HUGECTL(8)HUGECTL(8)NAMEhugectl - Control policy for backing text, data and malloc() with
hugepages
SYNOPSIShugectl [options] command {arguments}
DESCRIPTIONhugectl 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 seg‐
ments. 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 environ‐
ment 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/Documentation/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 lib‐
hugetlbfs. 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 envi‐
ronment. 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 ALSOoprofile(1), hugeadm(7), libhugetlbfs(7)AUTHORS
libhugetlbfs was written by various people on the libhugetlbfs-devel
mailing list.
October 10, 2008 HUGECTL(8)
