mm/page_idle.c

   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  */
  32 static struct page *page_idle_get_page(unsigned long pfn)
  33 {
  34         struct page *page = pfn_to_online_page(pfn);
  35         pg_data_t *pgdat;
  36
  37         if (!page || !PageLRU(page) ||
  38             !get_page_unless_zero(page))
  39                 return NULL;
  40
  41         pgdat = page_pgdat(page);
  42         spin_lock_irq(&pgdat->lru_lock);
  43         if (unlikely(!PageLRU(page))) {
  44                 put_page(page);
  45                 page = NULL;
  46         }
  47         spin_unlock_irq(&pgdat->lru_lock);
  48         return page;
  49 }
  50
  51 static bool page_idle_clear_pte_refs_one(struct page *page,
  52                                         struct vm_area_struct *vma,
  53                                         unsigned long addr, void *arg)
  54 {
  55         struct page_vma_mapped_walk pvmw = {
  56                 .page = page,
  57                 .vma = vma,
  58                 .address = addr,
  59         };
  60         bool referenced = false;
  61
  62         while (page_vma_mapped_walk(&pvmw)) {
  63                 addr = pvmw.address;
  64                 if (pvmw.pte) {
  65                         /*
  66                          * For PTE-mapped THP, one sub page is referenced,
  67                          * the whole THP is referenced.
  68                          */
  69                         if (ptep_clear_young_notify(vma, addr, pvmw.pte))
  70                                 referenced = true;
  71                 } else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
  72                         if (pmdp_clear_young_notify(vma, addr, pvmw.pmd))
  73                                 referenced = true;
  74                 } else {
  75                         /* unexpected pmd-mapped page? */
  76                         WARN_ON_ONCE(1);
  77                 }
  78         }
  79
  80         if (referenced) {
  81                 clear_page_idle(page);
  82                 /*
  83                  * We cleared the referenced bit in a mapping to this page. To
  84                  * avoid interference with page reclaim, mark it young so that
  85                  * page_referenced() will return > 0.
  86                  */
  87                 set_page_young(page);
  88         }
  89         return true;
  90 }
  91
  92 static void page_idle_clear_pte_refs(struct page *page)
  93 {
  94         /*
  95          * Since rwc.arg is unused, rwc is effectively immutable, so we
  96          * can make it static const to save some cycles and stack.
  97          */
  98         static const struct rmap_walk_control rwc = {
  99                 .rmap_one = page_idle_clear_pte_refs_one,
 100                 .anon_lock = page_lock_anon_vma_read,
 101         };
 102         bool need_lock;
 103
 104         if (!page_mapped(page) ||
 105             !page_rmapping(page))
 106                 return;
 107
 108         need_lock = !PageAnon(page) || PageKsm(page);
 109         if (need_lock && !trylock_page(page))
 110                 return;
 111
 112         rmap_walk(page, (struct rmap_walk_control *)&rwc);
 113
 114         if (need_lock)
 115                 unlock_page(page);
 116 }
 117
 118 static ssize_t page_idle_bitmap_read(struct file *file, struct kobject *kobj,
 119                                      struct bin_attribute *attr, char *buf,
 120                                      loff_t pos, size_t count)
 121 {
 122         u64 *out = (u64 *)buf;
 123         struct page *page;
 124         unsigned long pfn, end_pfn;
 125         int bit;
 126
 127         if (pos % BITMAP_CHUNK_SIZE || count % BITMAP_CHUNK_SIZE)
 128                 return -EINVAL;
 129
 130         pfn = pos * BITS_PER_BYTE;
 131         if (pfn >= max_pfn)
 132                 return 0;
 133
 134         end_pfn = pfn + count * BITS_PER_BYTE;
 135         if (end_pfn > max_pfn)
 136                 end_pfn = max_pfn;
 137
 138         for (; pfn < end_pfn; pfn++) {
 139                 bit = pfn % BITMAP_CHUNK_BITS;
 140                 if (!bit)
 141                         *out = 0ULL;
 142                 page = page_idle_get_page(pfn);
 143                 if (page) {
 144                         if (page_is_idle(page)) {
 145                                 /*
 146                                  * The page might have been referenced via a
 147                                  * pte, in which case it is not idle. Clear
 148                                  * refs and recheck.
 149                                  */
 150                                 page_idle_clear_pte_refs(page);
 151                                 if (page_is_idle(page))
 152                                         *out |= 1ULL << bit;
 153                         }
 154                         put_page(page);
 155                 }
 156                 if (bit == BITMAP_CHUNK_BITS - 1)
 157                         out++;
 158                 cond_resched();
 159         }
 160         return (char *)out - buf;
 161 }
 162
 163 static ssize_t page_idle_bitmap_write(struct file *file, struct kobject *kobj,
 164                                       struct bin_attribute *attr, char *buf,
 165                                       loff_t pos, size_t count)
 166 {
 167         const u64 *in = (u64 *)buf;
 168         struct page *page;
 169         unsigned long pfn, end_pfn;
 170         int bit;
 171
 172         if (pos % BITMAP_CHUNK_SIZE || count % BITMAP_CHUNK_SIZE)
 173                 return -EINVAL;
 174
 175         pfn = pos * BITS_PER_BYTE;
 176         if (pfn >= max_pfn)
 177                 return -ENXIO;
 178
 179         end_pfn = pfn + count * BITS_PER_BYTE;
 180         if (end_pfn > max_pfn)
 181                 end_pfn = max_pfn;
 182
 183         for (; pfn < end_pfn; pfn++) {
 184                 bit = pfn % BITMAP_CHUNK_BITS;
 185                 if ((*in >> bit) & 1) {
 186                         page = page_idle_get_page(pfn);
 187                         if (page) {
 188                                 page_idle_clear_pte_refs(page);
 189                                 set_page_idle(page);
 190                                 put_page(page);
 191                         }
 192                 }
 193                 if (bit == BITMAP_CHUNK_BITS - 1)
 194                         in++;
 195                 cond_resched();
 196         }
 197         return (char *)in - buf;
 198 }
 199
 200 static struct bin_attribute page_idle_bitmap_attr =
 201                 __BIN_ATTR(bitmap, 0600,
 202                            page_idle_bitmap_read, page_idle_bitmap_write, 0);
 203
 204 static struct bin_attribute *page_idle_bin_attrs[] = {
 205         &page_idle_bitmap_attr,
 206         NULL,
 207 };
 208
 209 static const struct attribute_group page_idle_attr_group = {
 210         .bin_attrs = page_idle_bin_attrs,
 211         .name = "page_idle",
 212 };
 213
 214 #ifndef CONFIG_64BIT
 215 static bool need_page_idle(void)
 216 {
 217         return true;
 218 }
 219 struct page_ext_operations page_idle_ops = {
 220         .need = need_page_idle,
 221 };
 222 #endif
 223
 224 static int __init page_idle_init(void)
 225 {
 226         int err;
 227
 228         err = sysfs_create_group(mm_kobj, &page_idle_attr_group);
 229         if (err) {
 230                 pr_err("page_idle: register sysfs failed\n");
 231                 return err;
 232         }
 233         return 0;
 234 }
 235 subsys_initcall(page_idle_init);