1ALLOC_HUGEPAGES(2) Linux Programmer's Manual ALLOC_HUGEPAGES(2)
2
6 alloc_hugepages, free_hugepages - allocate or free huge pages
7
9 void *alloc_hugepages(int key, void *addr, size_t len,
10 int prot, int flag);
11 int free_hugepages(void *addr);
13
15 The system calls alloc_hugepages() and free_hugepages() were introduced
16 in Linux 2.5.36 and removed again in 2.5.54. They existed only on i386
17 and ia64 (when built with CONFIG_HUGETLB_PAGE). In Linux 2.4.20 the
18 syscall numbers exist, but the calls fail with the error ENOSYS.
19 On i386 the memory management hardware knows about ordinary pages (4
21 KiB) and huge pages (2 or 4 MiB). Similarly ia64 knows about huge
22 pages of several sizes. These system calls serve to map huge pages
23 into the process's memory or to free them again. Huge pages are locked
24 into memory, and are not swapped.
25 The key argument is an identifier. When zero the pages are private,
27 and not inherited by children. When positive the pages are shared with
28 other applications using the same key, and inherited by child pro‐
29 cesses.
30 The addr argument of free_hugepages() tells which page is being freed:
32 it was the return value of a call to alloc_hugepages(). (The memory is
33 first actually freed when all users have released it.) The addr argu‐
34 ment of alloc_hugepages() is a hint, that the kernel may or may not
35 follow. Addresses must be properly aligned.
36 The len argument is the length of the required segment. It must be a
38 multiple of the huge page size.
39 The prot argument specifies the memory protection of the segment. It
41 is one of PROT_READ, PROT_WRITE, PROT_EXEC.
42 The flag argument is ignored, unless key is positive. In that case, if
44 flag is IPC_CREAT, then a new huge page segment is created when none
45 with the given key existed. If this flag is not set, then ENOENT is
46 returned when no segment with the given key exists.
47
49 On success, alloc_hugepages() returns the allocated virtual address,
50 and free_hugepages() returns zero. On error, -1 is returned, and errno
51 is set appropriately.
52
54 ENOSYS The system call is not supported on this kernel.
55
57 /proc/sys/vm/nr_hugepages Number of configured hugetlb pages. This can
58 be read and written.
59 /proc/meminfo Gives info on the number of configured hugetlb pages and
61 on their size in the three variables HugePages_Total, HugePages_Free,
62 Hugepagesize.
63
65 These calls are specific to Linux on Intel processors, and should not
66 be used in programs intended to be portable.
67
69 These system calls are gone; they existed only in Linux 2.5.36 through
70 to 2.5.54. Now the hugetlbfs file system can be used instead. Memory
71 backed by huge pages (if the CPU supports them) is obtained by using
72 mmap(2) to map files in this virtual file system.
73 The maximal number of huge pages can be specified using the hugepages=
75 boot parameter.
76
79 This page is part of release 3.25 of the Linux man-pages project. A
80 description of the project, and information about reporting bugs, can
81 be found at http://www.kernel.org/doc/man-pages/.
82Linux 2007-05-31 ALLOC_HUGEPAGES(2)