mm/madvise.c

   1 /*
   2  *      linux/mm/madvise.c
   3  *
   4  * Copyright (C) 1999  Linus Torvalds
   5  * Copyright (C) 2002  Christoph Hellwig
   6  */
   7
   8 #include <linux/mman.h>
   9 #include <linux/pagemap.h>
  10 #include <linux/syscalls.h>
  11 #include <linux/hugetlb.h>
  12
  13 /*
  14  * We can potentially split a vm area into separate
  15  * areas, each area with its own behavior.
  16  */
  17 static long madvise_behavior(struct vm_area_struct * vma, unsigned long start,
  18                              unsigned long end, int behavior)
  19 {
  20         struct mm_struct * mm = vma->vm_mm;
  21         int error = 0;
  22
  23         if (start != vma->vm_start) {
  24                 error = split_vma(mm, vma, start, 1);
  25                 if (error)
  26                         goto out;
  27         }
  28
  29         if (end != vma->vm_end) {
  30                 error = split_vma(mm, vma, end, 0);
  31                 if (error)
  32                         goto out;
  33         }
  34
  35         /*
  36          * vm_flags is protected by the mmap_sem held in write mode.
  37          */
  38         VM_ClearReadHint(vma);
  39
  40         switch (behavior) {
  41         case MADV_SEQUENTIAL:
  42                 vma->vm_flags |= VM_SEQ_READ;
  43                 break;
  44         case MADV_RANDOM:
  45                 vma->vm_flags |= VM_RAND_READ;
  46                 break;
  47         default:
  48                 break;
  49         }
  50
  51 out:
  52         if (error == -ENOMEM)
  53                 error = -EAGAIN;
  54         return error;
  55 }
  56
  57 /*
  58  * Schedule all required I/O operations.  Do not wait for completion.
  59  */
  60 static long madvise_willneed(struct vm_area_struct * vma,
  61                              unsigned long start, unsigned long end)
  62 {
  63         struct file *file = vma->vm_file;
  64
  65         if (!file)
  66                 return -EBADF;
  67
  68         start = ((start - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
  69         if (end > vma->vm_end)
  70                 end = vma->vm_end;
  71         end = ((end - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
  72
  73         force_page_cache_readahead(file->f_mapping,
  74                         file, start, max_sane_readahead(end - start));
  75         return 0;
  76 }
  77
  78 /*
  79  * Application no longer needs these pages.  If the pages are dirty,
  80  * it's OK to just throw them away.  The app will be more careful about
  81  * data it wants to keep.  Be sure to free swap resources too.  The
  82  * zap_page_range call sets things up for refill_inactive to actually free
  83  * these pages later if no one else has touched them in the meantime,
  84  * although we could add these pages to a global reuse list for
  85  * refill_inactive to pick up before reclaiming other pages.
  86  *
  87  * NB: This interface discards data rather than pushes it out to swap,
  88  * as some implementations do.  This has performance implications for
  89  * applications like large transactional databases which want to discard
  90  * pages in anonymous maps after committing to backing store the data
  91  * that was kept in them.  There is no reason to write this data out to
  92  * the swap area if the application is discarding it.
  93  *
  94  * An interface that causes the system to free clean pages and flush
  95  * dirty pages is already available as msync(MS_INVALIDATE).
  96  */
  97 static long madvise_dontneed(struct vm_area_struct * vma,
  98                              unsigned long start, unsigned long end)
  99 {
 100         if ((vma->vm_flags & VM_LOCKED) || is_vm_hugetlb_page(vma))
 101                 return -EINVAL;
 102
 103         if (unlikely(vma->vm_flags & VM_NONLINEAR)) {
 104                 struct zap_details details = {
 105                         .nonlinear_vma = vma,
 106                         .last_index = ULONG_MAX,
 107                 };
 108                 zap_page_range(vma, start, end - start, &details);
 109         } else
 110                 zap_page_range(vma, start, end - start, NULL);
 111         return 0;
 112 }
 113
 114 static long madvise_vma(struct vm_area_struct * vma, unsigned long start,
 115                         unsigned long end, int behavior)
 116 {
 117         long error = -EBADF;
 118
 119         switch (behavior) {
 120         case MADV_NORMAL:
 121         case MADV_SEQUENTIAL:
 122         case MADV_RANDOM:
 123                 error = madvise_behavior(vma, start, end, behavior);
 124                 break;
 125
 126         case MADV_WILLNEED:
 127                 error = madvise_willneed(vma, start, end);
 128                 break;
 129
 130         case MADV_DONTNEED:
 131                 error = madvise_dontneed(vma, start, end);
 132                 break;
 133
 134         default:
 135                 error = -EINVAL;
 136                 break;
 137         }
 138
 139         return error;
 140 }
 141
 142 /*
 143  * The madvise(2) system call.
 144  *
 145  * Applications can use madvise() to advise the kernel how it should
 146  * handle paging I/O in this VM area.  The idea is to help the kernel
 147  * use appropriate read-ahead and caching techniques.  The information
 148  * provided is advisory only, and can be safely disregarded by the
 149  * kernel without affecting the correct operation of the application.
 150  *
 151  * behavior values:
 152  *  MADV_NORMAL - the default behavior is to read clusters.  This
 153  *              results in some read-ahead and read-behind.
 154  *  MADV_RANDOM - the system should read the minimum amount of data
 155  *              on any access, since it is unlikely that the appli-
 156  *              cation will need more than what it asks for.
 157  *  MADV_SEQUENTIAL - pages in the given range will probably be accessed
 158  *              once, so they can be aggressively read ahead, and
 159  *              can be freed soon after they are accessed.
 160  *  MADV_WILLNEED - the application is notifying the system to read
 161  *              some pages ahead.
 162  *  MADV_DONTNEED - the application is finished with the given range,
 163  *              so the kernel can free resources associated with it.
 164  *
 165  * return values:
 166  *  zero    - success
 167  *  -EINVAL - start + len < 0, start is not page-aligned,
 168  *              "behavior" is not a valid value, or application
 169  *              is attempting to release locked or shared pages.
 170  *  -ENOMEM - addresses in the specified range are not currently
 171  *              mapped, or are outside the AS of the process.
 172  *  -EIO    - an I/O error occurred while paging in data.
 173  *  -EBADF  - map exists, but area maps something that isn't a file.
 174  *  -EAGAIN - a kernel resource was temporarily unavailable.
 175  */
 176 asmlinkage long sys_madvise(unsigned long start, size_t len_in, int behavior)
 177 {
 178         unsigned long end;
 179         struct vm_area_struct * vma;
 180         int unmapped_error = 0;
 181         int error = -EINVAL;
 182         size_t len;
 183
 184         down_write(&current->mm->mmap_sem);
 185
 186         if (start & ~PAGE_MASK)
 187                 goto out;
 188         len = (len_in + ~PAGE_MASK) & PAGE_MASK;
 189
 190         /* Check to see whether len was rounded up from small -ve to zero */
 191         if (len_in && !len)
 192                 goto out;
 193
 194         end = start + len;
 195         if (end < start)
 196                 goto out;
 197
 198         error = 0;
 199         if (end == start)
 200                 goto out;
 201
 202         /*
 203          * If the interval [start,end) covers some unmapped address
 204          * ranges, just ignore them, but return -ENOMEM at the end.
 205          */
 206         vma = find_vma(current->mm, start);
 207         for (;;) {
 208                 /* Still start < end. */
 209                 error = -ENOMEM;
 210                 if (!vma)
 211                         goto out;
 212
 213                 /* Here start < vma->vm_end. */
 214                 if (start < vma->vm_start) {
 215                         unmapped_error = -ENOMEM;
 216                         start = vma->vm_start;
 217                 }
 218
 219                 /* Here vma->vm_start <= start < vma->vm_end. */
 220                 if (end <= vma->vm_end) {
 221                         if (start < end) {
 222                                 error = madvise_vma(vma, start, end,
 223                                                         behavior);
 224                                 if (error)
 225                                         goto out;
 226                         }
 227                         error = unmapped_error;
 228                         goto out;
 229                 }
 230
 231                 /* Here vma->vm_start <= start < vma->vm_end < end. */
 232                 error = madvise_vma(vma, start, vma->vm_end, behavior);
 233                 if (error)
 234                         goto out;
 235                 start = vma->vm_end;
 236                 vma = vma->vm_next;
 237         }
 238
 239 out:
 240         up_write(&current->mm->mmap_sem);
 241         return error;
 242 }