Commit d5dbac87 authored by Nishanth Aravamudan's avatar Nishanth Aravamudan Committed by Linus Torvalds

Documentation: update hugetlb information

The hugetlb documentation has gotten a bit out of sync with the current code.
Updated the sysctl file to refer to Documentation/vm/hugetlbpage.txt.  Update
that file to contain the current state of affairs (with the newer named sysctl
in place).
Signed-off-by: default avatarNishanth Aravamudan <nacc@us.ibm.com>
Acked-by: default avatarAdam Litke <agl@us.ibm.com>
Cc: William Lee Irwin III <wli@holomorphy.com>
Cc: Dave Hansen <haveblue@us.ibm.com>
Cc: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 368d2c63
......@@ -34,6 +34,8 @@ Currently, these files are in /proc/sys/vm:
- oom_kill_allocating_task
- mmap_min_address
- numa_zonelist_order
- nr_hugepages
- nr_overcommit_hugepages
==============================================================
......@@ -305,3 +307,20 @@ will select "node" order in following case.
Otherwise, "zone" order will be selected. Default order is recommended unless
this is causing problems for your system/application.
==============================================================
nr_hugepages
Change the minimum size of the hugepage pool.
See Documentation/vm/hugetlbpage.txt
==============================================================
nr_overcommit_hugepages
Change the maximum size of the hugepage pool. The maximum is
nr_hugepages + nr_overcommit_hugepages.
See Documentation/vm/hugetlbpage.txt
......@@ -30,9 +30,10 @@ alignment and size of the arguments to the above system calls.
The output of "cat /proc/meminfo" will have lines like:
.....
HugePages_Total: xxx
HugePages_Free: yyy
HugePages_Rsvd: www
HugePages_Total: vvv
HugePages_Free: www
HugePages_Rsvd: xxx
HugePages_Surp: yyy
Hugepagesize: zzz kB
where:
......@@ -42,6 +43,10 @@ allocated.
HugePages_Rsvd is short for "reserved," and is the number of hugepages
for which a commitment to allocate from the pool has been made, but no
allocation has yet been made. It's vaguely analogous to overcommit.
HugePages_Surp is short for "surplus," and is the number of hugepages in
the pool above the value in /proc/sys/vm/nr_hugepages. The maximum
number of surplus hugepages is controlled by
/proc/sys/vm/nr_overcommit_hugepages.
/proc/filesystems should also show a filesystem of type "hugetlbfs" configured
in the kernel.
......@@ -71,7 +76,25 @@ or failure of allocation depends on the amount of physically contiguous
memory that is preset in system at this time. System administrators may want
to put this command in one of the local rc init files. This will enable the
kernel to request huge pages early in the boot process (when the possibility
of getting physical contiguous pages is still very high).
of getting physical contiguous pages is still very high). In either
case, adminstrators will want to verify the number of hugepages actually
allocated by checking the sysctl or meminfo.
/proc/sys/vm/nr_overcommit_hugepages indicates how large the pool of
hugepages can grow, if more hugepages than /proc/sys/vm/nr_hugepages are
requested by applications. echo'ing any non-zero value into this file
indicates that the hugetlb subsystem is allowed to try to obtain
hugepages from the buddy allocator, if the normal pool is exhausted. As
these surplus hugepages go out of use, they are freed back to the buddy
allocator.
Caveat: Shrinking the pool via nr_hugepages while a surplus is in effect
will allow the number of surplus huge pages to exceed the overcommit
value, as the pool hugepages (which must have been in use for a surplus
hugepages to be allocated) will become surplus hugepages. As long as
this condition holds, however, no more surplus huge pages will be
allowed on the system until one of the two sysctls are increased
sufficiently, or the surplus huge pages go out of use and are freed.
If the user applications are going to request hugepages using mmap system
call, then it is required that system administrator mount a file system of
......@@ -94,8 +117,8 @@ provided on command line then no limits are set. For size and nr_inodes
options, you can use [G|g]/[M|m]/[K|k] to represent giga/mega/kilo. For
example, size=2K has the same meaning as size=2048.
read and write system calls are not supported on files that reside on hugetlb
file systems.
While read system calls are supported on files that reside on hugetlb
file systems, write system calls are not.
Regular chown, chgrp, and chmod commands (with right permissions) could be
used to change the file attributes on hugetlbfs.
......
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