xref: /openbmc/linux/mm/page_idle.c (revision 5acc17fd)
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  */
page_idle_get_folio(unsigned long pfn)34 static 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 
page_idle_clear_pte_refs_one(struct folio * folio,struct vm_area_struct * vma,unsigned long addr,void * arg)52 static 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 
page_idle_clear_pte_refs(struct folio * folio)89 static 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 
page_idle_bitmap_read(struct file * file,struct kobject * kobj,struct bin_attribute * attr,char * buf,loff_t pos,size_t count)114 static 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 
page_idle_bitmap_write(struct file * file,struct kobject * kobj,struct bin_attribute * attr,char * buf,loff_t pos,size_t count)159 static 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 
196 static struct bin_attribute page_idle_bitmap_attr =
197 		__BIN_ATTR(bitmap, 0600,
198 			   page_idle_bitmap_read, page_idle_bitmap_write, 0);
199 
200 static struct bin_attribute *page_idle_bin_attrs[] = {
201 	&page_idle_bitmap_attr,
202 	NULL,
203 };
204 
205 static const struct attribute_group page_idle_attr_group = {
206 	.bin_attrs = page_idle_bin_attrs,
207 	.name = "page_idle",
208 };
209 
page_idle_init(void)210 static 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 }
221 subsys_initcall(page_idle_init);
222