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#define BITMAP_CHUNK_SIZE	sizeof(u64)
 17#define BITMAP_CHUNK_BITS	(BITMAP_CHUNK_SIZE * BITS_PER_BYTE)
 18
 19/*
 20 * Idle page tracking only considers user memory pages, for other types of
 21 * pages the idle flag is always unset and an attempt to set it is silently
 22 * ignored.
 23 *
 24 * We treat a page as a user memory page if it is on an LRU list, because it is
 25 * always safe to pass such a page to rmap_walk(), which is essential for idle
 26 * page tracking. With such an indicator of user pages we can skip isolated
 27 * pages, but since there are not usually many of them, it will hardly affect
 28 * the overall result.
 29 *
 30 * This function tries to get a user memory page by pfn as described above.
 31 */
 32static struct page *page_idle_get_page(unsigned long pfn)
 33{
 34	struct page *page = pfn_to_online_page(pfn);
 35	pg_data_t *pgdat;
 36
 37	if (!page || !PageLRU(page) ||
 38	    !get_page_unless_zero(page))
 39		return NULL;
 40
 41	pgdat = page_pgdat(page);
 42	spin_lock_irq(&pgdat->lru_lock);
 43	if (unlikely(!PageLRU(page))) {
 44		put_page(page);
 45		page = NULL;
 46	}
 47	spin_unlock_irq(&pgdat->lru_lock);
 48	return page;
 49}
 50
 51static bool page_idle_clear_pte_refs_one(struct page *page,
 52					struct vm_area_struct *vma,
 53					unsigned long addr, void *arg)
 54{
 55	struct page_vma_mapped_walk pvmw = {
 56		.page = page,
 57		.vma = vma,
 58		.address = addr,
 59	};
 60	bool referenced = false;
 61
 62	while (page_vma_mapped_walk(&pvmw)) {
 63		addr = pvmw.address;
 64		if (pvmw.pte) {
 65			/*
 66			 * For PTE-mapped THP, one sub page is referenced,
 67			 * the whole THP is referenced.
 68			 */
 69			if (ptep_clear_young_notify(vma, addr, pvmw.pte))
 70				referenced = true;
 71		} else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
 72			if (pmdp_clear_young_notify(vma, addr, pvmw.pmd))
 73				referenced = true;
 74		} else {
 75			/* unexpected pmd-mapped page? */
 76			WARN_ON_ONCE(1);
 77		}
 78	}
 79
 80	if (referenced) {
 81		clear_page_idle(page);
 82		/*
 83		 * We cleared the referenced bit in a mapping to this page. To
 84		 * avoid interference with page reclaim, mark it young so that
 85		 * page_referenced() will return > 0.
 86		 */
 87		set_page_young(page);
 88	}
 89	return true;
 90}
 91
 92static void page_idle_clear_pte_refs(struct page *page)
 93{
 94	/*
 95	 * Since rwc.arg is unused, rwc is effectively immutable, so we
 96	 * can make it static const to save some cycles and stack.
 97	 */
 98	static const struct rmap_walk_control rwc = {
 99		.rmap_one = page_idle_clear_pte_refs_one,
100		.anon_lock = page_lock_anon_vma_read,
101	};
102	bool need_lock;
103
104	if (!page_mapped(page) ||
105	    !page_rmapping(page))
106		return;
107
108	need_lock = !PageAnon(page) || PageKsm(page);
109	if (need_lock && !trylock_page(page))
110		return;
111
112	rmap_walk(page, (struct rmap_walk_control *)&rwc);
113
114	if (need_lock)
115		unlock_page(page);
116}
117
118static ssize_t page_idle_bitmap_read(struct file *file, struct kobject *kobj,
119				     struct bin_attribute *attr, char *buf,
120				     loff_t pos, size_t count)
121{
122	u64 *out = (u64 *)buf;
123	struct page *page;
124	unsigned long pfn, end_pfn;
125	int bit;
126
127	if (pos % BITMAP_CHUNK_SIZE || count % BITMAP_CHUNK_SIZE)
128		return -EINVAL;
129
130	pfn = pos * BITS_PER_BYTE;
131	if (pfn >= max_pfn)
132		return 0;
133
134	end_pfn = pfn + count * BITS_PER_BYTE;
135	if (end_pfn > max_pfn)
136		end_pfn = max_pfn;
137
138	for (; pfn < end_pfn; pfn++) {
139		bit = pfn % BITMAP_CHUNK_BITS;
140		if (!bit)
141			*out = 0ULL;
142		page = page_idle_get_page(pfn);
143		if (page) {
144			if (page_is_idle(page)) {
145				/*
146				 * The page might have been referenced via a
147				 * pte, in which case it is not idle. Clear
148				 * refs and recheck.
149				 */
150				page_idle_clear_pte_refs(page);
151				if (page_is_idle(page))
152					*out |= 1ULL << bit;
153			}
154			put_page(page);
155		}
156		if (bit == BITMAP_CHUNK_BITS - 1)
157			out++;
158		cond_resched();
159	}
160	return (char *)out - buf;
161}
162
163static ssize_t page_idle_bitmap_write(struct file *file, struct kobject *kobj,
164				      struct bin_attribute *attr, char *buf,
165				      loff_t pos, size_t count)
166{
167	const u64 *in = (u64 *)buf;
168	struct page *page;
169	unsigned long pfn, end_pfn;
170	int bit;
171
172	if (pos % BITMAP_CHUNK_SIZE || count % BITMAP_CHUNK_SIZE)
173		return -EINVAL;
174
175	pfn = pos * BITS_PER_BYTE;
176	if (pfn >= max_pfn)
177		return -ENXIO;
178
179	end_pfn = pfn + count * BITS_PER_BYTE;
180	if (end_pfn > max_pfn)
181		end_pfn = max_pfn;
182
183	for (; pfn < end_pfn; pfn++) {
184		bit = pfn % BITMAP_CHUNK_BITS;
185		if ((*in >> bit) & 1) {
186			page = page_idle_get_page(pfn);
187			if (page) {
188				page_idle_clear_pte_refs(page);
189				set_page_idle(page);
190				put_page(page);
191			}
192		}
193		if (bit == BITMAP_CHUNK_BITS - 1)
194			in++;
195		cond_resched();
196	}
197	return (char *)in - buf;
198}
199
200static struct bin_attribute page_idle_bitmap_attr =
201		__BIN_ATTR(bitmap, 0600,
202			   page_idle_bitmap_read, page_idle_bitmap_write, 0);
203
204static struct bin_attribute *page_idle_bin_attrs[] = {
205	&page_idle_bitmap_attr,
206	NULL,
207};
208
209static const struct attribute_group page_idle_attr_group = {
210	.bin_attrs = page_idle_bin_attrs,
211	.name = "page_idle",
212};
213
214#ifndef CONFIG_64BIT
215static bool need_page_idle(void)
216{
217	return true;
218}
219struct page_ext_operations page_idle_ops = {
220	.need = need_page_idle,
221};
222#endif
223
224static int __init page_idle_init(void)
225{
226	int err;
227
228	err = sysfs_create_group(mm_kobj, &page_idle_attr_group);
229	if (err) {
230		pr_err("page_idle: register sysfs failed\n");
231		return err;
232	}
233	return 0;
234}
235subsys_initcall(page_idle_init);