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diff --git a/Documentation/admin-guide/mm/hugetlbpage.rst b/Documentation/admin-guide/mm/hugetlbpage.rst index 1cc0bc78d10e..5026e58826e2 100644 --- a/Documentation/admin-guide/mm/hugetlbpage.rst +++ b/Documentation/admin-guide/mm/hugetlbpage.rst @@ -100,6 +100,41 @@ with a huge page size selection parameter "hugepagesz=<size>". <size> must be specified in bytes with optional scale suffix [kKmMgG]. The default huge page size may be selected with the "default_hugepagesz=<size>" boot parameter. +Hugetlb boot command line parameter semantics +hugepagesz - Specify a huge page size. Used in conjunction with hugepages + parameter to preallocate a number of huge pages of the specified + size. Hence, hugepagesz and hugepages are typically specified in + pairs such as: + hugepagesz=2M hugepages=512 + hugepagesz can only be specified once on the command line for a + specific huge page size. Valid huge page sizes are architecture + dependent. +hugepages - Specify the number of huge pages to preallocate. This typically + follows a valid hugepagesz or default_hugepagesz parameter. However, + if hugepages is the first or only hugetlb command line parameter it + 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. + For example, on an architecture with 2M default huge page size: + hugepages=256 hugepagesz=2M hugepages=512 + will result in 256 2M huge pages being allocated and a warning message + indicating that the hugepages=512 parameter is ignored. If a hugepages + parameter is preceded by an invalid hugepagesz parameter, it 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 + optionally be followed by the hugepages parameter to preallocate a + specific number of huge pages of default size. The number of default + sized huge pages to preallocate can also be implicitly specified as + mentioned in the hugepages section above. Therefore, on an + architecture with 2M default huge page size: + hugepages=256 + default_hugepagesz=2M hugepages=256 + hugepages=256 default_hugepagesz=2M + will all result in 256 2M huge pages being allocated. Valid default + huge page size is architecture dependent. + 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. Thus, one can use the following command to dynamically allocate/deallocate |