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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.

--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.

SEE ALSO

oprofile(1), hugeadm(7), libhugetlbfs(7)

AUTHORS

libhugetlbfs was written by various people on the libhugetlbfs-devel mailing list.