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hugectl

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 supports 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.

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 applications 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 environment. 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.