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);