LXR linux/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/mempolicy.h>
  12#include <linux/hugetlb.h>
  13#include <linux/sched.h>
  14
  15/*
  16 * Any behaviour which results in changes to the vma->vm_flags needs to
  17 * take mmap_sem for writing. Others, which simply traverse vmas, need
  18 * to only take it for reading.
  19 */
  20static int madvise_need_mmap_write(int behavior)
  21{
  22        switch (behavior) {
  23        case MADV_REMOVE:
  24        case MADV_WILLNEED:
  25        case MADV_DONTNEED:
  26                return 0;
  27        default:
  28                /* be safe, default to 1. list exceptions explicitly */
  29                return 1;
  30        }
  31}
  32
  33/*
  34 * We can potentially split a vm area into separate
  35 * areas, each area with its own behavior.
  36 */
  37static long madvise_behavior(struct vm_area_struct * vma,
  38                     struct vm_area_struct **prev,
  39                     unsigned long start, unsigned long end, int behavior)
  40{
  41        struct mm_struct * mm = vma->vm_mm;
  42        int error = 0;
  43        pgoff_t pgoff;
  44        int new_flags = vma->vm_flags;
  45
  46        switch (behavior) {
  47        case MADV_NORMAL:
  48                new_flags = new_flags & ~VM_RAND_READ & ~VM_SEQ_READ;
  49                break;
  50        case MADV_SEQUENTIAL:
  51                new_flags = (new_flags & ~VM_RAND_READ) | VM_SEQ_READ;
  52                break;
  53        case MADV_RANDOM:
  54                new_flags = (new_flags & ~VM_SEQ_READ) | VM_RAND_READ;
  55                break;
  56        case MADV_DONTFORK:
  57                new_flags |= VM_DONTCOPY;
  58                break;
  59        case MADV_DOFORK:
  60                new_flags &= ~VM_DONTCOPY;
  61                break;
  62        }
  63
  64        if (new_flags == vma->vm_flags) {
  65                *prev = vma;
  66                goto out;
  67        }
  68
  69        pgoff = vma->vm_pgoff + ((start - vma->vm_start) >> PAGE_SHIFT);
  70        *prev = vma_merge(mm, *prev, start, end, new_flags, vma->anon_vma,
  71                                vma->vm_file, pgoff, vma_policy(vma));
  72        if (*prev) {
  73                vma = *prev;
  74                goto success;
  75        }
  76
  77        *prev = vma;
  78
  79        if (start != vma->vm_start) {
  80                error = split_vma(mm, vma, start, 1);
  81                if (error)
  82                        goto out;
  83        }
  84
  85        if (end != vma->vm_end) {
  86                error = split_vma(mm, vma, end, 0);
  87                if (error)
  88                        goto out;
  89        }
  90
  91success:
  92        /*
  93         * vm_flags is protected by the mmap_sem held in write mode.
  94         */
  95        vma->vm_flags = new_flags;
  96
  97out:
  98        if (error == -ENOMEM)
  99                error = -EAGAIN;
 100        return error;
 101}
 102
 103/*
 104 * Schedule all required I/O operations.  Do not wait for completion.
 105 */
 106static long madvise_willneed(struct vm_area_struct * vma,
 107                             struct vm_area_struct ** prev,
 108                             unsigned long start, unsigned long end)
 109{
 110        struct file *file = vma->vm_file;
 111
 112        if (!file)
 113                return -EBADF;
 114
 115        /*
 116         * Page cache readahead assumes page cache pages are order-0 which
 117         * is not the case for hugetlbfs. Do not give a bad return value
 118         * but ignore the advice.
 119         */
 120        if (vma->vm_flags & VM_HUGETLB)
 121                return 0;
 122
 123        if (file->f_mapping->a_ops->get_xip_mem) {
 124                /* no bad return value, but ignore advice */
 125                return 0;
 126        }
 127
 128        *prev = vma;
 129        start = ((start - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
 130        if (end > vma->vm_end)
 131                end = vma->vm_end;
 132        end = ((end - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
 133
 134        force_page_cache_readahead(file->f_mapping,
 135                        file, start, max_sane_readahead(end - start));
 136        return 0;
 137}
 138
 139/*
 140 * Application no longer needs these pages.  If the pages are dirty,
 141 * it's OK to just throw them away.  The app will be more careful about
 142 * data it wants to keep.  Be sure to free swap resources too.  The
 143 * zap_page_range call sets things up for shrink_active_list to actually free
 144 * these pages later if no one else has touched them in the meantime,
 145 * although we could add these pages to a global reuse list for
 146 * shrink_active_list to pick up before reclaiming other pages.
 147 *
 148 * NB: This interface discards data rather than pushes it out to swap,
 149 * as some implementations do.  This has performance implications for
 150 * applications like large transactional databases which want to discard
 151 * pages in anonymous maps after committing to backing store the data
 152 * that was kept in them.  There is no reason to write this data out to
 153 * the swap area if the application is discarding it.
 154 *
 155 * An interface that causes the system to free clean pages and flush
 156 * dirty pages is already available as msync(MS_INVALIDATE).
 157 */
 158static long madvise_dontneed(struct vm_area_struct * vma,
 159                             struct vm_area_struct ** prev,
 160                             unsigned long start, unsigned long end)
 161{
 162        *prev = vma;
 163        if (vma->vm_flags & (VM_LOCKED|VM_HUGETLB|VM_PFNMAP))
 164                return -EINVAL;
 165
 166        if (unlikely(vma->vm_flags & VM_NONLINEAR)) {
 167                struct zap_details details = {
 168                        .nonlinear_vma = vma,
 169                        .last_index = ULONG_MAX,
 170                };
 171                zap_page_range(vma, start, end - start, &details);
 172        } else
 173                zap_page_range(vma, start, end - start, NULL);
 174        return 0;
 175}
 176
 177/*
 178 * Application wants to free up the pages and associated backing store.
 179 * This is effectively punching a hole into the middle of a file.
 180 *
 181 * NOTE: Currently, only shmfs/tmpfs is supported for this operation.
 182 * Other filesystems return -ENOSYS.
 183 */
 184static long madvise_remove(struct vm_area_struct *vma,
 185                                struct vm_area_struct **prev,
 186                                unsigned long start, unsigned long end)
 187{
 188        struct address_space *mapping;
 189        loff_t offset, endoff;
 190        int error;
 191
 192        *prev = NULL;   /* tell sys_madvise we drop mmap_sem */
 193
 194        if (vma->vm_flags & (VM_LOCKED|VM_NONLINEAR|VM_HUGETLB))
 195                return -EINVAL;
 196
 197        if (!vma->vm_file || !vma->vm_file->f_mapping
 198                || !vma->vm_file->f_mapping->host) {
 199                        return -EINVAL;
 200        }
 201
 202        if ((vma->vm_flags & (VM_SHARED|VM_WRITE)) != (VM_SHARED|VM_WRITE))
 203                return -EACCES;
 204
 205        mapping = vma->vm_file->f_mapping;
 206
 207        offset = (loff_t)(start - vma->vm_start)
 208                        + ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
 209        endoff = (loff_t)(end - vma->vm_start - 1)
 210                        + ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
 211
 212        /* vmtruncate_range needs to take i_mutex and i_alloc_sem */
 213        up_read(&current->mm->mmap_sem);
 214        error = vmtruncate_range(mapping->host, offset, endoff);
 215        down_read(&current->mm->mmap_sem);
 216        return error;
 217}
 218
 219static long
 220madvise_vma(struct vm_area_struct *vma, struct vm_area_struct **prev,
 221                unsigned long start, unsigned long end, int behavior)
 222{
 223        long error;
 224
 225        switch (behavior) {
 226        case MADV_DOFORK:
 227                if (vma->vm_flags & VM_IO) {
 228                        error = -EINVAL;
 229                        break;
 230                }
 231        case MADV_DONTFORK:
 232        case MADV_NORMAL:
 233        case MADV_SEQUENTIAL:
 234        case MADV_RANDOM:
 235                error = madvise_behavior(vma, prev, start, end, behavior);
 236                break;
 237        case MADV_REMOVE:
 238                error = madvise_remove(vma, prev, start, end);
 239                break;
 240
 241        case MADV_WILLNEED:
 242                error = madvise_willneed(vma, prev, start, end);
 243                break;
 244
 245        case MADV_DONTNEED:
 246                error = madvise_dontneed(vma, prev, start, end);
 247                break;
 248
 249        default:
 250                error = -EINVAL;
 251                break;
 252        }
 253        return error;
 254}
 255
 256/*
 257 * The madvise(2) system call.
 258 *
 259 * Applications can use madvise() to advise the kernel how it should
 260 * handle paging I/O in this VM area.  The idea is to help the kernel
 261 * use appropriate read-ahead and caching techniques.  The information
 262 * provided is advisory only, and can be safely disregarded by the
 263 * kernel without affecting the correct operation of the application.
 264 *
 265 * behavior values:
 266 *  MADV_NORMAL - the default behavior is to read clusters.  This
 267 *              results in some read-ahead and read-behind.
 268 *  MADV_RANDOM - the system should read the minimum amount of data
 269 *              on any access, since it is unlikely that the appli-
 270 *              cation will need more than what it asks for.
 271 *  MADV_SEQUENTIAL - pages in the given range will probably be accessed
 272 *              once, so they can be aggressively read ahead, and
 273 *              can be freed soon after they are accessed.
 274 *  MADV_WILLNEED - the application is notifying the system to read
 275 *              some pages ahead.
 276 *  MADV_DONTNEED - the application is finished with the given range,
 277 *              so the kernel can free resources associated with it.
 278 *  MADV_REMOVE - the application wants to free up the given range of
 279 *              pages and associated backing store.
 280 *
 281 * return values:
 282 *  zero    - success
 283 *  -EINVAL - start + len < 0, start is not page-aligned,
 284 *              "behavior" is not a valid value, or application
 285 *              is attempting to release locked or shared pages.
 286 *  -ENOMEM - addresses in the specified range are not currently
 287 *              mapped, or are outside the AS of the process.
 288 *  -EIO    - an I/O error occurred while paging in data.
 289 *  -EBADF  - map exists, but area maps something that isn't a file.
 290 *  -EAGAIN - a kernel resource was temporarily unavailable.
 291 */
 292SYSCALL_DEFINE3(madvise, unsigned long, start, size_t, len_in, int, behavior)
 293{
 294        unsigned long end, tmp;
 295        struct vm_area_struct * vma, *prev;
 296        int unmapped_error = 0;
 297        int error = -EINVAL;
 298        int write;
 299        size_t len;
 300
 301        write = madvise_need_mmap_write(behavior);
 302        if (write)
 303                down_write(&current->mm->mmap_sem);
 304        else
 305                down_read(&current->mm->mmap_sem);
 306
 307        if (start & ~PAGE_MASK)
 308                goto out;
 309        len = (len_in + ~PAGE_MASK) & PAGE_MASK;
 310
 311        /* Check to see whether len was rounded up from small -ve to zero */
 312        if (len_in && !len)
 313                goto out;
 314
 315        end = start + len;
 316        if (end < start)
 317                goto out;
 318
 319        error = 0;
 320        if (end == start)
 321                goto out;
 322
 323        /*
 324         * If the interval [start,end) covers some unmapped address
 325         * ranges, just ignore them, but return -ENOMEM at the end.
 326         * - different from the way of handling in mlock etc.
 327         */
 328        vma = find_vma_prev(current->mm, start, &prev);
 329        if (vma && start > vma->vm_start)
 330                prev = vma;
 331
 332        for (;;) {
 333                /* Still start < end. */
 334                error = -ENOMEM;
 335                if (!vma)
 336                        goto out;
 337
 338                /* Here start < (end|vma->vm_end). */
 339                if (start < vma->vm_start) {
 340                        unmapped_error = -ENOMEM;
 341                        start = vma->vm_start;
 342                        if (start >= end)
 343                                goto out;
 344                }
 345
 346                /* Here vma->vm_start <= start < (end|vma->vm_end) */
 347                tmp = vma->vm_end;
 348                if (end < tmp)
 349                        tmp = end;
 350
 351                /* Here vma->vm_start <= start < tmp <= (end|vma->vm_end). */
 352                error = madvise_vma(vma, &prev, start, tmp, behavior);
 353                if (error)
 354                        goto out;
 355                start = tmp;
 356                if (prev && start < prev->vm_end)
 357                        start = prev->vm_end;
 358                error = unmapped_error;
 359                if (start >= end)
 360                        goto out;
 361                if (prev)
 362                        vma = prev->vm_next;
 363                else    /* madvise_remove dropped mmap_sem */
 364                        vma = find_vma(current->mm, start);
 365        }
 366out:
 367        if (write)
 368                up_write(&current->mm->mmap_sem);
 369        else
 370                up_read(&current->mm->mmap_sem);
 371
 372        return error;
 373}
 374