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 page *page_idle_get_page(unsigned long pfn)
 35{
 36	struct page *page = pfn_to_online_page(pfn);
 37
 38	if (!page || !PageLRU(page) ||
 39	    !get_page_unless_zero(page))
 40		return NULL;
 41
 42	if (unlikely(!PageLRU(page))) {
 43		put_page(page);
 44		page = NULL;
 45	}
 46	return page;
 47}
 48
 49static bool page_idle_clear_pte_refs_one(struct folio *folio,
 50					struct vm_area_struct *vma,
 51					unsigned long addr, void *arg)
 52{
 53	DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, addr, 0);
 54	bool referenced = false;
 55
 56	while (page_vma_mapped_walk(&pvmw)) {
 57		addr = pvmw.address;
 58		if (pvmw.pte) {
 59			/*
 60			 * For PTE-mapped THP, one sub page is referenced,
 61			 * the whole THP is referenced.
 62			 */
 63			if (ptep_clear_young_notify(vma, addr, pvmw.pte))
 64				referenced = true;
 65		} else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
 66			if (pmdp_clear_young_notify(vma, addr, pvmw.pmd))
 67				referenced = true;
 68		} else {
 69			/* unexpected pmd-mapped page? */
 70			WARN_ON_ONCE(1);
 71		}
 72	}
 73
 74	if (referenced) {
 75		folio_clear_idle(folio);
 76		/*
 77		 * We cleared the referenced bit in a mapping to this page. To
 78		 * avoid interference with page reclaim, mark it young so that
 79		 * folio_referenced() will return > 0.
 80		 */
 81		folio_set_young(folio);
 82	}
 83	return true;
 84}
 85
 86static void page_idle_clear_pte_refs(struct page *page)
 87{
 88	struct folio *folio = page_folio(page);
 89
 90	/*
 91	 * Since rwc.try_lock is unused, rwc is effectively immutable, so we
 92	 * can make it static to save some cycles and stack.
 93	 */
 94	static struct rmap_walk_control rwc = {
 95		.rmap_one = page_idle_clear_pte_refs_one,
 96		.anon_lock = folio_lock_anon_vma_read,
 97	};
 98	bool need_lock;
 99
100	if (!folio_mapped(folio) || !folio_raw_mapping(folio))
101		return;
102
103	need_lock = !folio_test_anon(folio) || folio_test_ksm(folio);
104	if (need_lock && !folio_trylock(folio))
105		return;
106
107	rmap_walk(folio, &rwc);
108
109	if (need_lock)
110		folio_unlock(folio);
111}
112
113static ssize_t page_idle_bitmap_read(struct file *file, struct kobject *kobj,
114				     struct bin_attribute *attr, char *buf,
115				     loff_t pos, size_t count)
116{
117	u64 *out = (u64 *)buf;
118	struct page *page;
119	unsigned long pfn, end_pfn;
120	int bit;
121
122	if (pos % BITMAP_CHUNK_SIZE || count % BITMAP_CHUNK_SIZE)
123		return -EINVAL;
124
125	pfn = pos * BITS_PER_BYTE;
126	if (pfn >= max_pfn)
127		return 0;
128
129	end_pfn = pfn + count * BITS_PER_BYTE;
130	if (end_pfn > max_pfn)
131		end_pfn = max_pfn;
132
133	for (; pfn < end_pfn; pfn++) {
134		bit = pfn % BITMAP_CHUNK_BITS;
135		if (!bit)
136			*out = 0ULL;
137		page = page_idle_get_page(pfn);
138		if (page) {
139			if (page_is_idle(page)) {
140				/*
141				 * The page might have been referenced via a
142				 * pte, in which case it is not idle. Clear
143				 * refs and recheck.
144				 */
145				page_idle_clear_pte_refs(page);
146				if (page_is_idle(page))
147					*out |= 1ULL << bit;
148			}
149			put_page(page);
150		}
151		if (bit == BITMAP_CHUNK_BITS - 1)
152			out++;
153		cond_resched();
154	}
155	return (char *)out - buf;
156}
157
158static ssize_t page_idle_bitmap_write(struct file *file, struct kobject *kobj,
159				      struct bin_attribute *attr, char *buf,
160				      loff_t pos, size_t count)
161{
162	const u64 *in = (u64 *)buf;
163	struct page *page;
164	unsigned long pfn, end_pfn;
165	int bit;
166
167	if (pos % BITMAP_CHUNK_SIZE || count % BITMAP_CHUNK_SIZE)
168		return -EINVAL;
169
170	pfn = pos * BITS_PER_BYTE;
171	if (pfn >= max_pfn)
172		return -ENXIO;
173
174	end_pfn = pfn + count * BITS_PER_BYTE;
175	if (end_pfn > max_pfn)
176		end_pfn = max_pfn;
177
178	for (; pfn < end_pfn; pfn++) {
179		bit = pfn % BITMAP_CHUNK_BITS;
180		if ((*in >> bit) & 1) {
181			page = page_idle_get_page(pfn);
182			if (page) {
183				page_idle_clear_pte_refs(page);
184				set_page_idle(page);
185				put_page(page);
186			}
187		}
188		if (bit == BITMAP_CHUNK_BITS - 1)
189			in++;
190		cond_resched();
191	}
192	return (char *)in - buf;
193}
194
195static struct bin_attribute page_idle_bitmap_attr =
196		__BIN_ATTR(bitmap, 0600,
197			   page_idle_bitmap_read, page_idle_bitmap_write, 0);
198
199static struct bin_attribute *page_idle_bin_attrs[] = {
200	&page_idle_bitmap_attr,
201	NULL,
202};
203
204static const struct attribute_group page_idle_attr_group = {
205	.bin_attrs = page_idle_bin_attrs,
206	.name = "page_idle",
207};
208
209static int __init page_idle_init(void)
210{
211	int err;
212
213	err = sysfs_create_group(mm_kobj, &page_idle_attr_group);
214	if (err) {
215		pr_err("page_idle: register sysfs failed\n");
216		return err;
217	}
218	return 0;
219}
220subsys_initcall(page_idle_init);