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);
  45         if (unlikely(!PageLRU(page))) {
  46                 put_page(page);
  47                 page = NULL;
  48         }
  49         spin_unlock_irq(&zone->lru_lock);
  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         spinlock_t *ptl;
  59         pmd_t *pmd;
  60         pte_t *pte;
  61         bool referenced = false;
  62
  63         if (unlikely(PageTransHuge(page))) {
  64                 pmd = page_check_address_pmd(page, mm, addr, &ptl);
  65                 if (pmd) {
  66                         referenced = pmdp_clear_young_notify(vma, addr, pmd);
  67                         spin_unlock(ptl);
  68                 }
  69         } else {
  70                 pte = page_check_address(page, mm, addr, &ptl, 0);
  71                 if (pte) {
  72                         referenced = ptep_clear_young_notify(vma, addr, pte);
  73                         pte_unmap_unlock(pte, ptl);
  74                 }
  75         }
  76         if (referenced) {
  77                 clear_page_idle(page);
  78                 /*
  79                  * We cleared the referenced bit in a mapping to this page. To
  80                  * avoid interference with page reclaim, mark it young so that
  81                  * page_referenced() will return > 0.
  82                  */
  83                 set_page_young(page);
  84         }
  85         return SWAP_AGAIN;
  86 }
  87
  88 static void page_idle_clear_pte_refs(struct page *page)
  89 {
  90         /*
  91          * Since rwc.arg is unused, rwc is effectively immutable, so we
  92          * can make it static const to save some cycles and stack.
  93          */
  94         static const struct rmap_walk_control rwc = {
  95                 .rmap_one = page_idle_clear_pte_refs_one,
  96                 .anon_lock = page_lock_anon_vma_read,
  97         };
  98         bool need_lock;
  99
 100         if (!page_mapped(page) ||
 101             !page_rmapping(page))
 102                 return;
 103
 104         need_lock = !PageAnon(page) || PageKsm(page);
 105         if (need_lock && !trylock_page(page))
 106                 return;
 107
 108         rmap_walk(page, (struct rmap_walk_control *)&rwc);
 109
 110         if (need_lock)
 111                 unlock_page(page);
 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 page *page;
 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 = ALIGN(max_pfn, BITMAP_CHUNK_BITS);
 133
 134         for (; pfn < end_pfn; pfn++) {
 135                 bit = pfn % BITMAP_CHUNK_BITS;
 136                 if (!bit)
 137                         *out = 0ULL;
 138                 page = page_idle_get_page(pfn);
 139                 if (page) {
 140                         if (page_is_idle(page)) {
 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(page);
 147                                 if (page_is_idle(page))
 148                                         *out |= 1ULL << bit;
 149                         }
 150                         put_page(page);
 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 page *page;
 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 = ALIGN(max_pfn, BITMAP_CHUNK_BITS);
 178
 179         for (; pfn < end_pfn; pfn++) {
 180                 bit = pfn % BITMAP_CHUNK_BITS;
 181                 if ((*in >> bit) & 1) {
 182                         page = page_idle_get_page(pfn);
 183                         if (page) {
 184                                 page_idle_clear_pte_refs(page);
 185                                 set_page_idle(page);
 186                                 put_page(page);
 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, S_IRUSR | S_IWUSR,
 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 struct attribute_group page_idle_attr_group = {
 206         .bin_attrs = page_idle_bin_attrs,
 207         .name = "page_idle",
 208 };
 209
 210 #ifndef CONFIG_64BIT
 211 static bool need_page_idle(void)
 212 {
 213         return true;
 214 }
 215 struct page_ext_operations page_idle_ops = {
 216         .need = need_page_idle,
 217 };
 218 #endif
 219
 220 static int __init page_idle_init(void)
 221 {
 222         int err;
 223
 224         err = sysfs_create_group(mm_kobj, &page_idle_attr_group);
 225         if (err) {
 226                 pr_err("page_idle: register sysfs failed\n");
 227                 return err;
 228         }
 229         return 0;
 230 }
 231 subsys_initcall(page_idle_init);