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 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
  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
  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
 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
 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
 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);