mm/page_idle.c

   1 #include <linux/init.h>
   2 #include <linux/bootmem.h>
   3 #include <linux/fs.h>
   4 #include <linux/sysfs.h>
   5 #include <linux/kobject.h>
   6 #include <linux/mm.h>
   7 #include <linux/mmzone.h>
   8 #include <linux/pagemap.h>
   9 #include <linux/rmap.h>
  10 #include <linux/mmu_notifier.h>
  11 #include <linux/page_ext.h>
  12 #include <linux/page_idle.h>
  13
  14 #define BITMAP_CHUNK_SIZE       sizeof(u64)
  15 #define BITMAP_CHUNK_BITS       (BITMAP_CHUNK_SIZE * BITS_PER_BYTE)
  16
  17 /*
  18  * Idle page tracking only considers user memory pages, for other types of
  19  * pages the idle flag is always unset and an attempt to set it is silently
  20  * ignored.
  21  *
  22  * We treat a page as a user memory page if it is on an LRU list, because it is
  23  * always safe to pass such a page to rmap_walk(), which is essential for idle
  24  * page tracking. With such an indicator of user pages we can skip isolated
  25  * pages, but since there are not usually many of them, it will hardly affect
  26  * the overall result.
  27  *
  28  * This function tries to get a user memory page by pfn as described above.
  29  */
  30 static struct page *page_idle_get_page(unsigned long pfn)
  31 {
  32         struct page *page;
  33         struct zone *zone;
  34
  35         if (!pfn_valid(pfn))
  36                 return NULL;
  37
  38         page = pfn_to_page(pfn);
  39         if (!page || !PageLRU(page) ||
  40             !get_page_unless_zero(page))
  41                 return NULL;
  42
  43         zone = page_zone(page);
  44         spin_lock_irq(zone_lru_lock(zone));
  45         if (unlikely(!PageLRU(page))) {
  46                 put_page(page);
  47                 page = NULL;
  48         }
  49         spin_unlock_irq(zone_lru_lock(zone));
  50         return page;
  51 }
  52
  53 static int page_idle_clear_pte_refs_one(struct page *page,
  54                                         struct vm_area_struct *vma,
  55                                         unsigned long addr, void *arg)
  56 {
  57         struct mm_struct *mm = vma->vm_mm;
  58         pmd_t *pmd;
  59         pte_t *pte;
  60         spinlock_t *ptl;
  61         bool referenced = false;
  62
  63         if (!page_check_address_transhuge(page, mm, addr, &pmd, &pte, &ptl))
  64                 return SWAP_AGAIN;
  65
  66         if (pte) {
  67                 referenced = ptep_clear_young_notify(vma, addr, pte);
  68                 pte_unmap(pte);
  69         } else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) {
  70                 referenced = pmdp_clear_young_notify(vma, addr, pmd);
  71         } else {
  72                 /* unexpected pmd-mapped page? */
  73                 WARN_ON_ONCE(1);
  74         }
  75
  76         spin_unlock(ptl);
  77
  78         if (referenced) {
  79                 clear_page_idle(page);
  80                 /*
  81                  * We cleared the referenced bit in a mapping to this page. To
  82                  * avoid interference with page reclaim, mark it young so that
  83                  * page_referenced() will return > 0.
  84                  */
  85                 set_page_young(page);
  86         }
  87         return SWAP_AGAIN;
  88 }
  89
  90 static void page_idle_clear_pte_refs(struct page *page)
  91 {
  92         /*
  93          * Since rwc.arg is unused, rwc is effectively immutable, so we
  94          * can make it static const to save some cycles and stack.
  95          */
  96         static const struct rmap_walk_control rwc = {
  97                 .rmap_one = page_idle_clear_pte_refs_one,
  98                 .anon_lock = page_lock_anon_vma_read,
  99         };
 100         bool need_lock;
 101
 102         if (!page_mapped(page) ||
 103             !page_rmapping(page))
 104                 return;
 105
 106         need_lock = !PageAnon(page) || PageKsm(page);
 107         if (need_lock && !trylock_page(page))
 108                 return;
 109
 110         rmap_walk(page, (struct rmap_walk_control *)&rwc);
 111
 112         if (need_lock)
 113                 unlock_page(page);
 114 }
 115
 116 static ssize_t page_idle_bitmap_read(struct file *file, struct kobject *kobj,
 117                                      struct bin_attribute *attr, char *buf,
 118                                      loff_t pos, size_t count)
 119 {
 120         u64 *out = (u64 *)buf;
 121         struct page *page;
 122         unsigned long pfn, end_pfn;
 123         int bit;
 124
 125         if (pos % BITMAP_CHUNK_SIZE || count % BITMAP_CHUNK_SIZE)
 126                 return -EINVAL;
 127
 128         pfn = pos * BITS_PER_BYTE;
 129         if (pfn >= max_pfn)
 130                 return 0;
 131
 132         end_pfn = pfn + count * BITS_PER_BYTE;
 133         if (end_pfn > max_pfn)
 134                 end_pfn = ALIGN(max_pfn, BITMAP_CHUNK_BITS);
 135
 136         for (; pfn < end_pfn; pfn++) {
 137                 bit = pfn % BITMAP_CHUNK_BITS;
 138                 if (!bit)
 139                         *out = 0ULL;
 140                 page = page_idle_get_page(pfn);
 141                 if (page) {
 142                         if (page_is_idle(page)) {
 143                                 /*
 144                                  * The page might have been referenced via a
 145                                  * pte, in which case it is not idle. Clear
 146                                  * refs and recheck.
 147                                  */
 148                                 page_idle_clear_pte_refs(page);
 149                                 if (page_is_idle(page))
 150                                         *out |= 1ULL << bit;
 151                         }
 152                         put_page(page);
 153                 }
 154                 if (bit == BITMAP_CHUNK_BITS - 1)
 155                         out++;
 156                 cond_resched();
 157         }
 158         return (char *)out - buf;
 159 }
 160
 161 static ssize_t page_idle_bitmap_write(struct file *file, struct kobject *kobj,
 162                                       struct bin_attribute *attr, char *buf,
 163                                       loff_t pos, size_t count)
 164 {
 165         const u64 *in = (u64 *)buf;
 166         struct page *page;
 167         unsigned long pfn, end_pfn;
 168         int bit;
 169
 170         if (pos % BITMAP_CHUNK_SIZE || count % BITMAP_CHUNK_SIZE)
 171                 return -EINVAL;
 172
 173         pfn = pos * BITS_PER_BYTE;
 174         if (pfn >= max_pfn)
 175                 return -ENXIO;
 176
 177         end_pfn = pfn + count * BITS_PER_BYTE;
 178         if (end_pfn > max_pfn)
 179                 end_pfn = ALIGN(max_pfn, BITMAP_CHUNK_BITS);
 180
 181         for (; pfn < end_pfn; pfn++) {
 182                 bit = pfn % BITMAP_CHUNK_BITS;
 183                 if ((*in >> bit) & 1) {
 184                         page = page_idle_get_page(pfn);
 185                         if (page) {
 186                                 page_idle_clear_pte_refs(page);
 187                                 set_page_idle(page);
 188                                 put_page(page);
 189                         }
 190                 }
 191                 if (bit == BITMAP_CHUNK_BITS - 1)
 192                         in++;
 193                 cond_resched();
 194         }
 195         return (char *)in - buf;
 196 }
 197
 198 static struct bin_attribute page_idle_bitmap_attr =
 199                 __BIN_ATTR(bitmap, S_IRUSR | S_IWUSR,
 200                            page_idle_bitmap_read, page_idle_bitmap_write, 0);
 201
 202 static struct bin_attribute *page_idle_bin_attrs[] = {
 203         &page_idle_bitmap_attr,
 204         NULL,
 205 };
 206
 207 static struct attribute_group page_idle_attr_group = {
 208         .bin_attrs = page_idle_bin_attrs,
 209         .name = "page_idle",
 210 };
 211
 212 #ifndef CONFIG_64BIT
 213 static bool need_page_idle(void)
 214 {
 215         return true;
 216 }
 217 struct page_ext_operations page_idle_ops = {
 218         .need = need_page_idle,
 219 };
 220 #endif
 221
 222 static int __init page_idle_init(void)
 223 {
 224         int err;
 225
 226         err = sysfs_create_group(mm_kobj, &page_idle_attr_group);
 227         if (err) {
 228                 pr_err("page_idle: register sysfs failed\n");
 229                 return err;
 230         }
 231         return 0;
 232 }
 233 subsys_initcall(page_idle_init);