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                         /*
  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
  95 static 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
 121 static 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
 166 static 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
 203 static struct bin_attribute page_idle_bitmap_attr =
 204                 __BIN_ATTR(bitmap, 0600,
 205                            page_idle_bitmap_read, page_idle_bitmap_write, 0);
 206
 207 static struct bin_attribute *page_idle_bin_attrs[] = {
 208         &page_idle_bitmap_attr,
 209         NULL,
 210 };
 211
 212 static 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
 218 static bool need_page_idle(void)
 219 {
 220         return true;
 221 }
 222 struct page_ext_operations page_idle_ops = {
 223         .need = need_page_idle,
 224 };
 225 #endif
 226
 227 static 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 }
 238 subsys_initcall(page_idle_init);