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>
24 * Per node, two clock lists are maintained for file pages: the
25 * inactive and the active list. Freshly faulted pages start out at
26 * the head of the inactive list and page reclaim scans pages from the
27 * tail. Pages that are accessed multiple times on the inactive list
28 * are promoted to the active list, to protect them from reclaim,
29 * whereas active pages are demoted to the inactive list when the
30 * active list grows too big.
32 * fault ------------------------+
34 * +--------------+ | +-------------+
35 * reclaim <- | inactive | <-+-- demotion | active | <--+
36 * +--------------+ +-------------+ |
38 * +-------------- promotion ------------------+
41 * Access frequency and refault distance
43 * A workload is thrashing when its pages are frequently used but they
44 * are evicted from the inactive list every time before another access
45 * would have promoted them to the active list.
47 * In cases where the average access distance between thrashing pages
48 * is bigger than the size of memory there is nothing that can be
49 * done - the thrashing set could never fit into memory under any
52 * However, the average access distance could be bigger than the
53 * inactive list, yet smaller than the size of memory. In this case,
54 * the set could fit into memory if it weren't for the currently
55 * active pages - which may be used more, hopefully less frequently:
57 * +-memory available to cache-+
59 * +-inactive------+-active----+
60 * a b | c d e f g h i | J K L M N |
61 * +---------------+-----------+
63 * It is prohibitively expensive to accurately track access frequency
64 * of pages. But a reasonable approximation can be made to measure
65 * thrashing on the inactive list, after which refaulting pages can be
66 * activated optimistically to compete with the existing active pages.
68 * Approximating inactive page access frequency - Observations:
70 * 1. When a page is accessed for the first time, it is added to the
71 * head of the inactive list, slides every existing inactive page
72 * towards the tail by one slot, and pushes the current tail page
75 * 2. When a page is accessed for the second time, it is promoted to
76 * the active list, shrinking the inactive list by one slot. This
77 * also slides all inactive pages that were faulted into the cache
78 * more recently than the activated page towards the tail of the
83 * 1. The sum of evictions and activations between any two points in
84 * time indicate the minimum number of inactive pages accessed in
87 * 2. Moving one inactive page N page slots towards the tail of the
88 * list requires at least N inactive page accesses.
92 * 1. When a page is finally evicted from memory, the number of
93 * inactive pages accessed while the page was in cache is at least
94 * the number of page slots on the inactive list.
96 * 2. In addition, measuring the sum of evictions and activations (E)
97 * at the time of a page's eviction, and comparing it to another
98 * reading (R) at the time the page faults back into memory tells
99 * the minimum number of accesses while the page was not cached.
100 * This is called the refault distance.
102 * Because the first access of the page was the fault and the second
103 * access the refault, we combine the in-cache distance with the
104 * out-of-cache distance to get the complete minimum access distance
107 * NR_inactive + (R - E)
109 * And knowing the minimum access distance of a page, we can easily
110 * tell if the page would be able to stay in cache assuming all page
111 * slots in the cache were available:
113 * NR_inactive + (R - E) <= NR_inactive + NR_active
115 * If we have swap we should consider about NR_inactive_anon and
116 * NR_active_anon, so for page cache and anonymous respectively:
118 * NR_inactive_file + (R - E) <= NR_inactive_file + NR_active_file
119 * + NR_inactive_anon + NR_active_anon
121 * NR_inactive_anon + (R - E) <= NR_inactive_anon + NR_active_anon
122 * + NR_inactive_file + NR_active_file
124 * Which can be further simplified to:
126 * (R - E) <= NR_active_file + NR_inactive_anon + NR_active_anon
128 * (R - E) <= NR_active_anon + NR_inactive_file + NR_active_file
130 * Put into words, the refault distance (out-of-cache) can be seen as
131 * a deficit in inactive list space (in-cache). If the inactive list
132 * had (R - E) more page slots, the page would not have been evicted
133 * in between accesses, but activated instead. And on a full system,
134 * the only thing eating into inactive list space is active pages.
137 * Refaulting inactive pages
139 * All that is known about the active list is that the pages have been
140 * accessed more than once in the past. This means that at any given
141 * time there is actually a good chance that pages on the active list
142 * are no longer in active use.
144 * So when a refault distance of (R - E) is observed and there are at
145 * least (R - E) pages in the userspace workingset, the refaulting page
146 * is activated optimistically in the hope that (R - E) pages are actually
147 * used less frequently than the refaulting page - or even not used at
150 * That means if inactive cache is refaulting with a suitable refault
151 * distance, we assume the cache workingset is transitioning and put
152 * pressure on the current workingset.
154 * If this is wrong and demotion kicks in, the pages which are truly
155 * used more frequently will be reactivated while the less frequently
156 * used once will be evicted from memory.
158 * But if this is right, the stale pages will be pushed out of memory
159 * and the used pages get to stay in cache.
161 * Refaulting active pages
163 * If on the other hand the refaulting pages have recently been
164 * deactivated, it means that the active list is no longer protecting
165 * actively used cache from reclaim. The cache is NOT transitioning to
166 * a different workingset; the existing workingset is thrashing in the
167 * space allocated to the page cache.
172 * For each node's LRU lists, a counter for inactive evictions and
173 * activations is maintained (node->nonresident_age).
175 * On eviction, a snapshot of this counter (along with some bits to
176 * identify the node) is stored in the now empty page cache
177 * slot of the evicted page. This is called a shadow entry.
179 * On cache misses for which there are shadow entries, an eligible
180 * refault distance will immediately activate the refaulting page.
183 #define WORKINGSET_SHIFT 1
184 #define EVICTION_SHIFT ((BITS_PER_LONG - BITS_PER_XA_VALUE) + \
185 WORKINGSET_SHIFT + NODES_SHIFT + \
187 #define EVICTION_MASK (~0UL >> EVICTION_SHIFT)
190 * Eviction timestamps need to be able to cover the full range of
191 * actionable refaults. However, bits are tight in the xarray
192 * entry, and after storing the identifier for the lruvec there might
193 * not be enough left to represent every single actionable refault. In
194 * that case, we have to sacrifice granularity for distance, and group
195 * evictions into coarser buckets by shaving off lower timestamp bits.
197 static unsigned int bucket_order __read_mostly
;
199 static void *pack_shadow(int memcgid
, pg_data_t
*pgdat
, unsigned long eviction
,
202 eviction
&= EVICTION_MASK
;
203 eviction
= (eviction
<< MEM_CGROUP_ID_SHIFT
) | memcgid
;
204 eviction
= (eviction
<< NODES_SHIFT
) | pgdat
->node_id
;
205 eviction
= (eviction
<< WORKINGSET_SHIFT
) | workingset
;
207 return xa_mk_value(eviction
);
210 static void unpack_shadow(void *shadow
, int *memcgidp
, pg_data_t
**pgdat
,
211 unsigned long *evictionp
, bool *workingsetp
)
213 unsigned long entry
= xa_to_value(shadow
);
217 workingset
= entry
& ((1UL << WORKINGSET_SHIFT
) - 1);
218 entry
>>= WORKINGSET_SHIFT
;
219 nid
= entry
& ((1UL << NODES_SHIFT
) - 1);
220 entry
>>= NODES_SHIFT
;
221 memcgid
= entry
& ((1UL << MEM_CGROUP_ID_SHIFT
) - 1);
222 entry
>>= MEM_CGROUP_ID_SHIFT
;
225 *pgdat
= NODE_DATA(nid
);
227 *workingsetp
= workingset
;
230 #ifdef CONFIG_LRU_GEN
232 static void *lru_gen_eviction(struct folio
*folio
)
236 unsigned long min_seq
;
237 struct lruvec
*lruvec
;
238 struct lru_gen_folio
*lrugen
;
239 int type
= folio_is_file_lru(folio
);
240 int delta
= folio_nr_pages(folio
);
241 int refs
= folio_lru_refs(folio
);
242 int tier
= lru_tier_from_refs(refs
);
243 struct mem_cgroup
*memcg
= folio_memcg(folio
);
244 struct pglist_data
*pgdat
= folio_pgdat(folio
);
246 BUILD_BUG_ON(LRU_GEN_WIDTH
+ LRU_REFS_WIDTH
> BITS_PER_LONG
- EVICTION_SHIFT
);
248 lruvec
= mem_cgroup_lruvec(memcg
, pgdat
);
249 lrugen
= &lruvec
->lrugen
;
250 min_seq
= READ_ONCE(lrugen
->min_seq
[type
]);
251 token
= (min_seq
<< LRU_REFS_WIDTH
) | max(refs
- 1, 0);
253 hist
= lru_hist_from_seq(min_seq
);
254 atomic_long_add(delta
, &lrugen
->evicted
[hist
][type
][tier
]);
256 return pack_shadow(mem_cgroup_id(memcg
), pgdat
, token
, refs
);
260 * Tests if the shadow entry is for a folio that was recently evicted.
261 * Fills in @lruvec, @token, @workingset with the values unpacked from shadow.
263 static bool lru_gen_test_recent(void *shadow
, bool file
, struct lruvec
**lruvec
,
264 unsigned long *token
, bool *workingset
)
267 unsigned long min_seq
;
268 struct mem_cgroup
*memcg
;
269 struct pglist_data
*pgdat
;
271 unpack_shadow(shadow
, &memcg_id
, &pgdat
, token
, workingset
);
273 memcg
= mem_cgroup_from_id(memcg_id
);
274 *lruvec
= mem_cgroup_lruvec(memcg
, pgdat
);
276 min_seq
= READ_ONCE((*lruvec
)->lrugen
.min_seq
[file
]);
277 return (*token
>> LRU_REFS_WIDTH
) == (min_seq
& (EVICTION_MASK
>> LRU_REFS_WIDTH
));
280 static void lru_gen_refault(struct folio
*folio
, void *shadow
)
283 int hist
, tier
, refs
;
286 struct lruvec
*lruvec
;
287 struct lru_gen_folio
*lrugen
;
288 int type
= folio_is_file_lru(folio
);
289 int delta
= folio_nr_pages(folio
);
293 recent
= lru_gen_test_recent(shadow
, type
, &lruvec
, &token
, &workingset
);
294 if (lruvec
!= folio_lruvec(folio
))
297 mod_lruvec_state(lruvec
, WORKINGSET_REFAULT_BASE
+ type
, delta
);
302 lrugen
= &lruvec
->lrugen
;
304 hist
= lru_hist_from_seq(READ_ONCE(lrugen
->min_seq
[type
]));
305 /* see the comment in folio_lru_refs() */
306 refs
= (token
& (BIT(LRU_REFS_WIDTH
) - 1)) + workingset
;
307 tier
= lru_tier_from_refs(refs
);
309 atomic_long_add(delta
, &lrugen
->refaulted
[hist
][type
][tier
]);
310 mod_lruvec_state(lruvec
, WORKINGSET_ACTIVATE_BASE
+ type
, delta
);
313 * Count the following two cases as stalls:
314 * 1. For pages accessed through page tables, hotter pages pushed out
315 * hot pages which refaulted immediately.
316 * 2. For pages accessed multiple times through file descriptors,
317 * they would have been protected by sort_folio().
319 if (lru_gen_in_fault() || refs
>= BIT(LRU_REFS_WIDTH
) - 1) {
320 set_mask_bits(&folio
->flags
, 0, LRU_REFS_MASK
| BIT(PG_workingset
));
321 mod_lruvec_state(lruvec
, WORKINGSET_RESTORE_BASE
+ type
, delta
);
327 #else /* !CONFIG_LRU_GEN */
329 static void *lru_gen_eviction(struct folio
*folio
)
334 static bool lru_gen_test_recent(void *shadow
, bool file
, struct lruvec
**lruvec
,
335 unsigned long *token
, bool *workingset
)
340 static void lru_gen_refault(struct folio
*folio
, void *shadow
)
344 #endif /* CONFIG_LRU_GEN */
347 * workingset_age_nonresident - age non-resident entries as LRU ages
348 * @lruvec: the lruvec that was aged
349 * @nr_pages: the number of pages to count
351 * As in-memory pages are aged, non-resident pages need to be aged as
352 * well, in order for the refault distances later on to be comparable
353 * to the in-memory dimensions. This function allows reclaim and LRU
354 * operations to drive the non-resident aging along in parallel.
356 void workingset_age_nonresident(struct lruvec
*lruvec
, unsigned long nr_pages
)
359 * Reclaiming a cgroup means reclaiming all its children in a
360 * round-robin fashion. That means that each cgroup has an LRU
361 * order that is composed of the LRU orders of its child
362 * cgroups; and every page has an LRU position not just in the
363 * cgroup that owns it, but in all of that group's ancestors.
365 * So when the physical inactive list of a leaf cgroup ages,
366 * the virtual inactive lists of all its parents, including
367 * the root cgroup's, age as well.
370 atomic_long_add(nr_pages
, &lruvec
->nonresident_age
);
371 } while ((lruvec
= parent_lruvec(lruvec
)));
375 * workingset_eviction - note the eviction of a folio from memory
376 * @target_memcg: the cgroup that is causing the reclaim
377 * @folio: the folio being evicted
379 * Return: a shadow entry to be stored in @folio->mapping->i_pages in place
380 * of the evicted @folio so that a later refault can be detected.
382 void *workingset_eviction(struct folio
*folio
, struct mem_cgroup
*target_memcg
)
384 struct pglist_data
*pgdat
= folio_pgdat(folio
);
385 unsigned long eviction
;
386 struct lruvec
*lruvec
;
389 /* Folio is fully exclusive and pins folio's memory cgroup pointer */
390 VM_BUG_ON_FOLIO(folio_test_lru(folio
), folio
);
391 VM_BUG_ON_FOLIO(folio_ref_count(folio
), folio
);
392 VM_BUG_ON_FOLIO(!folio_test_locked(folio
), folio
);
394 if (lru_gen_enabled())
395 return lru_gen_eviction(folio
);
397 lruvec
= mem_cgroup_lruvec(target_memcg
, pgdat
);
398 /* XXX: target_memcg can be NULL, go through lruvec */
399 memcgid
= mem_cgroup_id(lruvec_memcg(lruvec
));
400 eviction
= atomic_long_read(&lruvec
->nonresident_age
);
401 eviction
>>= bucket_order
;
402 workingset_age_nonresident(lruvec
, folio_nr_pages(folio
));
403 return pack_shadow(memcgid
, pgdat
, eviction
,
404 folio_test_workingset(folio
));
408 * workingset_test_recent - tests if the shadow entry is for a folio that was
409 * recently evicted. Also fills in @workingset with the value unpacked from
411 * @shadow: the shadow entry to be tested.
412 * @file: whether the corresponding folio is from the file lru.
413 * @workingset: where the workingset value unpacked from shadow should
416 * Return: true if the shadow is for a recently evicted folio; false otherwise.
418 bool workingset_test_recent(void *shadow
, bool file
, bool *workingset
)
420 struct mem_cgroup
*eviction_memcg
;
421 struct lruvec
*eviction_lruvec
;
422 unsigned long refault_distance
;
423 unsigned long workingset_size
;
424 unsigned long refault
;
426 struct pglist_data
*pgdat
;
427 unsigned long eviction
;
431 if (lru_gen_enabled()) {
432 bool recent
= lru_gen_test_recent(shadow
, file
,
433 &eviction_lruvec
, &eviction
, workingset
);
440 unpack_shadow(shadow
, &memcgid
, &pgdat
, &eviction
, workingset
);
441 eviction
<<= bucket_order
;
444 * Look up the memcg associated with the stored ID. It might
445 * have been deleted since the folio's eviction.
447 * Note that in rare events the ID could have been recycled
448 * for a new cgroup that refaults a shared folio. This is
449 * impossible to tell from the available data. However, this
450 * should be a rare and limited disturbance, and activations
451 * are always speculative anyway. Ultimately, it's the aging
452 * algorithm's job to shake out the minimum access frequency
453 * for the active cache.
455 * XXX: On !CONFIG_MEMCG, this will always return NULL; it
456 * would be better if the root_mem_cgroup existed in all
457 * configurations instead.
459 eviction_memcg
= mem_cgroup_from_id(memcgid
);
460 if (!mem_cgroup_disabled() &&
461 (!eviction_memcg
|| !mem_cgroup_tryget(eviction_memcg
))) {
469 * Flush stats (and potentially sleep) outside the RCU read section.
470 * XXX: With per-memcg flushing and thresholding, is ratelimiting
473 mem_cgroup_flush_stats_ratelimited(eviction_memcg
);
475 eviction_lruvec
= mem_cgroup_lruvec(eviction_memcg
, pgdat
);
476 refault
= atomic_long_read(&eviction_lruvec
->nonresident_age
);
479 * Calculate the refault distance
481 * The unsigned subtraction here gives an accurate distance
482 * across nonresident_age overflows in most cases. There is a
483 * special case: usually, shadow entries have a short lifetime
484 * and are either refaulted or reclaimed along with the inode
485 * before they get too old. But it is not impossible for the
486 * nonresident_age to lap a shadow entry in the field, which
487 * can then result in a false small refault distance, leading
488 * to a false activation should this old entry actually
489 * refault again. However, earlier kernels used to deactivate
490 * unconditionally with *every* reclaim invocation for the
491 * longest time, so the occasional inappropriate activation
492 * leading to pressure on the active list is not a problem.
494 refault_distance
= (refault
- eviction
) & EVICTION_MASK
;
497 * Compare the distance to the existing workingset size. We
498 * don't activate pages that couldn't stay resident even if
499 * all the memory was available to the workingset. Whether
500 * workingset competition needs to consider anon or not depends
501 * on having free swap space.
503 workingset_size
= lruvec_page_state(eviction_lruvec
, NR_ACTIVE_FILE
);
505 workingset_size
+= lruvec_page_state(eviction_lruvec
,
508 if (mem_cgroup_get_nr_swap_pages(eviction_memcg
) > 0) {
509 workingset_size
+= lruvec_page_state(eviction_lruvec
,
512 workingset_size
+= lruvec_page_state(eviction_lruvec
,
517 mem_cgroup_put(eviction_memcg
);
518 return refault_distance
<= workingset_size
;
522 * workingset_refault - Evaluate the refault of a previously evicted folio.
523 * @folio: The freshly allocated replacement folio.
524 * @shadow: Shadow entry of the evicted folio.
526 * Calculates and evaluates the refault distance of the previously
527 * evicted folio in the context of the node and the memcg whose memory
528 * pressure caused the eviction.
530 void workingset_refault(struct folio
*folio
, void *shadow
)
532 bool file
= folio_is_file_lru(folio
);
533 struct pglist_data
*pgdat
;
534 struct mem_cgroup
*memcg
;
535 struct lruvec
*lruvec
;
539 if (lru_gen_enabled()) {
540 lru_gen_refault(folio
, shadow
);
545 * The activation decision for this folio is made at the level
546 * where the eviction occurred, as that is where the LRU order
547 * during folio reclaim is being determined.
549 * However, the cgroup that will own the folio is the one that
550 * is actually experiencing the refault event. Make sure the folio is
551 * locked to guarantee folio_memcg() stability throughout.
553 VM_BUG_ON_FOLIO(!folio_test_locked(folio
), folio
);
554 nr
= folio_nr_pages(folio
);
555 memcg
= folio_memcg(folio
);
556 pgdat
= folio_pgdat(folio
);
557 lruvec
= mem_cgroup_lruvec(memcg
, pgdat
);
559 mod_lruvec_state(lruvec
, WORKINGSET_REFAULT_BASE
+ file
, nr
);
561 if (!workingset_test_recent(shadow
, file
, &workingset
))
564 folio_set_active(folio
);
565 workingset_age_nonresident(lruvec
, nr
);
566 mod_lruvec_state(lruvec
, WORKINGSET_ACTIVATE_BASE
+ file
, nr
);
568 /* Folio was active prior to eviction */
570 folio_set_workingset(folio
);
572 * XXX: Move to folio_add_lru() when it supports new vs
575 lru_note_cost_refault(folio
);
576 mod_lruvec_state(lruvec
, WORKINGSET_RESTORE_BASE
+ file
, nr
);
581 * workingset_activation - note a page activation
582 * @folio: Folio that is being activated.
584 void workingset_activation(struct folio
*folio
)
586 struct mem_cgroup
*memcg
;
590 * Filter non-memcg pages here, e.g. unmap can call
591 * mark_page_accessed() on VDSO pages.
593 * XXX: See workingset_refault() - this should return
594 * root_mem_cgroup even for !CONFIG_MEMCG.
596 memcg
= folio_memcg_rcu(folio
);
597 if (!mem_cgroup_disabled() && !memcg
)
599 workingset_age_nonresident(folio_lruvec(folio
), folio_nr_pages(folio
));
605 * Shadow entries reflect the share of the working set that does not
606 * fit into memory, so their number depends on the access pattern of
607 * the workload. In most cases, they will refault or get reclaimed
608 * along with the inode, but a (malicious) workload that streams
609 * through files with a total size several times that of available
610 * memory, while preventing the inodes from being reclaimed, can
611 * create excessive amounts of shadow nodes. To keep a lid on this,
612 * track shadow nodes and reclaim them when they grow way past the
613 * point where they would still be useful.
616 struct list_lru shadow_nodes
;
618 void workingset_update_node(struct xa_node
*node
)
620 struct address_space
*mapping
;
623 * Track non-empty nodes that contain only shadow entries;
624 * unlink those that contain pages or are being freed.
626 * Avoid acquiring the list_lru lock when the nodes are
627 * already where they should be. The list_empty() test is safe
628 * as node->private_list is protected by the i_pages lock.
630 mapping
= container_of(node
->array
, struct address_space
, i_pages
);
631 lockdep_assert_held(&mapping
->i_pages
.xa_lock
);
633 if (node
->count
&& node
->count
== node
->nr_values
) {
634 if (list_empty(&node
->private_list
)) {
635 list_lru_add_obj(&shadow_nodes
, &node
->private_list
);
636 __inc_lruvec_kmem_state(node
, WORKINGSET_NODES
);
639 if (!list_empty(&node
->private_list
)) {
640 list_lru_del_obj(&shadow_nodes
, &node
->private_list
);
641 __dec_lruvec_kmem_state(node
, WORKINGSET_NODES
);
646 static unsigned long count_shadow_nodes(struct shrinker
*shrinker
,
647 struct shrink_control
*sc
)
649 unsigned long max_nodes
;
653 nodes
= list_lru_shrink_count(&shadow_nodes
, sc
);
658 * Approximate a reasonable limit for the nodes
659 * containing shadow entries. We don't need to keep more
660 * shadow entries than possible pages on the active list,
661 * since refault distances bigger than that are dismissed.
663 * The size of the active list converges toward 100% of
664 * overall page cache as memory grows, with only a tiny
665 * inactive list. Assume the total cache size for that.
667 * Nodes might be sparsely populated, with only one shadow
668 * entry in the extreme case. Obviously, we cannot keep one
669 * node for every eligible shadow entry, so compromise on a
670 * worst-case density of 1/8th. Below that, not all eligible
671 * refaults can be detected anymore.
673 * On 64-bit with 7 xa_nodes per page and 64 slots
674 * each, this will reclaim shadow entries when they consume
675 * ~1.8% of available memory:
677 * PAGE_SIZE / xa_nodes / node_entries * 8 / PAGE_SIZE
681 struct lruvec
*lruvec
;
684 mem_cgroup_flush_stats_ratelimited(sc
->memcg
);
685 lruvec
= mem_cgroup_lruvec(sc
->memcg
, NODE_DATA(sc
->nid
));
686 for (pages
= 0, i
= 0; i
< NR_LRU_LISTS
; i
++)
687 pages
+= lruvec_page_state_local(lruvec
,
689 pages
+= lruvec_page_state_local(
690 lruvec
, NR_SLAB_RECLAIMABLE_B
) >> PAGE_SHIFT
;
691 pages
+= lruvec_page_state_local(
692 lruvec
, NR_SLAB_UNRECLAIMABLE_B
) >> PAGE_SHIFT
;
695 pages
= node_present_pages(sc
->nid
);
697 max_nodes
= pages
>> (XA_CHUNK_SHIFT
- 3);
699 if (nodes
<= max_nodes
)
701 return nodes
- max_nodes
;
704 static enum lru_status
shadow_lru_isolate(struct list_head
*item
,
705 struct list_lru_one
*lru
,
706 spinlock_t
*lru_lock
,
707 void *arg
) __must_hold(lru_lock
)
709 struct xa_node
*node
= container_of(item
, struct xa_node
, private_list
);
710 struct address_space
*mapping
;
714 * Page cache insertions and deletions synchronously maintain
715 * the shadow node LRU under the i_pages lock and the
716 * lru_lock. Because the page cache tree is emptied before
717 * the inode can be destroyed, holding the lru_lock pins any
718 * address_space that has nodes on the LRU.
720 * We can then safely transition to the i_pages lock to
721 * pin only the address_space of the particular node we want
722 * to reclaim, take the node off-LRU, and drop the lru_lock.
725 mapping
= container_of(node
->array
, struct address_space
, i_pages
);
727 /* Coming from the list, invert the lock order */
728 if (!xa_trylock(&mapping
->i_pages
)) {
729 spin_unlock_irq(lru_lock
);
734 /* For page cache we need to hold i_lock */
735 if (mapping
->host
!= NULL
) {
736 if (!spin_trylock(&mapping
->host
->i_lock
)) {
737 xa_unlock(&mapping
->i_pages
);
738 spin_unlock_irq(lru_lock
);
744 list_lru_isolate(lru
, item
);
745 __dec_lruvec_kmem_state(node
, WORKINGSET_NODES
);
747 spin_unlock(lru_lock
);
750 * The nodes should only contain one or more shadow entries,
751 * no pages, so we expect to be able to remove them all and
752 * delete and free the empty node afterwards.
754 if (WARN_ON_ONCE(!node
->nr_values
))
756 if (WARN_ON_ONCE(node
->count
!= node
->nr_values
))
758 xa_delete_node(node
, workingset_update_node
);
759 __inc_lruvec_kmem_state(node
, WORKINGSET_NODERECLAIM
);
762 xa_unlock_irq(&mapping
->i_pages
);
763 if (mapping
->host
!= NULL
) {
764 if (mapping_shrinkable(mapping
))
765 inode_add_lru(mapping
->host
);
766 spin_unlock(&mapping
->host
->i_lock
);
768 ret
= LRU_REMOVED_RETRY
;
771 spin_lock_irq(lru_lock
);
775 static unsigned long scan_shadow_nodes(struct shrinker
*shrinker
,
776 struct shrink_control
*sc
)
778 /* list_lru lock nests inside the IRQ-safe i_pages lock */
779 return list_lru_shrink_walk_irq(&shadow_nodes
, sc
, shadow_lru_isolate
,
784 * Our list_lru->lock is IRQ-safe as it nests inside the IRQ-safe
787 static struct lock_class_key shadow_nodes_key
;
789 static int __init
workingset_init(void)
791 struct shrinker
*workingset_shadow_shrinker
;
792 unsigned int timestamp_bits
;
793 unsigned int max_order
;
796 BUILD_BUG_ON(BITS_PER_LONG
< EVICTION_SHIFT
);
798 * Calculate the eviction bucket size to cover the longest
799 * actionable refault distance, which is currently half of
800 * memory (totalram_pages/2). However, memory hotplug may add
801 * some more pages at runtime, so keep working with up to
802 * double the initial memory by using totalram_pages as-is.
804 timestamp_bits
= BITS_PER_LONG
- EVICTION_SHIFT
;
805 max_order
= fls_long(totalram_pages() - 1);
806 if (max_order
> timestamp_bits
)
807 bucket_order
= max_order
- timestamp_bits
;
808 pr_info("workingset: timestamp_bits=%d max_order=%d bucket_order=%u\n",
809 timestamp_bits
, max_order
, bucket_order
);
811 workingset_shadow_shrinker
= shrinker_alloc(SHRINKER_NUMA_AWARE
|
812 SHRINKER_MEMCG_AWARE
,
814 if (!workingset_shadow_shrinker
)
817 ret
= __list_lru_init(&shadow_nodes
, true, &shadow_nodes_key
,
818 workingset_shadow_shrinker
);
822 workingset_shadow_shrinker
->count_objects
= count_shadow_nodes
;
823 workingset_shadow_shrinker
->scan_objects
= scan_shadow_nodes
;
824 /* ->count reports only fully expendable nodes */
825 workingset_shadow_shrinker
->seeks
= 0;
827 shrinker_register(workingset_shadow_shrinker
);
830 shrinker_free(workingset_shadow_shrinker
);
834 module_init(workingset_init
);