Manpage of REMAP_FILE_PAGES
REMAP_FILE_PAGESSection: Linux Programmer's Manual (2)
NAMEremap_file_pages - create a nonlinear file mapping
#define _GNU_SOURCE /* See feature_test_macros(7) */ #include <sys/mman.h>int remap_file_pages(void *addr, size_t size, int prot, size_t pgoff, int flags);
DESCRIPTIONNote: this system call was marked as deprecated starting with Linux 3.16. In Linux 4.0, the implementation was replaced by a slower in-kernel emulation. Those few applications that use this system call should consider migrating to alternatives. This change was made because the kernel code for this system call was complex, and it is believed to be little used or perhaps even completely unused. While it had some use cases in database applications on 32-bit systems, those use cases don't exist on 64-bit systems.
The remap_file_pages() system call is used to create a nonlinear mapping, that is, a mapping in which the pages of the file are mapped into a nonsequential order in memory. The advantage of using remap_file_pages() over using repeated calls to mmap(2) is that the former approach does not require the kernel to create additional VMA (Virtual Memory Area) data structures.
To create a nonlinear mapping we perform the following steps:
- Use mmap(2) to create a mapping (which is initially linear). This mapping must be created with the MAP_SHAREDflag.
- Use one or more calls to remap_file_pages() to rearrange the correspondence between the pages of the mapping and the pages of the file. It is possible to map the same page of a file into multiple locations within the mapped region.
The pgoffand sizearguments specify the region of the file that is to be relocated within the mapping: pgoffis a file offset in units of the system page size; sizeis the length of the region in bytes.
The addrargument serves two purposes. First, it identifies the mapping whose pages we want to rearrange. Thus, addrmust be an address that falls within a region mmap(2). Second, addrspecifies the address at which the file pages identified by pgoffand sizewill be placed.ly mapped by a call to
The values specified in addrand sizeshould be multiples of the system page size. If they are not, then the kernel rounds bothvalues downto the nearest multiple of the page size.
The protargument must be specified as 0.
The flagsargument has the same meaning as for mmap(2), but all flags other than MAP_NONBLOCKare ignored.
RETURN VALUEOn success, remap_file_pages() returns 0. On error, -1 is returned, and errnois set appropriately.
- addrdoes not refer to a valid mapping created with the MAP_SHAREDflag.
- addr, size, prot, or pgoffis invalid.
VERSIONSThe remap_file_pages() system call appeared in Linux 2.5.46; glibc support was added in version 2.3.3.
CONFORMING TOThe remap_file_pages() system call is Linux-specific.
NOTESSince Linux 2.6.23, remap_file_pages() creates non-linear mappings only on in-memory filesystems such as tmpfs(5), hugetlbfs or ramfs. On filesystems with a backing store, remap_file_pages() is not much more efficient than using mmap(2) to adjust which parts of the file are mapped to which addresses.
SEE ALSOgetpagesize(2), mmap(2), mmap2(2), mprotect(2), mremap(2), msync(2)
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