hugeadm man page
hugeadm — Configure the system huge page pools
hugeadm displays and configures the systems huge page pools. The size of the pools is set as a minimum and maximum threshold. The minimum value is allocated up front by the kernel and guaranteed to remain as hugepages until the pool is shrunk. If a maximum is set, the system will dynamically allocate pages if applications request more hugepages than the minimum size of the pool. There is no guarantee that more pages than this minimum pool size can be allocated.
The following options create mounts hugetlbfs mount points.
- This creates mount points for each supported huge page size under /var/lib/hugetlbfs. After creation they are mounts and are owned by root:root with permissions set to 770. Each mount point is named pagesize-<size in bytes>.
- This creates mount points for each supported huge page size under /var/lib/hugetlbfs/user/<user>. Mount point naming is the same as --create-mounts. After creation they are mounted and are owned by <user>:root with permissions set to 700.
- This creates mount points for each supported huge page size under /var/lib/hugetlbfs/group/<group>. Mount point naming is the same as --create-mounts. After creation they are mounted and are owned by root:<group> with permissions set to 070.
This creates mount points for each supported huge page size under /var/lib/hugetlbfs/global. Mount point naming is the same as --create-mounts. After creation they are mounted and are owned by root:root with permissions set to 1777.
The following options affect how mount points are created.
- This option is used in conjunction with --create-*-mounts. It limits the maximum amount of memory used by files within the mount point rounded up to the nearest huge page size. This can be used for example to grant different huge page quotas to individual users or groups.
This option is used in conjunction with --create-*-mounts. It limits the number of inodes (e.g. files) that can be created on the new mount points. This limits the number of mappings that can be created on a mount point. It could be used for example to limit the number of application instances that used a mount point as long as it was known how many inodes each application instance required.
The following options display information about the pools.
- This displays the Minimum, Current and Maximum number of huge pages in the pool for each pagesize supported by the system. The "Minimum" value is the size of the static pool and there will always be at least this number of hugepages in use by the system, either by applications or kept by the kernel in a reserved pool. The "Current" value is the number of hugepages currently in use, either by applications or stored on the kernels free list. The "Maximum" value is the largest number of hugepages that can be in use at any given time.
- Fragmentation avoidance in the kernel depends on avoiding pages of different mobility types being mixed with a pageblock arena - typically the size of the default huge page size. The more mixing that occurs, the less likely the huge page pool will be able to dynamically resize. The easiest means of avoiding mixing is to increase /proc/sys/vm/min_free_kbytes. This parameter sets min_free_kbytes to a recommended value to aid fragmentation avoidance.
- The maximum shared memory segment size should be set to at least the size of the largest shared memory segment size you want available for applications using huge pages, via /proc/sys/kernel/shmmax. Optionally, it can be set automatically to match the maximum possible size of all huge page allocations and thus the maximum possible shared memory segment size, using this switch.
- Users in the group specified in /proc/sys/vm/hugetlb_shm_group are granted full access to huge pages. The sysctl takes a numeric gid, but this hugeadm option can set it for you, using either a gid or group name.
- This displays every page size supported by the system and has a pool configured.
- This displays all page sizes supported by the system, even if no pool is available.
- This displays all active mount points for hugetlbfs.
The following options configure the pool.
- This option sets or adjusts the Minimum number of hugepages in the pool for pagesize size. size may be specified in bytes or in kilobytes, megabytes, or gigabytes by appending K, M, or G respectively, or as DEFAULT, which uses the system's default huge page size for size. The pool size adjustment can be specified by pagecount pages or by memsize, if postfixed with G, M, or K, for gigabytes, megabytes, or kilobytes, respectively. If the adjustment is specified via memsize, then the pagecount will be calculated for you, based on page size size. The pool is set to pagecount pages if + or - are not specified. If + or - are specified, then the size of the pool will adjust by that amount. Note that there is no guarantee that the system can allocate the hugepages requested for the Minimum pool. The size of the pools should be checked after executing this command to ensure they were successful.
- This option requests that allocation of huge pages to the static pool with --pool-pages-min obey the NUMA memory policy of the current process. This policy can be explicitly specified using numactl or inherited from a parent process.
- This option sets or adjusts the Maximum number of hugepages. Note that while the Minimum number of pages are guaranteed to be available to applications, there is not guarantee that the system can allocate the pages on demand when the number of huge pages requested by applications is between the Minimum and Maximum pool sizes. See --pool-pages-min for usage syntax.
- This option enables the use of the MOVABLE zone for the allocation of hugepages. This zone is created when kernelcore= or movablecore= are specified on the kernel command line but the zone is not used for the allocation of huge pages by default as the intended use for the zone may be to guarantee that memory can be off-lined and hot-removed. The kernel guarantees that the pages within this zone can be reclaimed unlike some kernel buffers for example. Unless pages are locked with mlock(), the hugepage pool can grow to at least the size of the movable zone once this option is set. Use sysctl to permanently enable the use of the MOVABLE zone for the allocation of huge pages.
- This option disables the use of the MOVABLE zone for the future allocation of huge pages. Note that existing huge pages are not reclaimed from the zone. Use sysctl to permanently disable the use of the MOVABLE zone for the allocation of huge pages.
- This option is specified with --pool-pages-min to retry allocations multiple times on failure to allocate the desired count of pages. It initially tries to resize the pool up to 5 times and continues to try if progress is being made towards the resize.
- This options is specified with --pool-pages-min to initialize a temporary swap file for the duration of the pool resize. When increasing the size of the pool, it can be necessary to reclaim pages so that contiguous memory is freed and this often requires swap to be successful. Swap is only created for a positive resize, and is then removed once the resize operation is completed. The default swap size is 5 huge pages, the optional argument <count> sets the swap size to <count> huge pages.
- This option is specified with --pool-pages-min to initialize swap in memory on ram disks. When increasing the size of the pool, it can be necessary to reclaim pages so that contiguous memory is freed and this often requires swap to be successful. If there isn't enough free disk space, swap can be initialized in RAM using this option. If the size of one ramdisk is not greater than the huge page size, then swap is initialized on multiple ramdisks. Swap is only created for a positive resize, and by default is removed once the resize operation is completed.
- This option is specified with the --add-temp-swap or --add-ramdisk-swap to make the swap space persist after the resize operation is completed. The swap spaces can later be removed manually using the swapoff command.
The following options tune the transparent huge page usage
- Enable transparent huge pages always
- Enable transparent huge pages only on madvised regions
- Disable transparent huge pages
- --thp-khugepaged-pages <pages to scan>
- Configure the number of pages that khugepaged should scan on each pass
- --thp-khugepaged-scan-sleep <milliseconds>
- Configure how many milliseconds khugepaged should wait between passes
- --thp-khugepages-alloc-sleep <milliseconds>
- Configure how many milliseconds khugepaged should wait after failing to allocate a huge page to throttle the next attempt.
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.
libhugetlbfs was written by various people on the libhugetlbfs-devel mailing list.