1// SPDX-License-Identifier: GPL-2.0
2#include <linux/init.h>
3#include <linux/memblock.h>
4#include <linux/fs.h>
5#include <linux/sysfs.h>
6#include <linux/kobject.h>
7#include <linux/memory_hotplug.h>
8#include <linux/mm.h>
9#include <linux/mmzone.h>
10#include <linux/pagemap.h>
11#include <linux/rmap.h>
12#include <linux/mmu_notifier.h>
13#include <linux/page_ext.h>
14#include <linux/page_idle.h>
15
16#include "internal.h"
17
18#define BITMAP_CHUNK_SIZE	sizeof(u64)
19#define BITMAP_CHUNK_BITS	(BITMAP_CHUNK_SIZE * BITS_PER_BYTE)
20
21/*
22 * Idle page tracking only considers user memory pages, for other types of
23 * pages the idle flag is always unset and an attempt to set it is silently
24 * ignored.
25 *
26 * We treat a page as a user memory page if it is on an LRU list, because it is
27 * always safe to pass such a page to rmap_walk(), which is essential for idle
28 * page tracking. With such an indicator of user pages we can skip isolated
29 * pages, but since there are not usually many of them, it will hardly affect
30 * the overall result.
31 *
32 * This function tries to get a user memory page by pfn as described above.
33 */
34static struct folio *page_idle_get_folio(unsigned long pfn)
35{
36	struct page *page = pfn_to_online_page(pfn);
37	struct folio *folio;
38
39	if (!page || PageTail(page))
40		return NULL;
41
42	folio = page_folio(page);
43	if (!folio_test_lru(folio) || !folio_try_get(folio))
44		return NULL;
45	if (unlikely(page_folio(page) != folio || !folio_test_lru(folio))) {
46		folio_put(folio);
47		folio = NULL;
48	}
49	return folio;
50}
51
52static bool page_idle_clear_pte_refs_one(struct folio *folio,
53					struct vm_area_struct *vma,
54					unsigned long addr, void *arg)
55{
56	DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, addr, 0);
57	bool referenced = false;
58
59	while (page_vma_mapped_walk(&pvmw)) {
60		addr = pvmw.address;
61		if (pvmw.pte) {
62			/*
63			 * For PTE-mapped THP, one sub page is referenced,
64			 * the whole THP is referenced.
65			 */
66			if (ptep_clear_young_notify(vma, addr, pvmw.pte))
67				referenced = true;
68		} else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
69			if (pmdp_clear_young_notify(vma, addr, pvmw.pmd))
70				referenced = true;
71		} else {
72			/* unexpected pmd-mapped page? */
73			WARN_ON_ONCE(1);
74		}
75	}
76
77	if (referenced) {
78		folio_clear_idle(folio);
79		/*
80		 * We cleared the referenced bit in a mapping to this page. To
81		 * avoid interference with page reclaim, mark it young so that
82		 * folio_referenced() will return > 0.
83		 */
84		folio_set_young(folio);
85	}
86	return true;
87}
88
89static void page_idle_clear_pte_refs(struct folio *folio)
90{
91	/*
92	 * Since rwc.try_lock is unused, rwc is effectively immutable, so we
93	 * can make it static to save some cycles and stack.
94	 */
95	static struct rmap_walk_control rwc = {
96		.rmap_one = page_idle_clear_pte_refs_one,
97		.anon_lock = folio_lock_anon_vma_read,
98	};
99	bool need_lock;
100
101	if (!folio_mapped(folio) || !folio_raw_mapping(folio))
102		return;
103
104	need_lock = !folio_test_anon(folio) || folio_test_ksm(folio);
105	if (need_lock && !folio_trylock(folio))
106		return;
107
108	rmap_walk(folio, &rwc);
109
110	if (need_lock)
111		folio_unlock(folio);
112}
113
114static ssize_t page_idle_bitmap_read(struct file *file, struct kobject *kobj,
115				     struct bin_attribute *attr, char *buf,
116				     loff_t pos, size_t count)
117{
118	u64 *out = (u64 *)buf;
119	struct folio *folio;
120	unsigned long pfn, end_pfn;
121	int bit;
122
123	if (pos % BITMAP_CHUNK_SIZE || count % BITMAP_CHUNK_SIZE)
124		return -EINVAL;
125
126	pfn = pos * BITS_PER_BYTE;
127	if (pfn >= max_pfn)
128		return 0;
129
130	end_pfn = pfn + count * BITS_PER_BYTE;
131	if (end_pfn > max_pfn)
132		end_pfn = max_pfn;
133
134	for (; pfn < end_pfn; pfn++) {
135		bit = pfn % BITMAP_CHUNK_BITS;
136		if (!bit)
137			*out = 0ULL;
138		folio = page_idle_get_folio(pfn);
139		if (folio) {
140			if (folio_test_idle(folio)) {
141				/*
142				 * The page might have been referenced via a
143				 * pte, in which case it is not idle. Clear
144				 * refs and recheck.
145				 */
146				page_idle_clear_pte_refs(folio);
147				if (folio_test_idle(folio))
148					*out |= 1ULL << bit;
149			}
150			folio_put(folio);
151		}
152		if (bit == BITMAP_CHUNK_BITS - 1)
153			out++;
154		cond_resched();
155	}
156	return (char *)out - buf;
157}
158
159static ssize_t page_idle_bitmap_write(struct file *file, struct kobject *kobj,
160				      struct bin_attribute *attr, char *buf,
161				      loff_t pos, size_t count)
162{
163	const u64 *in = (u64 *)buf;
164	struct folio *folio;
165	unsigned long pfn, end_pfn;
166	int bit;
167
168	if (pos % BITMAP_CHUNK_SIZE || count % BITMAP_CHUNK_SIZE)
169		return -EINVAL;
170
171	pfn = pos * BITS_PER_BYTE;
172	if (pfn >= max_pfn)
173		return -ENXIO;
174
175	end_pfn = pfn + count * BITS_PER_BYTE;
176	if (end_pfn > max_pfn)
177		end_pfn = max_pfn;
178
179	for (; pfn < end_pfn; pfn++) {
180		bit = pfn % BITMAP_CHUNK_BITS;
181		if ((*in >> bit) & 1) {
182			folio = page_idle_get_folio(pfn);
183			if (folio) {
184				page_idle_clear_pte_refs(folio);
185				folio_set_idle(folio);
186				folio_put(folio);
187			}
188		}
189		if (bit == BITMAP_CHUNK_BITS - 1)
190			in++;
191		cond_resched();
192	}
193	return (char *)in - buf;
194}
195
196static struct bin_attribute page_idle_bitmap_attr =
197		__BIN_ATTR(bitmap, 0600,
198			   page_idle_bitmap_read, page_idle_bitmap_write, 0);
199
200static struct bin_attribute *page_idle_bin_attrs[] = {
201	&page_idle_bitmap_attr,
202	NULL,
203};
204
205static const struct attribute_group page_idle_attr_group = {
206	.bin_attrs = page_idle_bin_attrs,
207	.name = "page_idle",
208};
209
210static int __init page_idle_init(void)
211{
212	int err;
213
214	err = sysfs_create_group(mm_kobj, &page_idle_attr_group);
215	if (err) {
216		pr_err("page_idle: register sysfs failed\n");
217		return err;
218	}
219	return 0;
220}
221subsys_initcall(page_idle_init);
222