1 // SPDX-License-Identifier: GPL-2.0
5 * Copyright (C) 2013 Red Hat, Inc., Johannes Weiner
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>
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.
31 * fault ------------------------+
33 * +--------------+ | +-------------+
34 * reclaim <- | inactive | <-+-- demotion | active | <--+
35 * +--------------+ +-------------+ |
37 * +-------------- promotion ------------------+
40 * Access frequency and refault distance
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.
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
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:
56 * +-memory available to cache-+
58 * +-inactive------+-active----+
59 * a b | c d e f g h i | J K L M N |
60 * +---------------+-----------+
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.
67 * Approximating inactive page access frequency - Observations:
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
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
82 * 1. The sum of evictions and activations between any two points in
83 * time indicate the minimum number of inactive pages accessed in
86 * 2. Moving one inactive page N page slots towards the tail of the
87 * list requires at least N inactive page accesses.
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.
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.
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
106 * NR_inactive + (R - E)
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:
112 * NR_inactive + (R - E) <= NR_inactive + NR_active
114 * If we have swap we should consider about NR_inactive_anon and
115 * NR_active_anon, so for page cache and anonymous respectively:
117 * NR_inactive_file + (R - E) <= NR_inactive_file + NR_active_file
118 * + NR_inactive_anon + NR_active_anon
120 * NR_inactive_anon + (R - E) <= NR_inactive_anon + NR_active_anon
121 * + NR_inactive_file + NR_active_file
123 * Which can be further simplified to:
125 * (R - E) <= NR_active_file + NR_inactive_anon + NR_active_anon
127 * (R - E) <= NR_active_anon + NR_inactive_file + NR_active_file
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.
136 * Refaulting inactive pages
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.
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
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.
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.
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.
160 * Refaulting active pages
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.
171 * For each node's LRU lists, a counter for inactive evictions and
172 * activations is maintained (node->nonresident_age).
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.
178 * On cache misses for which there are shadow entries, an eligible
179 * refault distance will immediately activate the refaulting page.
182 #define WORKINGSET_SHIFT 1
183 #define EVICTION_SHIFT ((BITS_PER_LONG - BITS_PER_XA_VALUE) + \
184 WORKINGSET_SHIFT + NODES_SHIFT + \
186 #define EVICTION_MASK (~0UL >> EVICTION_SHIFT)
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.
196 static unsigned int bucket_order __read_mostly
;
198 static void *pack_shadow(int memcgid
, pg_data_t
*pgdat
, unsigned long eviction
,
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
;
206 return xa_mk_value(eviction
);
209 static void unpack_shadow(void *shadow
, int *memcgidp
, pg_data_t
**pgdat
,
210 unsigned long *evictionp
, bool *workingsetp
)
212 unsigned long entry
= xa_to_value(shadow
);
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
;
224 *pgdat
= NODE_DATA(nid
);
226 *workingsetp
= workingset
;
229 #ifdef CONFIG_LRU_GEN
231 static void *lru_gen_eviction(struct folio
*folio
)
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
);
245 BUILD_BUG_ON(LRU_GEN_WIDTH
+ LRU_REFS_WIDTH
> BITS_PER_LONG
- EVICTION_SHIFT
);
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);
252 hist
= lru_hist_from_seq(min_seq
);
253 atomic_long_add(delta
, &lrugen
->evicted
[hist
][type
][tier
]);
255 return pack_shadow(mem_cgroup_id(memcg
), pgdat
, token
, refs
);
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.
262 static bool lru_gen_test_recent(void *shadow
, bool file
, struct lruvec
**lruvec
,
263 unsigned long *token
, bool *workingset
)
266 unsigned long min_seq
;
267 struct mem_cgroup
*memcg
;
268 struct pglist_data
*pgdat
;
270 unpack_shadow(shadow
, &memcg_id
, &pgdat
, token
, workingset
);
272 memcg
= mem_cgroup_from_id(memcg_id
);
273 *lruvec
= mem_cgroup_lruvec(memcg
, pgdat
);
275 min_seq
= READ_ONCE((*lruvec
)->lrugen
.min_seq
[file
]);
276 return (*token
>> LRU_REFS_WIDTH
) == (min_seq
& (EVICTION_MASK
>> LRU_REFS_WIDTH
));
279 static void lru_gen_refault(struct folio
*folio
, void *shadow
)
282 int hist
, tier
, refs
;
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
);
292 recent
= lru_gen_test_recent(shadow
, type
, &lruvec
, &token
, &workingset
);
293 if (lruvec
!= folio_lruvec(folio
))
296 mod_lruvec_state(lruvec
, WORKINGSET_REFAULT_BASE
+ type
, delta
);
301 lrugen
= &lruvec
->lrugen
;
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
);
308 atomic_long_add(delta
, &lrugen
->refaulted
[hist
][type
][tier
]);
309 mod_lruvec_state(lruvec
, WORKINGSET_ACTIVATE_BASE
+ type
, delta
);
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.
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
);
326 #else /* !CONFIG_LRU_GEN */
328 static void *lru_gen_eviction(struct folio
*folio
)
333 static bool lru_gen_test_recent(void *shadow
, bool file
, struct lruvec
**lruvec
,
334 unsigned long *token
, bool *workingset
)
339 static void lru_gen_refault(struct folio
*folio
, void *shadow
)
343 #endif /* CONFIG_LRU_GEN */
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
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.
355 void workingset_age_nonresident(struct lruvec
*lruvec
, unsigned long nr_pages
)
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.
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.
369 atomic_long_add(nr_pages
, &lruvec
->nonresident_age
);
370 } while ((lruvec
= parent_lruvec(lruvec
)));
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
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.
381 void *workingset_eviction(struct folio
*folio
, struct mem_cgroup
*target_memcg
)
383 struct pglist_data
*pgdat
= folio_pgdat(folio
);
384 unsigned long eviction
;
385 struct lruvec
*lruvec
;
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
);
393 if (lru_gen_enabled())
394 return lru_gen_eviction(folio
);
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
));
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
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
415 * Return: true if the shadow is for a recently evicted folio; false otherwise.
417 bool workingset_test_recent(void *shadow
, bool file
, bool *workingset
)
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
;
425 struct pglist_data
*pgdat
;
426 unsigned long eviction
;
428 if (lru_gen_enabled())
429 return lru_gen_test_recent(shadow
, file
, &eviction_lruvec
, &eviction
, workingset
);
431 unpack_shadow(shadow
, &memcgid
, &pgdat
, &eviction
, workingset
);
432 eviction
<<= bucket_order
;
435 * Look up the memcg associated with the stored ID. It might
436 * have been deleted since the folio's eviction.
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.
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.
450 eviction_memcg
= mem_cgroup_from_id(memcgid
);
451 if (!mem_cgroup_disabled() && !eviction_memcg
)
454 eviction_lruvec
= mem_cgroup_lruvec(eviction_memcg
, pgdat
);
455 refault
= atomic_long_read(&eviction_lruvec
->nonresident_age
);
458 * Calculate the refault distance
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.
473 refault_distance
= (refault
- eviction
) & EVICTION_MASK
;
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.
482 workingset_size
= lruvec_page_state(eviction_lruvec
, NR_ACTIVE_FILE
);
484 workingset_size
+= lruvec_page_state(eviction_lruvec
,
487 if (mem_cgroup_get_nr_swap_pages(eviction_memcg
) > 0) {
488 workingset_size
+= lruvec_page_state(eviction_lruvec
,
491 workingset_size
+= lruvec_page_state(eviction_lruvec
,
496 return refault_distance
<= workingset_size
;
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.
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.
508 void workingset_refault(struct folio
*folio
, void *shadow
)
510 bool file
= folio_is_file_lru(folio
);
511 struct pglist_data
*pgdat
;
512 struct mem_cgroup
*memcg
;
513 struct lruvec
*lruvec
;
517 if (lru_gen_enabled()) {
518 lru_gen_refault(folio
, shadow
);
522 /* Flush stats (and potentially sleep) before holding RCU read lock */
523 mem_cgroup_flush_stats_ratelimited();
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.
532 * However, the cgroup that will own the folio is the one that
533 * is actually experiencing the refault event.
535 nr
= folio_nr_pages(folio
);
536 memcg
= folio_memcg(folio
);
537 pgdat
= folio_pgdat(folio
);
538 lruvec
= mem_cgroup_lruvec(memcg
, pgdat
);
540 mod_lruvec_state(lruvec
, WORKINGSET_REFAULT_BASE
+ file
, nr
);
542 if (!workingset_test_recent(shadow
, file
, &workingset
))
545 folio_set_active(folio
);
546 workingset_age_nonresident(lruvec
, nr
);
547 mod_lruvec_state(lruvec
, WORKINGSET_ACTIVATE_BASE
+ file
, nr
);
549 /* Folio was active prior to eviction */
551 folio_set_workingset(folio
);
553 * XXX: Move to folio_add_lru() when it supports new vs
556 lru_note_cost_refault(folio
);
557 mod_lruvec_state(lruvec
, WORKINGSET_RESTORE_BASE
+ file
, nr
);
564 * workingset_activation - note a page activation
565 * @folio: Folio that is being activated.
567 void workingset_activation(struct folio
*folio
)
569 struct mem_cgroup
*memcg
;
573 * Filter non-memcg pages here, e.g. unmap can call
574 * mark_page_accessed() on VDSO pages.
576 * XXX: See workingset_refault() - this should return
577 * root_mem_cgroup even for !CONFIG_MEMCG.
579 memcg
= folio_memcg_rcu(folio
);
580 if (!mem_cgroup_disabled() && !memcg
)
582 workingset_age_nonresident(folio_lruvec(folio
), folio_nr_pages(folio
));
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.
599 struct list_lru shadow_nodes
;
601 void workingset_update_node(struct xa_node
*node
)
603 struct address_space
*mapping
;
606 * Track non-empty nodes that contain only shadow entries;
607 * unlink those that contain pages or are being freed.
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.
613 mapping
= container_of(node
->array
, struct address_space
, i_pages
);
614 lockdep_assert_held(&mapping
->i_pages
.xa_lock
);
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
);
622 if (!list_empty(&node
->private_list
)) {
623 list_lru_del(&shadow_nodes
, &node
->private_list
);
624 __dec_lruvec_kmem_state(node
, WORKINGSET_NODES
);
629 static unsigned long count_shadow_nodes(struct shrinker
*shrinker
,
630 struct shrink_control
*sc
)
632 unsigned long max_nodes
;
636 nodes
= list_lru_shrink_count(&shadow_nodes
, sc
);
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.
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.
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.
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:
660 * PAGE_SIZE / xa_nodes / node_entries * 8 / PAGE_SIZE
664 struct lruvec
*lruvec
;
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
,
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
;
678 pages
= node_present_pages(sc
->nid
);
680 max_nodes
= pages
>> (XA_CHUNK_SHIFT
- 3);
682 if (nodes
<= max_nodes
)
684 return nodes
- max_nodes
;
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
)
692 struct xa_node
*node
= container_of(item
, struct xa_node
, private_list
);
693 struct address_space
*mapping
;
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.
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.
708 mapping
= container_of(node
->array
, struct address_space
, i_pages
);
710 /* Coming from the list, invert the lock order */
711 if (!xa_trylock(&mapping
->i_pages
)) {
712 spin_unlock_irq(lru_lock
);
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
);
727 list_lru_isolate(lru
, item
);
728 __dec_lruvec_kmem_state(node
, WORKINGSET_NODES
);
730 spin_unlock(lru_lock
);
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.
737 if (WARN_ON_ONCE(!node
->nr_values
))
739 if (WARN_ON_ONCE(node
->count
!= node
->nr_values
))
741 xa_delete_node(node
, workingset_update_node
);
742 __inc_lruvec_kmem_state(node
, WORKINGSET_NODERECLAIM
);
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
);
751 ret
= LRU_REMOVED_RETRY
;
754 spin_lock_irq(lru_lock
);
758 static unsigned long scan_shadow_nodes(struct shrinker
*shrinker
,
759 struct shrink_control
*sc
)
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
,
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
,
774 * Our list_lru->lock is IRQ-safe as it nests inside the IRQ-safe
777 static struct lock_class_key shadow_nodes_key
;
779 static int __init
workingset_init(void)
781 unsigned int timestamp_bits
;
782 unsigned int max_order
;
785 BUILD_BUG_ON(BITS_PER_LONG
< EVICTION_SHIFT
);
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.
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
);
800 ret
= prealloc_shrinker(&workingset_shadow_shrinker
, "mm-shadow");
803 ret
= __list_lru_init(&shadow_nodes
, true, &shadow_nodes_key
,
804 &workingset_shadow_shrinker
);
807 register_shrinker_prepared(&workingset_shadow_shrinker
);
810 free_prealloced_shrinker(&workingset_shadow_shrinker
);
814 module_init(workingset_init
);