1// SPDX-License-Identifier: GPL-2.0
  2#include <linux/init.h>
  3#include <linux/bootmem.h>
  4#include <linux/fs.h>
  5#include <linux/sysfs.h>
  6#include <linux/kobject.h>
  7#include <linux/mm.h>
  8#include <linux/mmzone.h>
  9#include <linux/pagemap.h>
 10#include <linux/rmap.h>
 11#include <linux/mmu_notifier.h>
 12#include <linux/page_ext.h>
 13#include <linux/page_idle.h>
 14
 15#define BITMAP_CHUNK_SIZE	sizeof(u64)
 16#define BITMAP_CHUNK_BITS	(BITMAP_CHUNK_SIZE * BITS_PER_BYTE)
 17
 18/*
 19 * Idle page tracking only considers user memory pages, for other types of
 20 * pages the idle flag is always unset and an attempt to set it is silently
 21 * ignored.
 22 *
 23 * We treat a page as a user memory page if it is on an LRU list, because it is
 24 * always safe to pass such a page to rmap_walk(), which is essential for idle
 25 * page tracking. With such an indicator of user pages we can skip isolated
 26 * pages, but since there are not usually many of them, it will hardly affect
 27 * the overall result.
 28 *
 29 * This function tries to get a user memory page by pfn as described above.
 30 */
 31static struct page *page_idle_get_page(unsigned long pfn)
 32{
 33	struct page *page;
 34	struct zone *zone;
 35
 36	if (!pfn_valid(pfn))
 37		return NULL;
 38
 39	page = pfn_to_page(pfn);
 40	if (!page || !PageLRU(page) ||
 41	    !get_page_unless_zero(page))
 42		return NULL;
 43
 44	zone = page_zone(page);
 45	spin_lock_irq(zone_lru_lock(zone));
 46	if (unlikely(!PageLRU(page))) {
 47		put_page(page);
 48		page = NULL;
 49	}
 50	spin_unlock_irq(zone_lru_lock(zone));
 51	return page;
 52}
 53
 54static bool page_idle_clear_pte_refs_one(struct page *page,
 55					struct vm_area_struct *vma,
 56					unsigned long addr, void *arg)
 57{
 58	struct page_vma_mapped_walk pvmw = {
 59		.page = page,
 60		.vma = vma,
 61		.address = addr,
 62	};
 63	bool referenced = false;
 64
 65	while (page_vma_mapped_walk(&pvmw)) {
 66		addr = pvmw.address;
 67		if (pvmw.pte) {
 68			/*
 69			 * For PTE-mapped THP, one sub page is referenced,
 70			 * the whole THP is referenced.
 71			 */
 72			if (ptep_clear_young_notify(vma, addr, pvmw.pte))
 73				referenced = true;
 74		} else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
 75			if (pmdp_clear_young_notify(vma, addr, pvmw.pmd))
 76				referenced = true;
 77		} else {
 78			/* unexpected pmd-mapped page? */
 79			WARN_ON_ONCE(1);
 80		}
 81	}
 82
 83	if (referenced) {
 84		clear_page_idle(page);
 85		/*
 86		 * We cleared the referenced bit in a mapping to this page. To
 87		 * avoid interference with page reclaim, mark it young so that
 88		 * page_referenced() will return > 0.
 89		 */
 90		set_page_young(page);
 91	}
 92	return true;
 93}
 94
 95static void page_idle_clear_pte_refs(struct page *page)
 96{
 97	/*
 98	 * Since rwc.arg is unused, rwc is effectively immutable, so we
 99	 * can make it static const to save some cycles and stack.
100	 */
101	static const struct rmap_walk_control rwc = {
102		.rmap_one = page_idle_clear_pte_refs_one,
103		.anon_lock = page_lock_anon_vma_read,
104	};
105	bool need_lock;
106
107	if (!page_mapped(page) ||
108	    !page_rmapping(page))
109		return;
110
111	need_lock = !PageAnon(page) || PageKsm(page);
112	if (need_lock && !trylock_page(page))
113		return;
114
115	rmap_walk(page, (struct rmap_walk_control *)&rwc);
116
117	if (need_lock)
118		unlock_page(page);
119}
120
121static ssize_t page_idle_bitmap_read(struct file *file, struct kobject *kobj,
122				     struct bin_attribute *attr, char *buf,
123				     loff_t pos, size_t count)
124{
125	u64 *out = (u64 *)buf;
126	struct page *page;
127	unsigned long pfn, end_pfn;
128	int bit;
129
130	if (pos % BITMAP_CHUNK_SIZE || count % BITMAP_CHUNK_SIZE)
131		return -EINVAL;
132
133	pfn = pos * BITS_PER_BYTE;
134	if (pfn >= max_pfn)
135		return 0;
136
137	end_pfn = pfn + count * BITS_PER_BYTE;
138	if (end_pfn > max_pfn)
139		end_pfn = ALIGN(max_pfn, BITMAP_CHUNK_BITS);
140
141	for (; pfn < end_pfn; pfn++) {
142		bit = pfn % BITMAP_CHUNK_BITS;
143		if (!bit)
144			*out = 0ULL;
145		page = page_idle_get_page(pfn);
146		if (page) {
147			if (page_is_idle(page)) {
148				/*
149				 * The page might have been referenced via a
150				 * pte, in which case it is not idle. Clear
151				 * refs and recheck.
152				 */
153				page_idle_clear_pte_refs(page);
154				if (page_is_idle(page))
155					*out |= 1ULL << bit;
156			}
157			put_page(page);
158		}
159		if (bit == BITMAP_CHUNK_BITS - 1)
160			out++;
161		cond_resched();
162	}
163	return (char *)out - buf;
164}
165
166static ssize_t page_idle_bitmap_write(struct file *file, struct kobject *kobj,
167				      struct bin_attribute *attr, char *buf,
168				      loff_t pos, size_t count)
169{
170	const u64 *in = (u64 *)buf;
171	struct page *page;
172	unsigned long pfn, end_pfn;
173	int bit;
174
175	if (pos % BITMAP_CHUNK_SIZE || count % BITMAP_CHUNK_SIZE)
176		return -EINVAL;
177
178	pfn = pos * BITS_PER_BYTE;
179	if (pfn >= max_pfn)
180		return -ENXIO;
181
182	end_pfn = pfn + count * BITS_PER_BYTE;
183	if (end_pfn > max_pfn)
184		end_pfn = ALIGN(max_pfn, BITMAP_CHUNK_BITS);
185
186	for (; pfn < end_pfn; pfn++) {
187		bit = pfn % BITMAP_CHUNK_BITS;
188		if ((*in >> bit) & 1) {
189			page = page_idle_get_page(pfn);
190			if (page) {
191				page_idle_clear_pte_refs(page);
192				set_page_idle(page);
193				put_page(page);
194			}
195		}
196		if (bit == BITMAP_CHUNK_BITS - 1)
197			in++;
198		cond_resched();
199	}
200	return (char *)in - buf;
201}
202
203static struct bin_attribute page_idle_bitmap_attr =
204		__BIN_ATTR(bitmap, S_IRUSR | S_IWUSR,
205			   page_idle_bitmap_read, page_idle_bitmap_write, 0);
206
207static struct bin_attribute *page_idle_bin_attrs[] = {
208	&page_idle_bitmap_attr,
209	NULL,
210};
211
212static const struct attribute_group page_idle_attr_group = {
213	.bin_attrs = page_idle_bin_attrs,
214	.name = "page_idle",
215};
216
217#ifndef CONFIG_64BIT
218static bool need_page_idle(void)
219{
220	return true;
221}
222struct page_ext_operations page_idle_ops = {
223	.need = need_page_idle,
224};
225#endif
226
227static int __init page_idle_init(void)
228{
229	int err;
230
231	err = sysfs_create_group(mm_kobj, &page_idle_attr_group);
232	if (err) {
233		pr_err("page_idle: register sysfs failed\n");
234		return err;
235	}
236	return 0;
237}
238subsys_initcall(page_idle_init);