mm/page_idle.c

   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  */
  31 static 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
  54 static 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                         referenced = ptep_clear_young_notify(vma, addr,
  69                                         pvmw.pte);
  70                 } else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
  71                         referenced = pmdp_clear_young_notify(vma, addr,
  72                                         pvmw.pmd);
  73                 } else {
  74                         /* unexpected pmd-mapped page? */
  75                         WARN_ON_ONCE(1);
  76                 }
  77         }
  78
  79         if (referenced) {
  80                 clear_page_idle(page);
  81                 /*
  82                  * We cleared the referenced bit in a mapping to this page. To
  83                  * avoid interference with page reclaim, mark it young so that
  84                  * page_referenced() will return > 0.
  85                  */
  86                 set_page_young(page);
  87         }
  88         return true;
  89 }
  90
  91 static void page_idle_clear_pte_refs(struct page *page)
  92 {
  93         /*
  94          * Since rwc.arg is unused, rwc is effectively immutable, so we
  95          * can make it static const to save some cycles and stack.
  96          */
  97         static const struct rmap_walk_control rwc = {
  98                 .rmap_one = page_idle_clear_pte_refs_one,
  99                 .anon_lock = page_lock_anon_vma_read,
 100         };
 101         bool need_lock;
 102
 103         if (!page_mapped(page) ||
 104             !page_rmapping(page))
 105                 return;
 106
 107         need_lock = !PageAnon(page) || PageKsm(page);
 108         if (need_lock && !trylock_page(page))
 109                 return;
 110
 111         rmap_walk(page, (struct rmap_walk_control *)&rwc);
 112
 113         if (need_lock)
 114                 unlock_page(page);
 115 }
 116
 117 static ssize_t page_idle_bitmap_read(struct file *file, struct kobject *kobj,
 118                                      struct bin_attribute *attr, char *buf,
 119                                      loff_t pos, size_t count)
 120 {
 121         u64 *out = (u64 *)buf;
 122         struct page *page;
 123         unsigned long pfn, end_pfn;
 124         int bit;
 125
 126         if (pos % BITMAP_CHUNK_SIZE || count % BITMAP_CHUNK_SIZE)
 127                 return -EINVAL;
 128
 129         pfn = pos * BITS_PER_BYTE;
 130         if (pfn >= max_pfn)
 131                 return 0;
 132
 133         end_pfn = pfn + count * BITS_PER_BYTE;
 134         if (end_pfn > max_pfn)
 135                 end_pfn = ALIGN(max_pfn, BITMAP_CHUNK_BITS);
 136
 137         for (; pfn < end_pfn; pfn++) {
 138                 bit = pfn % BITMAP_CHUNK_BITS;
 139                 if (!bit)
 140                         *out = 0ULL;
 141                 page = page_idle_get_page(pfn);
 142                 if (page) {
 143                         if (page_is_idle(page)) {
 144                                 /*
 145                                  * The page might have been referenced via a
 146                                  * pte, in which case it is not idle. Clear
 147                                  * refs and recheck.
 148                                  */
 149                                 page_idle_clear_pte_refs(page);
 150                                 if (page_is_idle(page))
 151                                         *out |= 1ULL << bit;
 152                         }
 153                         put_page(page);
 154                 }
 155                 if (bit == BITMAP_CHUNK_BITS - 1)
 156                         out++;
 157                 cond_resched();
 158         }
 159         return (char *)out - buf;
 160 }
 161
 162 static ssize_t page_idle_bitmap_write(struct file *file, struct kobject *kobj,
 163                                       struct bin_attribute *attr, char *buf,
 164                                       loff_t pos, size_t count)
 165 {
 166         const u64 *in = (u64 *)buf;
 167         struct page *page;
 168         unsigned long pfn, end_pfn;
 169         int bit;
 170
 171         if (pos % BITMAP_CHUNK_SIZE || count % BITMAP_CHUNK_SIZE)
 172                 return -EINVAL;
 173
 174         pfn = pos * BITS_PER_BYTE;
 175         if (pfn >= max_pfn)
 176                 return -ENXIO;
 177
 178         end_pfn = pfn + count * BITS_PER_BYTE;
 179         if (end_pfn > max_pfn)
 180                 end_pfn = ALIGN(max_pfn, BITMAP_CHUNK_BITS);
 181
 182         for (; pfn < end_pfn; pfn++) {
 183                 bit = pfn % BITMAP_CHUNK_BITS;
 184                 if ((*in >> bit) & 1) {
 185                         page = page_idle_get_page(pfn);
 186                         if (page) {
 187                                 page_idle_clear_pte_refs(page);
 188                                 set_page_idle(page);
 189                                 put_page(page);
 190                         }
 191                 }
 192                 if (bit == BITMAP_CHUNK_BITS - 1)
 193                         in++;
 194                 cond_resched();
 195         }
 196         return (char *)in - buf;
 197 }
 198
 199 static struct bin_attribute page_idle_bitmap_attr =
 200                 __BIN_ATTR(bitmap, S_IRUSR | S_IWUSR,
 201                            page_idle_bitmap_read, page_idle_bitmap_write, 0);
 202
 203 static struct bin_attribute *page_idle_bin_attrs[] = {
 204         &page_idle_bitmap_attr,
 205         NULL,
 206 };
 207
 208 static const struct attribute_group page_idle_attr_group = {
 209         .bin_attrs = page_idle_bin_attrs,
 210         .name = "page_idle",
 211 };
 212
 213 #ifndef CONFIG_64BIT
 214 static bool need_page_idle(void)
 215 {
 216         return true;
 217 }
 218 struct page_ext_operations page_idle_ops = {
 219         .need = need_page_idle,
 220 };
 221 #endif
 222
 223 static int __init page_idle_init(void)
 224 {
 225         int err;
 226
 227         err = sysfs_create_group(mm_kobj, &page_idle_attr_group);
 228         if (err) {
 229                 pr_err("page_idle: register sysfs failed\n");
 230                 return err;
 231         }
 232         return 0;
 233 }
 234 subsys_initcall(page_idle_init);