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,
  65                                              PAGE_CHECK_ADDRESS_PMD_FLAG, &ptl);
  66                 if (pmd) {
  67                         referenced = pmdp_clear_young_notify(vma, addr, pmd);
  68                         spin_unlock(ptl);
  69                 }
  70         } else {
  71                 pte = page_check_address(page, mm, addr, &ptl, 0);
  72                 if (pte) {
  73                         referenced = ptep_clear_young_notify(vma, addr, pte);
  74                         pte_unmap_unlock(pte, ptl);
  75                 }
  76         }
  77         if (referenced) {
  78                 clear_page_idle(page);
  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                  * page_referenced() will return > 0.
  83                  */
  84                 set_page_young(page);
  85         }
  86         return SWAP_AGAIN;
  87 }
  88
  89 static void page_idle_clear_pte_refs(struct page *page)
  90 {
  91         /*
  92          * Since rwc.arg is unused, rwc is effectively immutable, so we
  93          * can make it static const to save some cycles and stack.
  94          */
  95         static const struct rmap_walk_control rwc = {
  96                 .rmap_one = page_idle_clear_pte_refs_one,
  97                 .anon_lock = page_lock_anon_vma_read,
  98         };
  99         bool need_lock;
 100
 101         if (!page_mapped(page) ||
 102             !page_rmapping(page))
 103                 return;
 104
 105         need_lock = !PageAnon(page) || PageKsm(page);
 106         if (need_lock && !trylock_page(page))
 107                 return;
 108
 109         rmap_walk(page, (struct rmap_walk_control *)&rwc);
 110
 111         if (need_lock)
 112                 unlock_page(page);
 113 }
 114
 115 static ssize_t page_idle_bitmap_read(struct file *file, struct kobject *kobj,
 116                                      struct bin_attribute *attr, char *buf,
 117                                      loff_t pos, size_t count)
 118 {
 119         u64 *out = (u64 *)buf;
 120         struct page *page;
 121         unsigned long pfn, end_pfn;
 122         int bit;
 123
 124         if (pos % BITMAP_CHUNK_SIZE || count % BITMAP_CHUNK_SIZE)
 125                 return -EINVAL;
 126
 127         pfn = pos * BITS_PER_BYTE;
 128         if (pfn >= max_pfn)
 129                 return 0;
 130
 131         end_pfn = pfn + count * BITS_PER_BYTE;
 132         if (end_pfn > max_pfn)
 133                 end_pfn = ALIGN(max_pfn, BITMAP_CHUNK_BITS);
 134
 135         for (; pfn < end_pfn; pfn++) {
 136                 bit = pfn % BITMAP_CHUNK_BITS;
 137                 if (!bit)
 138                         *out = 0ULL;
 139                 page = page_idle_get_page(pfn);
 140                 if (page) {
 141                         if (page_is_idle(page)) {
 142                                 /*
 143                                  * The page might have been referenced via a
 144                                  * pte, in which case it is not idle. Clear
 145                                  * refs and recheck.
 146                                  */
 147                                 page_idle_clear_pte_refs(page);
 148                                 if (page_is_idle(page))
 149                                         *out |= 1ULL << bit;
 150                         }
 151                         put_page(page);
 152                 }
 153                 if (bit == BITMAP_CHUNK_BITS - 1)
 154                         out++;
 155                 cond_resched();
 156         }
 157         return (char *)out - buf;
 158 }
 159
 160 static ssize_t page_idle_bitmap_write(struct file *file, struct kobject *kobj,
 161                                       struct bin_attribute *attr, char *buf,
 162                                       loff_t pos, size_t count)
 163 {
 164         const u64 *in = (u64 *)buf;
 165         struct page *page;
 166         unsigned long pfn, end_pfn;
 167         int bit;
 168
 169         if (pos % BITMAP_CHUNK_SIZE || count % BITMAP_CHUNK_SIZE)
 170                 return -EINVAL;
 171
 172         pfn = pos * BITS_PER_BYTE;
 173         if (pfn >= max_pfn)
 174                 return -ENXIO;
 175
 176         end_pfn = pfn + count * BITS_PER_BYTE;
 177         if (end_pfn > max_pfn)
 178                 end_pfn = ALIGN(max_pfn, BITMAP_CHUNK_BITS);
 179
 180         for (; pfn < end_pfn; pfn++) {
 181                 bit = pfn % BITMAP_CHUNK_BITS;
 182                 if ((*in >> bit) & 1) {
 183                         page = page_idle_get_page(pfn);
 184                         if (page) {
 185                                 page_idle_clear_pte_refs(page);
 186                                 set_page_idle(page);
 187                                 put_page(page);
 188                         }
 189                 }
 190                 if (bit == BITMAP_CHUNK_BITS - 1)
 191                         in++;
 192                 cond_resched();
 193         }
 194         return (char *)in - buf;
 195 }
 196
 197 static struct bin_attribute page_idle_bitmap_attr =
 198                 __BIN_ATTR(bitmap, S_IRUSR | S_IWUSR,
 199                            page_idle_bitmap_read, page_idle_bitmap_write, 0);
 200
 201 static struct bin_attribute *page_idle_bin_attrs[] = {
 202         &page_idle_bitmap_attr,
 203         NULL,
 204 };
 205
 206 static struct attribute_group page_idle_attr_group = {
 207         .bin_attrs = page_idle_bin_attrs,
 208         .name = "page_idle",
 209 };
 210
 211 #ifndef CONFIG_64BIT
 212 static bool need_page_idle(void)
 213 {
 214         return true;
 215 }
 216 struct page_ext_operations page_idle_ops = {
 217         .need = need_page_idle,
 218 };
 219 #endif
 220
 221 static int __init page_idle_init(void)
 222 {
 223         int err;
 224
 225         err = sysfs_create_group(mm_kobj, &page_idle_attr_group);
 226         if (err) {
 227                 pr_err("page_idle: register sysfs failed\n");
 228                 return err;
 229         }
 230         return 0;
 231 }
 232 subsys_initcall(page_idle_init);