admin-guide/mm/hugetlbpage.rst

9 the Linux kernel.  This support is built on top of multiple page size support
13 256M and ppc64 supports 4K and 16M.  A TLB is a cache of virtual-to-physical
19 Users can use the huge page support in Linux kernel by either using the mmap
22 First the Linux kernel needs to be built with the CONFIG_HUGETLBFS
28 persistent hugetlb pages in the kernel's huge page pool.  It also displays
73         ``/sys/kernel/mm/hugepages`` (described below).
77 configured in the kernel.
80 pages in the kernel's huge page pool.  "Persistent" huge pages will be
89 Pages that are used as huge pages are reserved inside the kernel and cannot
93 Once a number of huge pages have been pre-allocated to the kernel huge page
98 The administrator can allocate persistent huge pages on the kernel boot
158 	Note that this parameter only applies to non-gigantic huge pages.
179 indicates the current number of pre-allocated huge pages of the default size.
188 On a NUMA platform, the kernel will attempt to distribute the huge page pool
189 over all the set of allowed nodes specified by the NUMA memory policy of the
190 task that modifies ``nr_hugepages``. The default for the allowed nodes--when the
191 task has default memory policy--is all on-line nodes with memory.  Allowed
195 of the interaction of task memory policy, cpusets and per node attributes
200 allocation attempt.  If the kernel is unable to allocate huge pages from
206 init files.  This will enable the kernel to allocate huge pages early in
216 requested by applications.  Writing any non-zero value into this file
218 number of "surplus" huge pages from the kernel's normal page pool, when the
220 unused, they are freed back to the kernel's normal page pool.
229 smaller value.  The kernel will attempt to balance the freeing of huge pages
230 across all nodes in the memory policy of the task modifying ``nr_hugepages``.
231 Any free huge pages on the selected nodes will be freed back to the kernel's
236 of the in-use huge pages to surplus huge pages.  This will occur even if
238 this condition holds--that is, until ``nr_hugepages+nr_overcommit_hugepages`` is
239 increased sufficiently, or the surplus huge pages go out of use and are freed--
242 With support for multiple huge page pools at run-time available, much of
248 	/sys/kernel/mm/hugepages
250 For each huge page size supported by the running kernel, a subdirectory
253 	hugepages-${size}kB
290 demote_size) function as described above for the default huge page-sized case.
294 Interaction of Task Memory Policy with Huge Page Allocation/Freeing
300 NUMA memory policy of the task that modifies the ``nr_hugepages_mempolicy``
304 The recommended method to allocate or free huge pages to/from the kernel
307     numactl --interleave <node-list> echo 20 \
312     numactl -m <node-list> echo 20 >/proc/sys/vm/nr_hugepages_mempolicy
314 This will allocate or free ``abs(20 - nr_hugepages)`` to or from the nodes
315 specified in <node-list>, depending on whether number of persistent huge pages
317 allocated nor freed on any node not included in the specified <node-list>.
320 memory policy mode--bind, preferred, local or interleave--may be used.  The
324    Documentation/admin-guide/mm/numa_memory_policy.rst],
327    However, if a node in the policy does not contain sufficient contiguous
332    the task's memory policy.
334 #. One or more nodes may be specified with the bind or interleave policy.
335    If more than one node is specified with the preferred policy, only the
336    lowest numeric id will be used.  Local policy will select the node where
338    For local policy to be deterministic, the task must be bound to a cpu or
341    indeterminate.  Thus, local policy is not very useful for this purpose.
344 #. The nodes allowed mask will be derived from any non-default task mempolicy,
345    whether this policy was set explicitly by the task itself or one of its
347    shell with non-default policy, that policy will be used.  One can specify a
348    node list of "all" with numactl --interleave or --membind [-m] to achieve
351 #. Any task mempolicy specified--e.g., using numactl--will be constrained by
353    be no way for a task with non-default policy running in a cpuset with a
357 #. Boot-time huge page allocation attempts to distribute the requested number
358    of huge pages over all on-lines nodes with memory.
367 	/sys/devices/system/node/node[0-9]*/hugepages/
376 The free\_' and surplus\_' attribute files are read-only.  They return the number
389 The hugetlb may be migrated between the per-node hugepages pool in the following
394 hugetlb migration, that means these 3 cases can break the per-node hugepages pool.
405   mount -t hugetlbfs \
406 	-o uid=<value>,gid=<value>,mode=<value>,pagesize=<value>,size=<value>,\
481 ``hugepage-shm``
482 	see tools/testing/selftests/mm/hugepage-shm.c
484 ``hugepage-mmap``
485 	see tools/testing/selftests/mm/hugepage-mmap.c