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docs/vm: hugetlbpage.txt: convert to ReST format
Signed-off-by: Mike Rapoport <rppt@linux.vnet.ibm.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Mike Rapoport
Jonathan Corbet
parent
aa9f34e5da
commit
148723f711
@ -1,3 +1,11 @@
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.. _hugetlbpage:
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=============
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HugeTLB Pages
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=============
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Overview
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========
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The intent of this file is to give a brief summary of hugetlbpage support in
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the Linux kernel. This support is built on top of multiple page size support
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@ -18,53 +26,59 @@ First the Linux kernel needs to be built with the CONFIG_HUGETLBFS
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automatically when CONFIG_HUGETLBFS is selected) configuration
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options.
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The /proc/meminfo file provides information about the total number of
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The ``/proc/meminfo`` file provides information about the total number of
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persistent hugetlb pages in the kernel's huge page pool. It also displays
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default huge page size and information about the number of free, reserved
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and surplus huge pages in the pool of huge pages of default size.
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The huge page size is needed for generating the proper alignment and
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size of the arguments to system calls that map huge page regions.
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The output of "cat /proc/meminfo" will include lines like:
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The output of ``cat /proc/meminfo`` will include lines like::
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.....
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HugePages_Total: uuu
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HugePages_Free: vvv
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HugePages_Rsvd: www
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HugePages_Surp: xxx
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Hugepagesize: yyy kB
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Hugetlb: zzz kB
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HugePages_Total: uuu
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HugePages_Free: vvv
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HugePages_Rsvd: www
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HugePages_Surp: xxx
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Hugepagesize: yyy kB
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Hugetlb: zzz kB
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where:
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HugePages_Total is the size of the pool of huge pages.
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HugePages_Free is the number of huge pages in the pool that are not yet
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allocated.
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HugePages_Rsvd is short for "reserved," and is the number of huge pages for
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which a commitment to allocate from the pool has been made,
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but no allocation has yet been made. Reserved huge pages
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guarantee that an application will be able to allocate a
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huge page from the pool of huge pages at fault time.
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HugePages_Surp is short for "surplus," and is the number of huge pages in
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the pool above the value in /proc/sys/vm/nr_hugepages. The
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maximum number of surplus huge pages is controlled by
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/proc/sys/vm/nr_overcommit_hugepages.
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Hugepagesize is the default hugepage size (in Kb).
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Hugetlb is the total amount of memory (in kB), consumed by huge
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pages of all sizes.
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If huge pages of different sizes are in use, this number
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will exceed HugePages_Total * Hugepagesize. To get more
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detailed information, please, refer to
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/sys/kernel/mm/hugepages (described below).
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HugePages_Total
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is the size of the pool of huge pages.
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HugePages_Free
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is the number of huge pages in the pool that are not yet
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allocated.
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HugePages_Rsvd
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is short for "reserved," and is the number of huge pages for
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which a commitment to allocate from the pool has been made,
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but no allocation has yet been made. Reserved huge pages
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guarantee that an application will be able to allocate a
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huge page from the pool of huge pages at fault time.
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HugePages_Surp
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is short for "surplus," and is the number of huge pages in
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the pool above the value in ``/proc/sys/vm/nr_hugepages``. The
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maximum number of surplus huge pages is controlled by
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``/proc/sys/vm/nr_overcommit_hugepages``.
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Hugepagesize
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is the default hugepage size (in Kb).
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Hugetlb
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is the total amount of memory (in kB), consumed by huge
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pages of all sizes.
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If huge pages of different sizes are in use, this number
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will exceed HugePages_Total \* Hugepagesize. To get more
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detailed information, please, refer to
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``/sys/kernel/mm/hugepages`` (described below).
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/proc/filesystems should also show a filesystem of type "hugetlbfs" configured
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in the kernel.
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``/proc/filesystems`` should also show a filesystem of type "hugetlbfs"
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configured in the kernel.
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/proc/sys/vm/nr_hugepages indicates the current number of "persistent" huge
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``/proc/sys/vm/nr_hugepages`` indicates the current number of "persistent" huge
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pages in the kernel's huge page pool. "Persistent" huge pages will be
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returned to the huge page pool when freed by a task. A user with root
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privileges can dynamically allocate more or free some persistent huge pages
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by increasing or decreasing the value of 'nr_hugepages'.
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by increasing or decreasing the value of ``nr_hugepages``.
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Pages that are used as huge pages are reserved inside the kernel and cannot
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be used for other purposes. Huge pages cannot be swapped out under
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@ -86,10 +100,10 @@ with a huge page size selection parameter "hugepagesz=<size>". <size> must
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be specified in bytes with optional scale suffix [kKmMgG]. The default huge
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page size may be selected with the "default_hugepagesz=<size>" boot parameter.
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When multiple huge page sizes are supported, /proc/sys/vm/nr_hugepages
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When multiple huge page sizes are supported, ``/proc/sys/vm/nr_hugepages``
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indicates the current number of pre-allocated huge pages of the default size.
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Thus, one can use the following command to dynamically allocate/deallocate
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default sized persistent huge pages:
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default sized persistent huge pages::
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echo 20 > /proc/sys/vm/nr_hugepages
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@ -98,7 +112,7 @@ huge page pool to 20, allocating or freeing huge pages, as required.
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On a NUMA platform, the kernel will attempt to distribute the huge page pool
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over all the set of allowed nodes specified by the NUMA memory policy of the
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task that modifies nr_hugepages. The default for the allowed nodes--when the
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task that modifies ``nr_hugepages``. The default for the allowed nodes--when the
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task has default memory policy--is all on-line nodes with memory. Allowed
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nodes with insufficient available, contiguous memory for a huge page will be
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silently skipped when allocating persistent huge pages. See the discussion
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@ -117,51 +131,52 @@ init files. This will enable the kernel to allocate huge pages early in
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the boot process when the possibility of getting physical contiguous pages
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is still very high. Administrators can verify the number of huge pages
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actually allocated by checking the sysctl or meminfo. To check the per node
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distribution of huge pages in a NUMA system, use:
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distribution of huge pages in a NUMA system, use::
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cat /sys/devices/system/node/node*/meminfo | fgrep Huge
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/proc/sys/vm/nr_overcommit_hugepages specifies how large the pool of
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huge pages can grow, if more huge pages than /proc/sys/vm/nr_hugepages are
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``/proc/sys/vm/nr_overcommit_hugepages`` specifies how large the pool of
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huge pages can grow, if more huge pages than ``/proc/sys/vm/nr_hugepages`` are
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requested by applications. Writing any non-zero value into this file
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indicates that the hugetlb subsystem is allowed to try to obtain that
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number of "surplus" huge pages from the kernel's normal page pool, when the
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persistent huge page pool is exhausted. As these surplus huge pages become
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unused, they are freed back to the kernel's normal page pool.
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When increasing the huge page pool size via nr_hugepages, any existing surplus
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pages will first be promoted to persistent huge pages. Then, additional
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When increasing the huge page pool size via ``nr_hugepages``, any existing
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surplus pages will first be promoted to persistent huge pages. Then, additional
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huge pages will be allocated, if necessary and if possible, to fulfill
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the new persistent huge page pool size.
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The administrator may shrink the pool of persistent huge pages for
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the default huge page size by setting the nr_hugepages sysctl to a
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the default huge page size by setting the ``nr_hugepages`` sysctl to a
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smaller value. The kernel will attempt to balance the freeing of huge pages
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across all nodes in the memory policy of the task modifying nr_hugepages.
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across all nodes in the memory policy of the task modifying ``nr_hugepages``.
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Any free huge pages on the selected nodes will be freed back to the kernel's
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normal page pool.
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Caveat: Shrinking the persistent huge page pool via nr_hugepages such that
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Caveat: Shrinking the persistent huge page pool via ``nr_hugepages`` such that
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it becomes less than the number of huge pages in use will convert the balance
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of the in-use huge pages to surplus huge pages. This will occur even if
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the number of surplus pages it would exceed the overcommit value. As long as
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this condition holds--that is, until nr_hugepages+nr_overcommit_hugepages is
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this condition holds--that is, until ``nr_hugepages+nr_overcommit_hugepages`` is
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increased sufficiently, or the surplus huge pages go out of use and are freed--
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no more surplus huge pages will be allowed to be allocated.
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With support for multiple huge page pools at run-time available, much of
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the huge page userspace interface in /proc/sys/vm has been duplicated in sysfs.
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The /proc interfaces discussed above have been retained for backwards
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compatibility. The root huge page control directory in sysfs is:
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the huge page userspace interface in ``/proc/sys/vm`` has been duplicated in
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sysfs.
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The ``/proc`` interfaces discussed above have been retained for backwards
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compatibility. The root huge page control directory in sysfs is::
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/sys/kernel/mm/hugepages
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For each huge page size supported by the running kernel, a subdirectory
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will exist, of the form:
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will exist, of the form::
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hugepages-${size}kB
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Inside each of these directories, the same set of files will exist:
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Inside each of these directories, the same set of files will exist::
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nr_hugepages
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nr_hugepages_mempolicy
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@ -176,33 +191,33 @@ which function as described above for the default huge page-sized case.
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Interaction of Task Memory Policy with Huge Page Allocation/Freeing
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===================================================================
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Whether huge pages are allocated and freed via the /proc interface or
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the /sysfs interface using the nr_hugepages_mempolicy attribute, the NUMA
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nodes from which huge pages are allocated or freed are controlled by the
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NUMA memory policy of the task that modifies the nr_hugepages_mempolicy
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sysctl or attribute. When the nr_hugepages attribute is used, mempolicy
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Whether huge pages are allocated and freed via the ``/proc`` interface or
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the ``/sysfs`` interface using the ``nr_hugepages_mempolicy`` attribute, the
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NUMA nodes from which huge pages are allocated or freed are controlled by the
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NUMA memory policy of the task that modifies the ``nr_hugepages_mempolicy``
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sysctl or attribute. When the ``nr_hugepages`` attribute is used, mempolicy
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is ignored.
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The recommended method to allocate or free huge pages to/from the kernel
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huge page pool, using the nr_hugepages example above, is:
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huge page pool, using the ``nr_hugepages`` example above, is::
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numactl --interleave <node-list> echo 20 \
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>/proc/sys/vm/nr_hugepages_mempolicy
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or, more succinctly:
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or, more succinctly::
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numactl -m <node-list> echo 20 >/proc/sys/vm/nr_hugepages_mempolicy
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This will allocate or free abs(20 - nr_hugepages) to or from the nodes
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This will allocate or free ``abs(20 - nr_hugepages)`` to or from the nodes
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specified in <node-list>, depending on whether number of persistent huge pages
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is initially less than or greater than 20, respectively. No huge pages will be
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allocated nor freed on any node not included in the specified <node-list>.
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When adjusting the persistent hugepage count via nr_hugepages_mempolicy, any
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When adjusting the persistent hugepage count via ``nr_hugepages_mempolicy``, any
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memory policy mode--bind, preferred, local or interleave--may be used. The
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resulting effect on persistent huge page allocation is as follows:
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1) Regardless of mempolicy mode [see Documentation/vm/numa_memory_policy.txt],
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#. Regardless of mempolicy mode [see Documentation/vm/numa_memory_policy.txt],
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persistent huge pages will be distributed across the node or nodes
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specified in the mempolicy as if "interleave" had been specified.
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However, if a node in the policy does not contain sufficient contiguous
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@ -212,7 +227,7 @@ resulting effect on persistent huge page allocation is as follows:
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possibly, allocation of persistent huge pages on nodes not allowed by
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the task's memory policy.
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2) One or more nodes may be specified with the bind or interleave policy.
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#. One or more nodes may be specified with the bind or interleave policy.
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If more than one node is specified with the preferred policy, only the
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lowest numeric id will be used. Local policy will select the node where
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the task is running at the time the nodes_allowed mask is constructed.
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@ -222,20 +237,20 @@ resulting effect on persistent huge page allocation is as follows:
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indeterminate. Thus, local policy is not very useful for this purpose.
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Any of the other mempolicy modes may be used to specify a single node.
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3) The nodes allowed mask will be derived from any non-default task mempolicy,
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#. The nodes allowed mask will be derived from any non-default task mempolicy,
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whether this policy was set explicitly by the task itself or one of its
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ancestors, such as numactl. This means that if the task is invoked from a
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shell with non-default policy, that policy will be used. One can specify a
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node list of "all" with numactl --interleave or --membind [-m] to achieve
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interleaving over all nodes in the system or cpuset.
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4) Any task mempolicy specified--e.g., using numactl--will be constrained by
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#. Any task mempolicy specified--e.g., using numactl--will be constrained by
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the resource limits of any cpuset in which the task runs. Thus, there will
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be no way for a task with non-default policy running in a cpuset with a
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subset of the system nodes to allocate huge pages outside the cpuset
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without first moving to a cpuset that contains all of the desired nodes.
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5) Boot-time huge page allocation attempts to distribute the requested number
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#. Boot-time huge page allocation attempts to distribute the requested number
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of huge pages over all on-lines nodes with memory.
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Per Node Hugepages Attributes
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@ -243,22 +258,22 @@ Per Node Hugepages Attributes
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A subset of the contents of the root huge page control directory in sysfs,
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described above, will be replicated under each the system device of each
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NUMA node with memory in:
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NUMA node with memory in::
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/sys/devices/system/node/node[0-9]*/hugepages/
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Under this directory, the subdirectory for each supported huge page size
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contains the following attribute files:
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contains the following attribute files::
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nr_hugepages
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free_hugepages
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surplus_hugepages
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The free_' and surplus_' attribute files are read-only. They return the number
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The free\_' and surplus\_' attribute files are read-only. They return the number
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of free and surplus [overcommitted] huge pages, respectively, on the parent
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node.
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The nr_hugepages attribute returns the total number of huge pages on the
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The ``nr_hugepages`` attribute returns the total number of huge pages on the
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specified node. When this attribute is written, the number of persistent huge
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pages on the parent node will be adjusted to the specified value, if sufficient
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resources exist, regardless of the task's mempolicy or cpuset constraints.
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@ -273,37 +288,51 @@ Using Huge Pages
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If the user applications are going to request huge pages using mmap system
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call, then it is required that system administrator mount a file system of
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type hugetlbfs:
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type hugetlbfs::
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mount -t hugetlbfs \
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-o uid=<value>,gid=<value>,mode=<value>,pagesize=<value>,size=<value>,\
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min_size=<value>,nr_inodes=<value> none /mnt/huge
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This command mounts a (pseudo) filesystem of type hugetlbfs on the directory
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/mnt/huge. Any files created on /mnt/huge uses huge pages. The uid and gid
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options sets the owner and group of the root of the file system. By default
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the uid and gid of the current process are taken. The mode option sets the
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mode of root of file system to value & 01777. This value is given in octal.
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By default the value 0755 is picked. If the platform supports multiple huge
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page sizes, the pagesize option can be used to specify the huge page size and
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associated pool. pagesize is specified in bytes. If pagesize is not specified
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the platform's default huge page size and associated pool will be used. The
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size option sets the maximum value of memory (huge pages) allowed for that
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filesystem (/mnt/huge). The size option can be specified in bytes, or as a
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percentage of the specified huge page pool (nr_hugepages). The size is
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rounded down to HPAGE_SIZE boundary. The min_size option sets the minimum
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value of memory (huge pages) allowed for the filesystem. min_size can be
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specified in the same way as size, either bytes or a percentage of the
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huge page pool. At mount time, the number of huge pages specified by
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min_size are reserved for use by the filesystem. If there are not enough
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free huge pages available, the mount will fail. As huge pages are allocated
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to the filesystem and freed, the reserve count is adjusted so that the sum
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of allocated and reserved huge pages is always at least min_size. The option
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nr_inodes sets the maximum number of inodes that /mnt/huge can use. If the
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size, min_size or nr_inodes option is not provided on command line then
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no limits are set. For pagesize, size, min_size and nr_inodes options, you
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can use [G|g]/[M|m]/[K|k] to represent giga/mega/kilo. For example, size=2K
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has the same meaning as size=2048.
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``/mnt/huge``. Any files created on ``/mnt/huge`` uses huge pages.
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The ``uid`` and ``gid`` options sets the owner and group of the root of the
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file system. By default the ``uid`` and ``gid`` of the current process
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are taken.
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The ``mode`` option sets the mode of root of file system to value & 01777.
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This value is given in octal. By default the value 0755 is picked.
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If the platform supports multiple huge page sizes, the ``pagesize`` option can
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be used to specify the huge page size and associated pool. ``pagesize``
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is specified in bytes. If ``pagesize`` is not specified the platform's
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default huge page size and associated pool will be used.
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The ``size`` option sets the maximum value of memory (huge pages) allowed
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for that filesystem (``/mnt/huge``). The ``size`` option can be specified
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in bytes, or as a percentage of the specified huge page pool (``nr_hugepages``).
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The size is rounded down to HPAGE_SIZE boundary.
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The ``min_size`` option sets the minimum value of memory (huge pages) allowed
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for the filesystem. ``min_size`` can be specified in the same way as ``size``,
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either bytes or a percentage of the huge page pool.
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At mount time, the number of huge pages specified by ``min_size`` are reserved
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for use by the filesystem.
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If there are not enough free huge pages available, the mount will fail.
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As huge pages are allocated to the filesystem and freed, the reserve count
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is adjusted so that the sum of allocated and reserved huge pages is always
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at least ``min_size``.
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The option ``nr_inodes`` sets the maximum number of inodes that ``/mnt/huge``
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can use.
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If the ``size``, ``min_size`` or ``nr_inodes`` option is not provided on
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command line then no limits are set.
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For ``pagesize``, ``size``, ``min_size`` and ``nr_inodes`` options, you can
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use [G|g]/[M|m]/[K|k] to represent giga/mega/kilo.
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For example, size=2K has the same meaning as size=2048.
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While read system calls are supported on files that reside on hugetlb
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file systems, write system calls are not.
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@ -313,12 +342,12 @@ used to change the file attributes on hugetlbfs.
|
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Also, it is important to note that no such mount command is required if
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applications are going to use only shmat/shmget system calls or mmap with
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MAP_HUGETLB. For an example of how to use mmap with MAP_HUGETLB see map_hugetlb
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below.
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MAP_HUGETLB. For an example of how to use mmap with MAP_HUGETLB see
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:ref:`map_hugetlb <map_hugetlb>` below.
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||||
|
||||
Users who wish to use hugetlb memory via shared memory segment should be a
|
||||
member of a supplementary group and system admin needs to configure that gid
|
||||
into /proc/sys/vm/hugetlb_shm_group. It is possible for same or different
|
||||
into ``/proc/sys/vm/hugetlb_shm_group``. It is possible for same or different
|
||||
applications to use any combination of mmaps and shm* calls, though the mount of
|
||||
filesystem will be required for using mmap calls without MAP_HUGETLB.
|
||||
|
||||
@ -332,15 +361,21 @@ a hugetlb page and the length is smaller than the hugepage size.
|
||||
Examples
|
||||
========
|
||||
|
||||
1) map_hugetlb: see tools/testing/selftests/vm/map_hugetlb.c
|
||||
.. _map_hugetlb:
|
||||
|
||||
2) hugepage-shm: see tools/testing/selftests/vm/hugepage-shm.c
|
||||
``map_hugetlb``
|
||||
see tools/testing/selftests/vm/map_hugetlb.c
|
||||
|
||||
3) hugepage-mmap: see tools/testing/selftests/vm/hugepage-mmap.c
|
||||
``hugepage-shm``
|
||||
see tools/testing/selftests/vm/hugepage-shm.c
|
||||
|
||||
4) The libhugetlbfs (https://github.com/libhugetlbfs/libhugetlbfs) library
|
||||
provides a wide range of userspace tools to help with huge page usability,
|
||||
environment setup, and control.
|
||||
``hugepage-mmap``
|
||||
see tools/testing/selftests/vm/hugepage-mmap.c
|
||||
|
||||
The `libhugetlbfs`_ library provides a wide range of userspace tools
|
||||
to help with huge page usability, environment setup, and control.
|
||||
|
||||
.. _libhugetlbfs: https://github.com/libhugetlbfs/libhugetlbfs
|
||||
|
||||
Kernel development regression testing
|
||||
=====================================
|
||||
|
||||
Loading…
Reference in New Issue
Block a user