int madvise(void *start, size_t length, int advice);
The advice is indicated in the advice parameter which can be
| 標籤 | 描述 |
|---|---|
| MADV_NORMAL | |
| No special treatment. This is the default. | |
| MADV_RANDOM | |
| Expect page references in random order. (Hence, read ahead may be less useful than normally.) | |
| MADV_SEQUENTIAL | |
| Expect page references in sequential order. (Hence, pages in the given range can be aggressively read ahead, and may be freed soon after they are accessed.) | |
| MADV_WILLNEED | |
| Expect access in the near future. (Hence, it might be a good idea to read some pages ahead.) | |
| MADV_DONTNEED | |
| Do not expect access in the near future. (For the time being, the application is finished with the given range, so the kernel can free resources associated with it.) Subsequent accesses of pages in this range will succeed, but will result either in re-loading of the memory contents from the underlying mapped file (see mmap()) or zero-fill-on-demand pages for mappings without an underlying file. | |
| 標籤 | 描述 |
|---|---|
| EAGAIN | A kernel resource was temporarily unavailable. |
| EBADF | The map exists, but the area maps something that isn’t a file. |
| EINVAL | The value len is negative, start is not page-aligned, advice is not a valid value, or the application is attempting to release locked or shared pages (with MADV_DONTNEED). |
| EIO | (for MADV_WILLNEED) Paging in this area would exceed the process’s maximum resident set size. |
| ENOMEM | (for MADV_WILLNEED) Not enough memory: paging in failed. |
| ENOMEM | Addresses in the specified range are not currently mapped, or are outside the address space of the process. |
The current Linux implementation (2.4.0) views this system call more as a command than as advice and hence may return an error when it cannot do what it usually would do in response to this advice. (See the ERRORS description above.) This is nonstandard behaviour.
The Linux implementation requires that the address start be page-aligned, and allowslength to be zero. If there are some parts of the specified address range that are not mapped, the Linux version of madvise() ignores them and applies the call to the rest (but returns ENOMEM from the system call, as it should).