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authorHugh Dickins <hughd@google.com>2016-12-12 16:44:50 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2016-12-12 18:55:09 -0800
commit49920d28781dcced10cd30cb9a938e7d045a1c94 (patch)
treeb972f988f97c0b9180fe8e00dee4c8941dc32aef /Documentation
parenta66c0410b97c07a5708881198528ce724f7a3226 (diff)
mm: make transparent hugepage size public
Test programs want to know the size of a transparent hugepage. While it is commonly the same as the size of a hugetlbfs page (shown as Hugepagesize in /proc/meminfo), that is not always so: powerpc implements transparent hugepages in a different way from hugetlbfs pages, so it's coincidence when their sizes are the same; and x86 and others can support more than one hugetlbfs page size. Add /sys/kernel/mm/transparent_hugepage/hpage_pmd_size to show the THP size in bytes - it's the same for Anonymous and Shmem hugepages. Call it hpage_pmd_size (after HPAGE_PMD_SIZE) rather than hpage_size, in case some transparent support for pud and pgd pages is added later. Link: http://lkml.kernel.org/r/alpine.LSU.2.11.1612052200290.13021@eggly.anvils Signed-off-by: Hugh Dickins <hughd@google.com> Acked-by: Michal Hocko <mhocko@suse.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Greg Thelen <gthelen@google.com> Cc: David Rientjes <rientjes@google.com> Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> Cc: Andrea Arcangeli <aarcange@redhat.com> Cc: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Dan Williams <dan.j.williams@intel.com> Cc: Jan Kara <jack@suse.cz> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/vm/transhuge.txt5
1 files changed, 5 insertions, 0 deletions
diff --git a/Documentation/vm/transhuge.txt b/Documentation/vm/transhuge.txt
index 2ec6adb5a4ce..c4171e4519c2 100644
--- a/Documentation/vm/transhuge.txt
+++ b/Documentation/vm/transhuge.txt
@@ -136,6 +136,11 @@ or enable it back by writing 1:
echo 0 >/sys/kernel/mm/transparent_hugepage/use_zero_page
echo 1 >/sys/kernel/mm/transparent_hugepage/use_zero_page
+Some userspace (such as a test program, or an optimized memory allocation
+library) may want to know the size (in bytes) of a transparent hugepage:
+
+cat /sys/kernel/mm/transparent_hugepage/hpage_pmd_size
+
khugepaged will be automatically started when
transparent_hugepage/enabled is set to "always" or "madvise, and it'll
be automatically shutdown if it's set to "never".