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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/writeback.h>
10 : : #include <linux/shmem_fs.h>
11 : : #include <linux/pagemap.h>
12 : : #include <linux/atomic.h>
13 : : #include <linux/module.h>
14 : : #include <linux/swap.h>
15 : : #include <linux/dax.h>
16 : : #include <linux/fs.h>
17 : : #include <linux/mm.h>
18 : :
19 : : /*
20 : : * Double CLOCK lists
21 : : *
22 : : * Per node, two clock lists are maintained for file pages: the
23 : : * inactive and the active list. Freshly faulted pages start out at
24 : : * the head of the inactive list and page reclaim scans pages from the
25 : : * tail. Pages that are accessed multiple times on the inactive list
26 : : * are promoted to the active list, to protect them from reclaim,
27 : : * whereas active pages are demoted to the inactive list when the
28 : : * active list grows too big.
29 : : *
30 : : * fault ------------------------+
31 : : * |
32 : : * +--------------+ | +-------------+
33 : : * reclaim <- | inactive | <-+-- demotion | active | <--+
34 : : * +--------------+ +-------------+ |
35 : : * | |
36 : : * +-------------- promotion ------------------+
37 : : *
38 : : *
39 : : * Access frequency and refault distance
40 : : *
41 : : * A workload is thrashing when its pages are frequently used but they
42 : : * are evicted from the inactive list every time before another access
43 : : * would have promoted them to the active list.
44 : : *
45 : : * In cases where the average access distance between thrashing pages
46 : : * is bigger than the size of memory there is nothing that can be
47 : : * done - the thrashing set could never fit into memory under any
48 : : * circumstance.
49 : : *
50 : : * However, the average access distance could be bigger than the
51 : : * inactive list, yet smaller than the size of memory. In this case,
52 : : * the set could fit into memory if it weren't for the currently
53 : : * active pages - which may be used more, hopefully less frequently:
54 : : *
55 : : * +-memory available to cache-+
56 : : * | |
57 : : * +-inactive------+-active----+
58 : : * a b | c d e f g h i | J K L M N |
59 : : * +---------------+-----------+
60 : : *
61 : : * It is prohibitively expensive to accurately track access frequency
62 : : * of pages. But a reasonable approximation can be made to measure
63 : : * thrashing on the inactive list, after which refaulting pages can be
64 : : * activated optimistically to compete with the existing active pages.
65 : : *
66 : : * Approximating inactive page access frequency - Observations:
67 : : *
68 : : * 1. When a page is accessed for the first time, it is added to the
69 : : * head of the inactive list, slides every existing inactive page
70 : : * towards the tail by one slot, and pushes the current tail page
71 : : * out of memory.
72 : : *
73 : : * 2. When a page is accessed for the second time, it is promoted to
74 : : * the active list, shrinking the inactive list by one slot. This
75 : : * also slides all inactive pages that were faulted into the cache
76 : : * more recently than the activated page towards the tail of the
77 : : * inactive list.
78 : : *
79 : : * Thus:
80 : : *
81 : : * 1. The sum of evictions and activations between any two points in
82 : : * time indicate the minimum number of inactive pages accessed in
83 : : * between.
84 : : *
85 : : * 2. Moving one inactive page N page slots towards the tail of the
86 : : * list requires at least N inactive page accesses.
87 : : *
88 : : * Combining these:
89 : : *
90 : : * 1. When a page is finally evicted from memory, the number of
91 : : * inactive pages accessed while the page was in cache is at least
92 : : * the number of page slots on the inactive list.
93 : : *
94 : : * 2. In addition, measuring the sum of evictions and activations (E)
95 : : * at the time of a page's eviction, and comparing it to another
96 : : * reading (R) at the time the page faults back into memory tells
97 : : * the minimum number of accesses while the page was not cached.
98 : : * This is called the refault distance.
99 : : *
100 : : * Because the first access of the page was the fault and the second
101 : : * access the refault, we combine the in-cache distance with the
102 : : * out-of-cache distance to get the complete minimum access distance
103 : : * of this page:
104 : : *
105 : : * NR_inactive + (R - E)
106 : : *
107 : : * And knowing the minimum access distance of a page, we can easily
108 : : * tell if the page would be able to stay in cache assuming all page
109 : : * slots in the cache were available:
110 : : *
111 : : * NR_inactive + (R - E) <= NR_inactive + NR_active
112 : : *
113 : : * which can be further simplified to
114 : : *
115 : : * (R - E) <= NR_active
116 : : *
117 : : * Put into words, the refault distance (out-of-cache) can be seen as
118 : : * a deficit in inactive list space (in-cache). If the inactive list
119 : : * had (R - E) more page slots, the page would not have been evicted
120 : : * in between accesses, but activated instead. And on a full system,
121 : : * the only thing eating into inactive list space is active pages.
122 : : *
123 : : *
124 : : * Refaulting inactive pages
125 : : *
126 : : * All that is known about the active list is that the pages have been
127 : : * accessed more than once in the past. This means that at any given
128 : : * time there is actually a good chance that pages on the active list
129 : : * are no longer in active use.
130 : : *
131 : : * So when a refault distance of (R - E) is observed and there are at
132 : : * least (R - E) active pages, the refaulting page is activated
133 : : * optimistically in the hope that (R - E) active pages are actually
134 : : * used less frequently than the refaulting page - or even not used at
135 : : * all anymore.
136 : : *
137 : : * That means if inactive cache is refaulting with a suitable refault
138 : : * distance, we assume the cache workingset is transitioning and put
139 : : * pressure on the current active list.
140 : : *
141 : : * If this is wrong and demotion kicks in, the pages which are truly
142 : : * used more frequently will be reactivated while the less frequently
143 : : * used once will be evicted from memory.
144 : : *
145 : : * But if this is right, the stale pages will be pushed out of memory
146 : : * and the used pages get to stay in cache.
147 : : *
148 : : * Refaulting active pages
149 : : *
150 : : * If on the other hand the refaulting pages have recently been
151 : : * deactivated, it means that the active list is no longer protecting
152 : : * actively used cache from reclaim. The cache is NOT transitioning to
153 : : * a different workingset; the existing workingset is thrashing in the
154 : : * space allocated to the page cache.
155 : : *
156 : : *
157 : : * Implementation
158 : : *
159 : : * For each node's file LRU lists, a counter for inactive evictions
160 : : * and activations is maintained (node->inactive_age).
161 : : *
162 : : * On eviction, a snapshot of this counter (along with some bits to
163 : : * identify the node) is stored in the now empty page cache
164 : : * slot of the evicted page. This is called a shadow entry.
165 : : *
166 : : * On cache misses for which there are shadow entries, an eligible
167 : : * refault distance will immediately activate the refaulting page.
168 : : */
169 : :
170 : : #define EVICTION_SHIFT ((BITS_PER_LONG - BITS_PER_XA_VALUE) + \
171 : : 1 + NODES_SHIFT + MEM_CGROUP_ID_SHIFT)
172 : : #define EVICTION_MASK (~0UL >> EVICTION_SHIFT)
173 : :
174 : : /*
175 : : * Eviction timestamps need to be able to cover the full range of
176 : : * actionable refaults. However, bits are tight in the xarray
177 : : * entry, and after storing the identifier for the lruvec there might
178 : : * not be enough left to represent every single actionable refault. In
179 : : * that case, we have to sacrifice granularity for distance, and group
180 : : * evictions into coarser buckets by shaving off lower timestamp bits.
181 : : */
182 : : static unsigned int bucket_order __read_mostly;
183 : :
184 : 0 : static void *pack_shadow(int memcgid, pg_data_t *pgdat, unsigned long eviction,
185 : : bool workingset)
186 : : {
187 : 0 : eviction >>= bucket_order;
188 : 0 : eviction &= EVICTION_MASK;
189 : 0 : eviction = (eviction << MEM_CGROUP_ID_SHIFT) | memcgid;
190 : 0 : eviction = (eviction << NODES_SHIFT) | pgdat->node_id;
191 : 0 : eviction = (eviction << 1) | workingset;
192 : :
193 [ # # ]: 0 : return xa_mk_value(eviction);
194 : : }
195 : :
196 : 0 : static void unpack_shadow(void *shadow, int *memcgidp, pg_data_t **pgdat,
197 : : unsigned long *evictionp, bool *workingsetp)
198 : : {
199 : 0 : unsigned long entry = xa_to_value(shadow);
200 : 0 : int memcgid, nid;
201 : 0 : bool workingset;
202 : :
203 : 0 : workingset = entry & 1;
204 : 0 : entry >>= 1;
205 : 0 : nid = entry & ((1UL << NODES_SHIFT) - 1);
206 : 0 : entry >>= NODES_SHIFT;
207 : 0 : memcgid = entry & ((1UL << MEM_CGROUP_ID_SHIFT) - 1);
208 : 0 : entry >>= MEM_CGROUP_ID_SHIFT;
209 : :
210 : 0 : *memcgidp = memcgid;
211 : 0 : *pgdat = NODE_DATA(nid);
212 : 0 : *evictionp = entry << bucket_order;
213 : 0 : *workingsetp = workingset;
214 : : }
215 : :
216 : 96430 : static void advance_inactive_age(struct mem_cgroup *memcg, pg_data_t *pgdat)
217 : : {
218 : : /*
219 : : * Reclaiming a cgroup means reclaiming all its children in a
220 : : * round-robin fashion. That means that each cgroup has an LRU
221 : : * order that is composed of the LRU orders of its child
222 : : * cgroups; and every page has an LRU position not just in the
223 : : * cgroup that owns it, but in all of that group's ancestors.
224 : : *
225 : : * So when the physical inactive list of a leaf cgroup ages,
226 : : * the virtual inactive lists of all its parents, including
227 : : * the root cgroup's, age as well.
228 : : */
229 : 96430 : do {
230 : 96430 : struct lruvec *lruvec;
231 : :
232 : 96430 : lruvec = mem_cgroup_lruvec(memcg, pgdat);
233 : 96430 : atomic_long_inc(&lruvec->inactive_age);
234 : 96430 : } while (memcg && (memcg = parent_mem_cgroup(memcg)));
235 : : }
236 : :
237 : : /**
238 : : * workingset_eviction - note the eviction of a page from memory
239 : : * @target_memcg: the cgroup that is causing the reclaim
240 : : * @page: the page being evicted
241 : : *
242 : : * Returns a shadow entry to be stored in @page->mapping->i_pages in place
243 : : * of the evicted @page so that a later refault can be detected.
244 : : */
245 : 0 : void *workingset_eviction(struct page *page, struct mem_cgroup *target_memcg)
246 : : {
247 : 0 : struct pglist_data *pgdat = page_pgdat(page);
248 : 0 : unsigned long eviction;
249 : 0 : struct lruvec *lruvec;
250 : 0 : int memcgid;
251 : :
252 : : /* Page is fully exclusive and pins page->mem_cgroup */
253 : 0 : VM_BUG_ON_PAGE(PageLRU(page), page);
254 : 0 : VM_BUG_ON_PAGE(page_count(page), page);
255 : 0 : VM_BUG_ON_PAGE(!PageLocked(page), page);
256 : :
257 : 0 : advance_inactive_age(page_memcg(page), pgdat);
258 : :
259 : 0 : lruvec = mem_cgroup_lruvec(target_memcg, pgdat);
260 : : /* XXX: target_memcg can be NULL, go through lruvec */
261 : 0 : memcgid = mem_cgroup_id(lruvec_memcg(lruvec));
262 : 0 : eviction = atomic_long_read(&lruvec->inactive_age);
263 [ # # ]: 0 : return pack_shadow(memcgid, pgdat, eviction, PageWorkingset(page));
264 : : }
265 : :
266 : : /**
267 : : * workingset_refault - evaluate the refault of a previously evicted page
268 : : * @page: the freshly allocated replacement page
269 : : * @shadow: shadow entry of the evicted page
270 : : *
271 : : * Calculates and evaluates the refault distance of the previously
272 : : * evicted page in the context of the node and the memcg whose memory
273 : : * pressure caused the eviction.
274 : : */
275 : 0 : void workingset_refault(struct page *page, void *shadow)
276 : : {
277 : 0 : struct mem_cgroup *eviction_memcg;
278 : 0 : struct lruvec *eviction_lruvec;
279 : 0 : unsigned long refault_distance;
280 : 0 : struct pglist_data *pgdat;
281 : 0 : unsigned long active_file;
282 : 0 : struct mem_cgroup *memcg;
283 : 0 : unsigned long eviction;
284 : 0 : struct lruvec *lruvec;
285 : 0 : unsigned long refault;
286 : 0 : bool workingset;
287 : 0 : int memcgid;
288 : :
289 : 0 : unpack_shadow(shadow, &memcgid, &pgdat, &eviction, &workingset);
290 : :
291 : 0 : rcu_read_lock();
292 : : /*
293 : : * Look up the memcg associated with the stored ID. It might
294 : : * have been deleted since the page's eviction.
295 : : *
296 : : * Note that in rare events the ID could have been recycled
297 : : * for a new cgroup that refaults a shared page. This is
298 : : * impossible to tell from the available data. However, this
299 : : * should be a rare and limited disturbance, and activations
300 : : * are always speculative anyway. Ultimately, it's the aging
301 : : * algorithm's job to shake out the minimum access frequency
302 : : * for the active cache.
303 : : *
304 : : * XXX: On !CONFIG_MEMCG, this will always return NULL; it
305 : : * would be better if the root_mem_cgroup existed in all
306 : : * configurations instead.
307 : : */
308 : 0 : eviction_memcg = mem_cgroup_from_id(memcgid);
309 : 0 : if (!mem_cgroup_disabled() && !eviction_memcg)
310 : : goto out;
311 : 0 : eviction_lruvec = mem_cgroup_lruvec(eviction_memcg, pgdat);
312 : 0 : refault = atomic_long_read(&eviction_lruvec->inactive_age);
313 : 0 : active_file = lruvec_page_state(eviction_lruvec, NR_ACTIVE_FILE);
314 : :
315 : : /*
316 : : * Calculate the refault distance
317 : : *
318 : : * The unsigned subtraction here gives an accurate distance
319 : : * across inactive_age overflows in most cases. There is a
320 : : * special case: usually, shadow entries have a short lifetime
321 : : * and are either refaulted or reclaimed along with the inode
322 : : * before they get too old. But it is not impossible for the
323 : : * inactive_age to lap a shadow entry in the field, which can
324 : : * then result in a false small refault distance, leading to a
325 : : * false activation should this old entry actually refault
326 : : * again. However, earlier kernels used to deactivate
327 : : * unconditionally with *every* reclaim invocation for the
328 : : * longest time, so the occasional inappropriate activation
329 : : * leading to pressure on the active list is not a problem.
330 : : */
331 : 0 : refault_distance = (refault - eviction) & EVICTION_MASK;
332 : :
333 : : /*
334 : : * The activation decision for this page is made at the level
335 : : * where the eviction occurred, as that is where the LRU order
336 : : * during page reclaim is being determined.
337 : : *
338 : : * However, the cgroup that will own the page is the one that
339 : : * is actually experiencing the refault event.
340 : : */
341 : 0 : memcg = page_memcg(page);
342 : 0 : lruvec = mem_cgroup_lruvec(memcg, pgdat);
343 : :
344 : 0 : inc_lruvec_state(lruvec, WORKINGSET_REFAULT);
345 : :
346 : : /*
347 : : * Compare the distance to the existing workingset size. We
348 : : * don't act on pages that couldn't stay resident even if all
349 : : * the memory was available to the page cache.
350 : : */
351 [ # # ]: 0 : if (refault_distance > active_file)
352 : 0 : goto out;
353 : :
354 [ # # ]: 0 : SetPageActive(page);
355 : 0 : advance_inactive_age(memcg, pgdat);
356 : 0 : inc_lruvec_state(lruvec, WORKINGSET_ACTIVATE);
357 : :
358 : : /* Page was active prior to eviction */
359 [ # # ]: 0 : if (workingset) {
360 [ # # ]: 0 : SetPageWorkingset(page);
361 : 0 : inc_lruvec_state(lruvec, WORKINGSET_RESTORE);
362 : : }
363 : 0 : out:
364 : 0 : rcu_read_unlock();
365 : 0 : }
366 : :
367 : : /**
368 : : * workingset_activation - note a page activation
369 : : * @page: page that is being activated
370 : : */
371 : 96430 : void workingset_activation(struct page *page)
372 : : {
373 : 96430 : struct mem_cgroup *memcg;
374 : :
375 : 96430 : rcu_read_lock();
376 : : /*
377 : : * Filter non-memcg pages here, e.g. unmap can call
378 : : * mark_page_accessed() on VDSO pages.
379 : : *
380 : : * XXX: See workingset_refault() - this should return
381 : : * root_mem_cgroup even for !CONFIG_MEMCG.
382 : : */
383 : 96430 : memcg = page_memcg_rcu(page);
384 : 96430 : if (!mem_cgroup_disabled() && !memcg)
385 : : goto out;
386 : 96430 : advance_inactive_age(memcg, page_pgdat(page));
387 : : out:
388 : 96430 : rcu_read_unlock();
389 : 96430 : }
390 : :
391 : : /*
392 : : * Shadow entries reflect the share of the working set that does not
393 : : * fit into memory, so their number depends on the access pattern of
394 : : * the workload. In most cases, they will refault or get reclaimed
395 : : * along with the inode, but a (malicious) workload that streams
396 : : * through files with a total size several times that of available
397 : : * memory, while preventing the inodes from being reclaimed, can
398 : : * create excessive amounts of shadow nodes. To keep a lid on this,
399 : : * track shadow nodes and reclaim them when they grow way past the
400 : : * point where they would still be useful.
401 : : */
402 : :
403 : : static struct list_lru shadow_nodes;
404 : :
405 : 283766 : void workingset_update_node(struct xa_node *node)
406 : : {
407 : : /*
408 : : * Track non-empty nodes that contain only shadow entries;
409 : : * unlink those that contain pages or are being freed.
410 : : *
411 : : * Avoid acquiring the list_lru lock when the nodes are
412 : : * already where they should be. The list_empty() test is safe
413 : : * as node->private_list is protected by the i_pages lock.
414 : : */
415 : 283766 : VM_WARN_ON_ONCE(!irqs_disabled()); /* For __inc_lruvec_page_state */
416 : :
417 [ + + - + ]: 283766 : if (node->count && node->count == node->nr_values) {
418 [ # # ]: 0 : if (list_empty(&node->private_list)) {
419 : 0 : list_lru_add(&shadow_nodes, &node->private_list);
420 : 0 : __inc_lruvec_slab_state(node, WORKINGSET_NODES);
421 : : }
422 : : } else {
423 [ - + ]: 283766 : if (!list_empty(&node->private_list)) {
424 : 0 : list_lru_del(&shadow_nodes, &node->private_list);
425 : 0 : __dec_lruvec_slab_state(node, WORKINGSET_NODES);
426 : : }
427 : : }
428 : 283766 : }
429 : :
430 : 0 : static unsigned long count_shadow_nodes(struct shrinker *shrinker,
431 : : struct shrink_control *sc)
432 : : {
433 : 0 : unsigned long max_nodes;
434 : 0 : unsigned long nodes;
435 : 0 : unsigned long pages;
436 : :
437 : 0 : nodes = list_lru_shrink_count(&shadow_nodes, sc);
438 : :
439 : : /*
440 : : * Approximate a reasonable limit for the nodes
441 : : * containing shadow entries. We don't need to keep more
442 : : * shadow entries than possible pages on the active list,
443 : : * since refault distances bigger than that are dismissed.
444 : : *
445 : : * The size of the active list converges toward 100% of
446 : : * overall page cache as memory grows, with only a tiny
447 : : * inactive list. Assume the total cache size for that.
448 : : *
449 : : * Nodes might be sparsely populated, with only one shadow
450 : : * entry in the extreme case. Obviously, we cannot keep one
451 : : * node for every eligible shadow entry, so compromise on a
452 : : * worst-case density of 1/8th. Below that, not all eligible
453 : : * refaults can be detected anymore.
454 : : *
455 : : * On 64-bit with 7 xa_nodes per page and 64 slots
456 : : * each, this will reclaim shadow entries when they consume
457 : : * ~1.8% of available memory:
458 : : *
459 : : * PAGE_SIZE / xa_nodes / node_entries * 8 / PAGE_SIZE
460 : : */
461 : : #ifdef CONFIG_MEMCG
462 : : if (sc->memcg) {
463 : : struct lruvec *lruvec;
464 : : int i;
465 : :
466 : : lruvec = mem_cgroup_lruvec(sc->memcg, NODE_DATA(sc->nid));
467 : : for (pages = 0, i = 0; i < NR_LRU_LISTS; i++)
468 : : pages += lruvec_page_state_local(lruvec,
469 : : NR_LRU_BASE + i);
470 : : pages += lruvec_page_state_local(lruvec, NR_SLAB_RECLAIMABLE);
471 : : pages += lruvec_page_state_local(lruvec, NR_SLAB_UNRECLAIMABLE);
472 : : } else
473 : : #endif
474 : 0 : pages = node_present_pages(sc->nid);
475 : :
476 : 0 : max_nodes = pages >> (XA_CHUNK_SHIFT - 3);
477 : :
478 [ # # ]: 0 : if (!nodes)
479 : : return SHRINK_EMPTY;
480 : :
481 [ # # ]: 0 : if (nodes <= max_nodes)
482 : : return 0;
483 : 0 : return nodes - max_nodes;
484 : : }
485 : :
486 : 0 : static enum lru_status shadow_lru_isolate(struct list_head *item,
487 : : struct list_lru_one *lru,
488 : : spinlock_t *lru_lock,
489 : : void *arg) __must_hold(lru_lock)
490 : : {
491 : 0 : struct xa_node *node = container_of(item, struct xa_node, private_list);
492 : 0 : XA_STATE(xas, node->array, 0);
493 : 0 : struct address_space *mapping;
494 : 0 : int ret;
495 : :
496 : : /*
497 : : * Page cache insertions and deletions synchroneously maintain
498 : : * the shadow node LRU under the i_pages lock and the
499 : : * lru_lock. Because the page cache tree is emptied before
500 : : * the inode can be destroyed, holding the lru_lock pins any
501 : : * address_space that has nodes on the LRU.
502 : : *
503 : : * We can then safely transition to the i_pages lock to
504 : : * pin only the address_space of the particular node we want
505 : : * to reclaim, take the node off-LRU, and drop the lru_lock.
506 : : */
507 : :
508 : 0 : mapping = container_of(node->array, struct address_space, i_pages);
509 : :
510 : : /* Coming from the list, invert the lock order */
511 [ # # ]: 0 : if (!xa_trylock(&mapping->i_pages)) {
512 : 0 : spin_unlock_irq(lru_lock);
513 : 0 : ret = LRU_RETRY;
514 : 0 : goto out;
515 : : }
516 : :
517 : 0 : list_lru_isolate(lru, item);
518 : 0 : __dec_lruvec_slab_state(node, WORKINGSET_NODES);
519 : :
520 : 0 : spin_unlock(lru_lock);
521 : :
522 : : /*
523 : : * The nodes should only contain one or more shadow entries,
524 : : * no pages, so we expect to be able to remove them all and
525 : : * delete and free the empty node afterwards.
526 : : */
527 [ # # # # ]: 0 : if (WARN_ON_ONCE(!node->nr_values))
528 : 0 : goto out_invalid;
529 [ # # # # ]: 0 : if (WARN_ON_ONCE(node->count != node->nr_values))
530 : 0 : goto out_invalid;
531 : 0 : mapping->nrexceptional -= node->nr_values;
532 : 0 : xas.xa_node = xa_parent_locked(&mapping->i_pages, node);
533 : 0 : xas.xa_offset = node->offset;
534 : 0 : xas.xa_shift = node->shift + XA_CHUNK_SHIFT;
535 : 0 : xas_set_update(&xas, workingset_update_node);
536 : : /*
537 : : * We could store a shadow entry here which was the minimum of the
538 : : * shadow entries we were tracking ...
539 : : */
540 : 0 : xas_store(&xas, NULL);
541 : 0 : __inc_lruvec_slab_state(node, WORKINGSET_NODERECLAIM);
542 : :
543 : 0 : out_invalid:
544 : 0 : xa_unlock_irq(&mapping->i_pages);
545 : 0 : ret = LRU_REMOVED_RETRY;
546 : 0 : out:
547 : 0 : cond_resched();
548 : 0 : spin_lock_irq(lru_lock);
549 : 0 : return ret;
550 : : }
551 : :
552 : 0 : static unsigned long scan_shadow_nodes(struct shrinker *shrinker,
553 : : struct shrink_control *sc)
554 : : {
555 : : /* list_lru lock nests inside the IRQ-safe i_pages lock */
556 : 0 : return list_lru_shrink_walk_irq(&shadow_nodes, sc, shadow_lru_isolate,
557 : : NULL);
558 : : }
559 : :
560 : : static struct shrinker workingset_shadow_shrinker = {
561 : : .count_objects = count_shadow_nodes,
562 : : .scan_objects = scan_shadow_nodes,
563 : : .seeks = 0, /* ->count reports only fully expendable nodes */
564 : : .flags = SHRINKER_NUMA_AWARE | SHRINKER_MEMCG_AWARE,
565 : : };
566 : :
567 : : /*
568 : : * Our list_lru->lock is IRQ-safe as it nests inside the IRQ-safe
569 : : * i_pages lock.
570 : : */
571 : : static struct lock_class_key shadow_nodes_key;
572 : :
573 : 21 : static int __init workingset_init(void)
574 : : {
575 : 21 : unsigned int timestamp_bits;
576 : 21 : unsigned int max_order;
577 : 21 : int ret;
578 : :
579 : 21 : BUILD_BUG_ON(BITS_PER_LONG < EVICTION_SHIFT);
580 : : /*
581 : : * Calculate the eviction bucket size to cover the longest
582 : : * actionable refault distance, which is currently half of
583 : : * memory (totalram_pages/2). However, memory hotplug may add
584 : : * some more pages at runtime, so keep working with up to
585 : : * double the initial memory by using totalram_pages as-is.
586 : : */
587 : 21 : timestamp_bits = BITS_PER_LONG - EVICTION_SHIFT;
588 [ - + ]: 21 : max_order = fls_long(totalram_pages() - 1);
589 [ - + ]: 21 : if (max_order > timestamp_bits)
590 : 0 : bucket_order = max_order - timestamp_bits;
591 : 21 : pr_info("workingset: timestamp_bits=%d max_order=%d bucket_order=%u\n",
592 : : timestamp_bits, max_order, bucket_order);
593 : :
594 : 21 : ret = prealloc_shrinker(&workingset_shadow_shrinker);
595 [ - + ]: 21 : if (ret)
596 : 0 : goto err;
597 : 21 : ret = __list_lru_init(&shadow_nodes, true, &shadow_nodes_key,
598 : : &workingset_shadow_shrinker);
599 [ - + ]: 21 : if (ret)
600 : 0 : goto err_list_lru;
601 : 21 : register_shrinker_prepared(&workingset_shadow_shrinker);
602 : 21 : return 0;
603 : : err_list_lru:
604 : 0 : free_prealloced_shrinker(&workingset_shadow_shrinker);
605 : : err:
606 : : return ret;
607 : : }
608 : : module_init(workingset_init);
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