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free_hugepage_region(3) [centos man page]

GET_HUGEPAGE_REGION(3)					     Library Functions Manual					    GET_HUGEPAGE_REGION(3)

NAME
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)

Check Out this Related Man Page

HUGECTL(8)						      System Manager's Manual							HUGECTL(8)

NAME
hugectl - Control policy for backing text, data and malloc() with hugepages SYNOPSIS
hugectl [options] command {arguments} DESCRIPTION
hugectl runs processes with a specific policy for backing memory regions with hugepages. The use of hugepages benefit applications that use large amounts of address space and suffer a performance hit due to TLB misses. Policy is enforced by libhugetlbfs and hugectl configures the environment based on the options provided. Wall-clock time or oprofile can be used to determine if there is a performance benefit from using hugepages or not. To effectively back text/data, the target process must be relinked to align the ELF segments on a hugepage boundary. The library also sup- ports more options for the control of memory regions than are exposed by the hugectl utility. See the libhugetlbfs manual page for more details. The following options affect what memory regions are backed by hugepages. --text[=<size>],--data[=<size>],--bss[=<size>] Back the text, data or BSS segments with hugepages, optionally with pages of the specified size. To be effective, the process must be relinked as described in the HOWTO to align the ELF segments. It is possible to partially back segments using the HUGETLB_FORCE_ELMAP environment variable as described in the libhugetlbfs manual page. --heap[=<size>] Use the glibc morecore hook to back malloc() with hugepages, optionally with pages of the specified size. Note that this does not affect brk() segments and applications that use custom allocators potentially do not use hugepages for their heap even with this option specified. --shm This option overrides shmget() to back shared memory regions with hugepages if possible. Segment size requests will be aligned to fit to the default hugepage size region. --share-text Request that multiple application instances share text segments that are backed with huge pages. This option sets the environment variable HUGETLB_SHARE to 1. --thp Align heap regions to huge page size for promotion by khugepaged. For more information on transparent huge pages see linux-2.6/Doc- umentation/transhuge.txt The following options affect how hugectl behaves. --no-preload Disable any pre-loading of the libhugetlbfs library. This may be necessary if only the heap is being backed by hugepages and the application is already linked against the library. hugectl may pre-load the library by mistake and this option prevents that. --force-preload Force pre-loading of the libhugetlbfs library. This option is used when the segments of the binary are aligned to the hugepage boundary of interest but the binary is not linked against libhugetlbfs. This is useful on PPC64 where binaries are aligned to 64K as required by the ABI and the kernel is using a 4K base pagesize. --no-reserve By default, huge pages are reserved at mmap() time so future faults will succeed. This avoids unexpected application but some appli- cations depend on memory overcommit to create large sparse mappings. For this type of application, this switch will create huge page backed mappings without a reservation if the kernel is recent enough to make this operation safe. Use this option with extreme care as in the event huge pages are not available when the mapping is faulted, the application will be killed. --dry-run Instead of running the process, the hugectl utility will describe what environment variables it set for libhugetlbfs. This is useful if additional environment variables are to be set and a launcher shell script is being developed. --library-use-path By default, hugectl will use the version of libhugetlbfs it was installed with, even if this is not in the LD_LIBRARY_PATH environ- ment. Using this option forces hugectl to use the version of libhugetlbfs installed in the library system path. --library-path <path> This option forces hugectl to use the libhugetlbfs libraries within the given prefix. The following options affect the verbosity of libhugetlbfs. --verbose <level>, -v The default value for the verbosity level is 1 and the range of the value can be set with --verbose from 0 to 99. The higher the value, the more verbose the library will be. 0 is quiet and 3 will output much debugging information. The verbosity level is increased by one each time -v is specified. -q The -q option will drecease the verbosity level by 1 each time it is specified to a minimum of 0. SEE ALSO
oprofile(1), hugeadm(7), libhugetlbfs(7) AUTHORS
libhugetlbfs was written by various people on the libhugetlbfs-devel mailing list. October 10, 2008 HUGECTL(8)
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