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Signed-off-by: Mike Kravetz --- Documentation/admin-guide/mm/hugetlbpage.rst | 29 ++++++++++++++++++-- 1 file changed, 27 insertions(+), 2 deletions(-) diff --git a/Documentation/admin-guide/mm/hugetlbpage.rst b/Documentation= /admin-guide/mm/hugetlbpage.rst index 8abaeb144e44..902059a0257b 100644 --- a/Documentation/admin-guide/mm/hugetlbpage.rst +++ b/Documentation/admin-guide/mm/hugetlbpage.rst @@ -234,8 +234,12 @@ will exist, of the form:: =20 hugepages-${size}kB =20 -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 will exist:: =20 + demote + demote_size nr_hugepages nr_hugepages_mempolicy nr_overcommit_hugepages @@ -243,7 +247,28 @@ Inside each of these directories, the same set of fi= les will exist:: resv_hugepages surplus_hugepages =20 -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. The demote interfaces are: + +demote_size + is the size of demoted pages. When a page is demoted a correspo= nding + number of huge pages of demote_size will be created. For huge p= ages + of the smallest supported size (2MB on x86), demote_size will be= the + system page size (PAGE_SIZE). If demote_size is the system page= size + then demoting a page will simply free the huge page. demote_siz= e is + a read only interface. + +demote + is used to demote a number of huge pages. A user with root priv= ileges + can write to this file. It may not be possible to demote the + requested number of huge pages. To determine how many pages wer= e + actually demoted, compare the value of nr_hugepages before and a= fter + writing to the demote interface. demote is a write only interfa= ce. + +The interfaces which are the same as in ``/proc`` function as described +above for the default huge page-sized case. =20 .. _mem_policy_and_hp_alloc: =20 --=20 2.31.1