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 #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  */
  34 static 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
  49 static 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
  86 static 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
 113 static 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
 158 static 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
 195 static struct bin_attribute page_idle_bitmap_attr =
 196                 __BIN_ATTR(bitmap, 0600,
 197                            page_idle_bitmap_read, page_idle_bitmap_write, 0);
 198
 199 static struct bin_attribute *page_idle_bin_attrs[] = {
 200         &page_idle_bitmap_attr,
 201         NULL,
 202 };
 203
 204 static const struct attribute_group page_idle_attr_group = {
 205         .bin_attrs = page_idle_bin_attrs,
 206         .name = "page_idle",
 207 };
 208
 209 static 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 }
 220 subsys_initcall(page_idle_init);