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Diffstat (limited to 'Documentation/admin-guide/mm/hugetlbpage.rst')
| -rw-r--r-- | Documentation/admin-guide/mm/hugetlbpage.rst | 65 |
1 files changed, 55 insertions, 10 deletions
diff --git a/Documentation/admin-guide/mm/hugetlbpage.rst b/Documentation/admin-guide/mm/hugetlbpage.rst index f7b1c7462991..e4d4b4a8dc97 100644 --- a/Documentation/admin-guide/mm/hugetlbpage.rst +++ b/Documentation/admin-guide/mm/hugetlbpage.rst @@ -1,5 +1,3 @@ -.. _hugetlbpage: - ============= HugeTLB Pages ============= @@ -60,8 +58,12 @@ HugePages_Surp the pool above the value in ``/proc/sys/vm/nr_hugepages``. The maximum number of surplus huge pages is controlled by ``/proc/sys/vm/nr_overcommit_hugepages``. + Note: When the feature of freeing unused vmemmap pages associated + with each hugetlb page is enabled, the number of surplus huge pages + may be temporarily larger than the maximum number of surplus huge + pages when the system is under memory pressure. Hugepagesize - is the default hugepage size (in Kb). + is the default hugepage size (in kB). Hugetlb is the total amount of memory (in kB), consumed by huge pages of all sizes. @@ -80,6 +82,10 @@ returned to the huge page pool when freed by a task. A user with root privileges can dynamically allocate more or free some persistent huge pages by increasing or decreasing the value of ``nr_hugepages``. +Note: When the feature of freeing unused vmemmap pages associated with each +hugetlb page is enabled, we can fail to free the huge pages triggered by +the user when the system is under memory pressure. Please try again later. + Pages that are used as huge pages are reserved inside the kernel and cannot be used for other purposes. Huge pages cannot be swapped out under memory pressure. @@ -120,7 +126,9 @@ hugepages implicitly specifies the number of huge pages of default size to allocate. If the number of huge pages of default size is implicitly specified, it can not be overwritten by a hugepagesz,hugepages - parameter pair for the default size. + parameter pair for the default size. This parameter also has a + node format. The node format specifies the number of huge pages + to allocate on specific nodes. For example, on an architecture with 2M default huge page size:: @@ -130,6 +138,14 @@ hugepages indicating that the hugepages=512 parameter is ignored. If a hugepages parameter is preceded by an invalid hugepagesz parameter, it will be ignored. + + Node format example:: + + hugepagesz=2M hugepages=0:1,1:2 + + It will allocate 1 2M hugepage on node0 and 2 2M hugepages on node1. + If the node number is invalid, the parameter will be ignored. + default_hugepagesz Specify the default huge page size. This parameter can only be specified once on the command line. default_hugepagesz can @@ -145,6 +161,9 @@ default_hugepagesz will all result in 256 2M huge pages being allocated. Valid default huge page size is architecture dependent. +hugetlb_free_vmemmap + When CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP is set, this enables HugeTLB + Vmemmap Optimization (HVO). When multiple huge page sizes are supported, ``/proc/sys/vm/nr_hugepages`` indicates the current number of pre-allocated huge pages of the default size. @@ -223,8 +242,12 @@ will exist, of the form:: hugepages-${size}kB -Inside each of these directories, the same set of files will exist:: +Inside each of these directories, the set of files contained in ``/proc`` +will exist. In addition, two additional interfaces for demoting huge +pages may exist:: + demote + demote_size nr_hugepages nr_hugepages_mempolicy nr_overcommit_hugepages @@ -232,7 +255,29 @@ Inside each of these directories, the same set of files will exist:: resv_hugepages surplus_hugepages -which function as described above for the default huge page-sized case. +The demote interfaces provide the ability to split a huge page into +smaller huge pages. For example, the x86 architecture supports both +1GB and 2MB huge pages sizes. A 1GB huge page can be split into 512 +2MB huge pages. Demote interfaces are not available for the smallest +huge page size. The demote interfaces are: + +demote_size + is the size of demoted pages. When a page is demoted a corresponding + number of huge pages of demote_size will be created. By default, + demote_size is set to the next smaller huge page size. If there are + multiple smaller huge page sizes, demote_size can be set to any of + these smaller sizes. Only huge page sizes less than the current huge + pages size are allowed. + +demote + is used to demote a number of huge pages. A user with root privileges + can write to this file. It may not be possible to demote the + requested number of huge pages. To determine how many pages were + actually demoted, compare the value of nr_hugepages before and after + writing to the demote interface. demote is a write only interface. + +The interfaces which are the same as in ``/proc`` (all except demote and +demote_size) function as described above for the default huge page-sized case. .. _mem_policy_and_hp_alloc: @@ -266,7 +311,7 @@ memory policy mode--bind, preferred, local or interleave--may be used. The resulting effect on persistent huge page allocation is as follows: #. Regardless of mempolicy mode [see - :ref:`Documentation/admin-guide/mm/numa_memory_policy.rst <numa_memory_policy>`], + Documentation/admin-guide/mm/numa_memory_policy.rst], persistent huge pages will be distributed across the node or nodes specified in the mempolicy as if "interleave" had been specified. However, if a node in the policy does not contain sufficient contiguous @@ -414,13 +459,13 @@ Examples .. _map_hugetlb: ``map_hugetlb`` - see tools/testing/selftests/vm/map_hugetlb.c + see tools/testing/selftests/mm/map_hugetlb.c ``hugepage-shm`` - see tools/testing/selftests/vm/hugepage-shm.c + see tools/testing/selftests/mm/hugepage-shm.c ``hugepage-mmap`` - see tools/testing/selftests/vm/hugepage-mmap.c + see tools/testing/selftests/mm/hugepage-mmap.c The `libhugetlbfs`_ library provides a wide range of userspace tools to help with huge page usability, environment setup, and control. |