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get_hugepage_region(3) [centos man page]

GET_HUGEPAGE_REGION(3)					     Library Functions Manual					    GET_HUGEPAGE_REGION(3)

get_hugepage_region, free_hugepage_region - Allocate and free regions of memory that use hugepages where possible SYNOPSIS
#include <hugetlbfs.h> void *get_hugepage_region(size_t len, ghr_t flags); void free_hugepage_region(void *ptr); DESCRIPTION
get_hugepage_region() allocates a memory region len bytes in size backed by hugepages. Hugepages may be of benefit to applications that use large amounts of address space and suffer a performance hit due to TLB misses. Wall-clock time or oprofile can be used to determine if there is a performance benefit from using hugepages or not. Unlike get_huge_pages(), len does not have to be hugepage-aligned although memory may be wasted due to alignment. The caller may also spec- ify that base pages be used in the event there are no hugepages available. The flags argument changes the behaviour of the function. Flags may be or'd together. GHR_FALLBACK Use base pages if there are an insufficient number of huge pages. GHR_STRICT Use hugepages or return NULL. GHR_COLOR When specified, bytes that would be wasted due to alignment are used to color the buffer by offsetting it by a random cacheline within the hugepage. This avoids a performance problem whereby multiple buffers use the same cache lines at the same offsets. If it is not important that the start of the buffer be page-aligned, specify this flag. GHR_DEFAULT The library chooses a sensible combination of flags for allocating a region of memory. The current default is: GHR_FALLBACK | GHR_COLOR free_hugepage_region() frees a region of memory allocated by get_hugepage_region(). The behaviour of the function if another pointer is used, valid or otherwise, is undefined. RETURN VALUE
On success, a pointer is returned for to the allocated memory. On error, NULL is returned. errno will be set based on what the failure of mmap() was due to. SEE ALSO
oprofile(1) , gethugepagesize(3) , get_huge_pages(3) , libhugetlbfs(7) AUTHORS
libhugetlbfs was written by various people on the libhugetlbfs-devel mailing list. November 7, 2008 GET_HUGEPAGE_REGION(3)

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ALLOC_HUGEPAGES(2)					     Linux Programmer's Manual						ALLOC_HUGEPAGES(2)

alloc_hugepages, free_hugepages - allocate or free huge pages SYNOPSIS
void *alloc_hugepages(int key, void *addr, size_t len, int prot, int flag); int free_hugepages(void *addr); DESCRIPTION
The system calls alloc_hugepages() and free_hugepages() were introduced in Linux 2.5.36 and removed again in 2.5.54. They existed only on i386 and ia64 (when built with CONFIG_HUGETLB_PAGE). In Linux 2.4.20 the syscall numbers exist, but the calls fail with the error ENOSYS. On i386 the memory management hardware knows about ordinary pages (4 KiB) and huge pages (2 or 4 MiB). Similarly ia64 knows about huge pages of several sizes. These system calls serve to map huge pages into the process's memory or to free them again. Huge pages are locked into memory, and are not swapped. The key argument is an identifier. When zero the pages are private, and not inherited by children. When positive the pages are shared with other applications using the same key, and inherited by child processes. The addr argument of free_hugepages() tells which page is being freed: it was the return value of a call to alloc_hugepages(). (The memory is first actually freed when all users have released it.) The addr argument of alloc_hugepages() is a hint, that the kernel may or may not follow. Addresses must be properly aligned. The len argument is the length of the required segment. It must be a multiple of the huge page size. The prot argument specifies the memory protection of the segment. It is one of PROT_READ, PROT_WRITE, PROT_EXEC. The flag argument is ignored, unless key is positive. In that case, if flag is IPC_CREAT, then a new huge page segment is created when none with the given key existed. If this flag is not set, then ENOENT is returned when no segment with the given key exists. RETURN VALUE
On success, alloc_hugepages() returns the allocated virtual address, and free_hugepages() returns zero. On error, -1 is returned, and errno is set appropriately. ERRORS
ENOSYS The system call is not supported on this kernel. FILES
/proc/sys/vm/nr_hugepages Number of configured hugetlb pages. This can be read and written. /proc/meminfo Gives info on the number of configured hugetlb pages and on their size in the three variables HugePages_Total, HugePages_Free, Hugepagesize. CONFORMING TO
These calls are specific to Linux on Intel processors, and should not be used in programs intended to be portable. NOTES
These system calls are gone; they existed only in Linux 2.5.36 through to 2.5.54. Now the hugetlbfs file system can be used instead. Mem- ory backed by huge pages (if the CPU supports them) is obtained by using mmap(2) to map files in this virtual file system. The maximal number of huge pages can be specified using the hugepages= boot parameter. COLOPHON
This page is part of release 3.27 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at Linux 2007-05-31 ALLOC_HUGEPAGES(2)
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