sacrifice granularity for distance, and group
183  * evictions into coarser buckets by shaving off lower timestamp bits.
184  */
185 static unsigned int bucket_order __read_mostly;
186 
pack_shadow(int memcgid,pg_data_t * pgdat,unsigned long eviction,bool workingset)187 static void *pack_shadow(int memcgid, pg_data_t *pgdat, unsigned long eviction,
188 			 bool workingset)
189 {
190 	eviction >>= bucket_order;
191 	eviction &= EVICTION_MASK;
192 	eviction = (eviction << MEM_CGROUP_ID_SHIFT) | memcgid;
193 	eviction = (eviction << NODES_SHIFT) | pgdat->node_id;
194 	eviction = (eviction << WORKINGSET_SHIFT) | workingset;
195 
196 	return xa_mk_value(eviction);
197 }
198 
unpack_shadow(void * shadow,int * memcgidp,pg_data_t ** pgdat,unsigned long * evictionp,bool * workingsetp)199 static void unpack_shadow(void *shadow, int *memcgidp, pg_data_t **pgdat,
200 			  unsigned long *evictionp, bool *workingsetp)
201 {
202 	unsigned long entry = xa_to_value(shadow);
203 	int memcgid, nid;
204 	bool workingset;
205 
206 	workingset = entry & ((1UL << WORKINGSET_SHIFT) - 1);
207 	entry >>= WORKINGSET_SHIFT;
208 	nid = entry & ((1UL << NODES_SHIFT) - 1);
209 	entry >>= NODES_SHIFT;
210 	memcgid = entry & ((1UL << MEM_CGROUP_ID_SHIFT) - 1);
211 	entry >>= MEM_CGROUP_ID_SHIFT;
212 
213 	*memcgidp = memcgid;
214 	*pgdat = NODE_DATA(nid);
215 	*evictionp = entry << bucket_order;
216 	*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  */
workingset_age_nonresident(struct lruvec * lruvec,unsigned long nr_pages)229 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 		atomic_long_add(nr_pages, &lruvec->nonresident_age);
244 	} while ((lruvec = parent_lruvec(lruvec)));
245 }
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  */
workingset_eviction(struct folio * folio,struct mem_cgroup * target_memcg)255 void *workingset_eviction(struct folio *folio, struct mem_cgroup *target_memcg)
256 {
257 	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 	lruvec = mem_cgroup_lruvec(target_memcg, pgdat);
268 	/* XXX: target_memcg can be NULL, go through lruvec */
269 	memcgid = mem_cgroup_id(lruvec_memcg(lruvec));
270 	eviction = atomic_long_read(&lruvec->nonresident_age);
271 	workingset_age_nonresident(lruvec, folio_nr_pages(folio));
272 	return pack_shadow(memcgid, pgdat, eviction,
273 				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  */
workingset_refault(struct folio * folio,void * shadow)285 void workingset_refault(struct folio *folio, void *shadow)
286 {
287 	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 	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 	eviction_memcg = mem_cgroup_from_id(memcgid);
321 	if (!mem_cgroup_disabled() && !eviction_memcg)
322 		goto out;
323 	eviction_lruvec = mem_cgroup_lruvec(eviction_memcg, pgdat);
324 	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 	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 	nr = folio_nr_pages(folio);
353 	memcg = folio_memcg(folio);
354 	lruvec = mem_cgroup_lruvec(memcg, pgdat);
355 
356 	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 	workingset_size = lruvec_page_state(eviction_lruvec, NR_ACTIVE_FILE);
367 	if (!file) {
368 		workingset_size += lruvec_page_state(eviction_lruvec,
369 						     NR_INACTIVE_FILE);
370 	}
371 	if (mem_cgroup_get_nr_swap_pages(memcg) > 0) {
372 		workingset_size += lruvec_page_state(eviction_lruvec,
373 						     NR_ACTIVE_ANON);
374 		if (file) {
375 			workingset_size += lruvec_page_state(eviction_lruvec,
376 						     NR_INACTIVE_ANON);
377 		}
378 	}
379 	if (refault_distance > workingset_size)
380 		goto out;
381 
382 	folio_set_active(folio);
383 	workingset_age_nonresident(lruvec, nr);
384 	mod_lruvec_state(lruvec, WORKINGSET_ACTIVATE_BASE + file, nr);
385 
386 	/* Folio was active prior to eviction */
387 	if (workingset) {
388 		folio_set_workingset(folio);
389 		/* XXX: Move to lru_cache_add() when it supports new vs putback */
390 		lru_note_cost_folio(folio);
391 		mod_lruvec_state(lruvec, WORKINGSET_RESTORE_BASE + file, nr);
392 	}
393 out:
394 	rcu_read_unlock();
395 }
396 
397 /**
398  * workingset_activation - note a page activation
399  * @folio: Folio that is being activated.
400  */
workingset_activation(struct folio * folio)401 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 	memcg = folio_memcg_rcu(folio);
414 	if (!mem_cgroup_disabled() && !memcg)
415 		goto out;
416 	workingset_age_nonresident(folio_lruvec(folio), folio_nr_pages(folio));
417 out:
418 	rcu_read_unlock();
419 }
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 
workingset_update_node(struct xa_node * node)435 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 	mapping = container_of(node->array, struct address_space, i_pages);
448 	lockdep_assert_held(&mapping->i_pages.xa_lock);
449 
450 	if (node->count && node->count == node->nr_values) {
451 		if (list_empty(&node->private_list)) {
452 			list_lru_add(&shadow_nodes, &node->private_list);
453 			__inc_lruvec_kmem_state(node, WORKINGSET_NODES);
454 		}
455 	} else {
456 		if (!list_empty(&node->private_list)) {
457 			list_lru_del(&shadow_nodes, &node->private_list);
458 			__dec_lruvec_kmem_state(node, WORKINGSET_NODES);
459 		}
460 	}
461 }
462 
count_shadow_nodes(struct shrinker * shrinker,struct shrink_control * sc)463 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 	nodes = list_lru_shrink_count(&shadow_nodes, sc);
471 	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 		pages = node_present_pages(sc->nid);
512 
513 	max_nodes = pages >> (XA_CHUNK_SHIFT - 3);
514 
515 	if (nodes <= max_nodes)
516 		return 0;
517 	return nodes - max_nodes;
518 }
519 
shadow_lru_isolate(struct list_head * item,struct list_lru_one * lru,spinlock_t * lru_lock,void * arg)520 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 	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 	mapping = container_of(node->array, struct address_space, i_pages);
542 
543 	/* Coming from the list, invert the lock order */
544 	if (!xa_trylock(&mapping->i_pages)) {
545 		spin_unlock_irq(lru_lock);
546 		ret = LRU_RETRY;
547 		goto out;
548 	}
549 
550 	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 	list_lru_isolate(lru, item);
558 	__dec_lruvec_kmem_state(node, WORKINGSET_NODES);
559 
560 	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 	if (WARN_ON_ONCE(!node->nr_values))
568 		goto out_invalid;
569 	if (WARN_ON_ONCE(node->count != node->nr_values))
570 		goto out_invalid;
571 	xa_delete_node(node, workingset_update_node);
572 	__inc_lruvec_kmem_state(node, WORKINGSET_NODERECLAIM);
573 
574 out_invalid:
575 	xa_unlock_irq(&mapping->i_pages);
576 	if (mapping_shrinkable(mapping))
577 		inode_add_lru(mapping->host);
578 	spin_unlock(&mapping->host->i_lock);
579 	ret = LRU_REMOVED_RETRY;
580 out:
581 	cond_resched();
582 	spin_lock_irq(lru_lock);
583 	return ret;
584 }
585 
scan_shadow_nodes(struct shrinker * shrinker,struct shrink_control * sc)586 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 	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 
workingset_init(void)607 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 	timestamp_bits = BITS_PER_LONG - EVICTION_SHIFT;
622 	max_order = fls_long(totalram_pages() - 1);
623 	if (max_order > timestamp_bits)
624 		bucket_order = max_order - timestamp_bits;
625 	pr_info("workingset: timestamp_bits=%d max_order=%d bucket_order=%u\n",
626 	       timestamp_bits, max_order, bucket_order);
627 
628 	ret = prealloc_shrinker(&workingset_shadow_shrinker);
629 	if (ret)
630 		goto err;
631 	ret = __list_lru_init(&shadow_nodes, true, &shadow_nodes_key,
632 			      &workingset_shadow_shrinker);
633 	if (ret)
634 		goto err_list_lru;
635 	register_shrinker_prepared(&workingset_shadow_shrinker);
636 	return 0;
637 err_list_lru:
638 	free_prealloced_shrinker(&workingset_shadow_shrinker);
639 err:
640 	return ret;
641 }
642 module_init(workingset_init);
643