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
 36	if (!page || !PageLRU(page) ||
 37	    !get_page_unless_zero(page))
 38		return NULL;
 39
 40	if (unlikely(!PageLRU(page))) {
 41		put_page(page);
 42		page = NULL;
 43	}
 44	return page;
 45}
 46
 47static bool page_idle_clear_pte_refs_one(struct page *page,
 48					struct vm_area_struct *vma,
 49					unsigned long addr, void *arg)
 50{
 51	struct page_vma_mapped_walk pvmw = {
 52		.page = page,
 53		.vma = vma,
 54		.address = addr,
 55	};
 56	bool referenced = false;
 57
 58	while (page_vma_mapped_walk(&pvmw)) {
 59		addr = pvmw.address;
 60		if (pvmw.pte) {
 61			/*
 62			 * For PTE-mapped THP, one sub page is referenced,
 63			 * the whole THP is referenced.
 64			 */
 65			if (ptep_clear_young_notify(vma, addr, pvmw.pte))
 66				referenced = true;
 67		} else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
 68			if (pmdp_clear_young_notify(vma, addr, pvmw.pmd))
 69				referenced = true;
 70		} else {
 71			/* unexpected pmd-mapped page? */
 72			WARN_ON_ONCE(1);
 73		}
 74	}
 75
 76	if (referenced) {
 77		clear_page_idle(page);
 78		/*
 79		 * We cleared the referenced bit in a mapping to this page. To
 80		 * avoid interference with page reclaim, mark it young so that
 81		 * page_referenced() will return > 0.
 82		 */
 83		set_page_young(page);
 84	}
 85	return true;
 86}
 87
 88static void page_idle_clear_pte_refs(struct page *page)
 89{
 90	/*
 91	 * Since rwc.arg is unused, rwc is effectively immutable, so we
 92	 * can make it static const to save some cycles and stack.
 93	 */
 94	static const struct rmap_walk_control rwc = {
 95		.rmap_one = page_idle_clear_pte_refs_one,
 96		.anon_lock = page_lock_anon_vma_read,
 97	};
 98	bool need_lock;
 99
100	if (!page_mapped(page) ||
101	    !page_rmapping(page))
102		return;
103
104	need_lock = !PageAnon(page) || PageKsm(page);
105	if (need_lock && !trylock_page(page))
106		return;
107
108	rmap_walk(page, (struct rmap_walk_control *)&rwc);
109
110	if (need_lock)
111		unlock_page(page);
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 page *page;
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		page = page_idle_get_page(pfn);
139		if (page) {
140			if (page_is_idle(page)) {
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(page);
147				if (page_is_idle(page))
148					*out |= 1ULL << bit;
149			}
150			put_page(page);
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 page *page;
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			page = page_idle_get_page(pfn);
183			if (page) {
184				page_idle_clear_pte_refs(page);
185				set_page_idle(page);
186				put_page(page);
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
210#ifndef CONFIG_64BIT
211static bool need_page_idle(void)
212{
213	return true;
214}
215struct page_ext_operations page_idle_ops = {
216	.need = need_page_idle,
217};
218#endif
219
220static int __init page_idle_init(void)
221{
222	int err;
223
224	err = sysfs_create_group(mm_kobj, &page_idle_attr_group);
225	if (err) {
226		pr_err("page_idle: register sysfs failed\n");
227		return err;
228	}
229	return 0;
230}
231subsys_initcall(page_idle_init);