[PATCH] hugetlbfs doc. update

the configured hugepage size - this is needed for generating the proper

alignment and size of the arguments to the above system calls.

The output of "cat /proc/meminfo" will have output like:

The output of "cat /proc/meminfo" will have lines like:

.....

HugePages_Total: xxx

pre-configured) hugepages.

The allocation (or deallocation) of hugetlb pages is possible only if there are

enough physically contiguous free pages in system (freeing of hugepages is

possible only if there are enough hugetlb pages free that can be transfered

possible only if there are enough hugetlb pages free that can be transferred

back to regular memory pool).

Pages that are used as hugetlb pages are reserved inside the kernel and can

not be used for other purposes.

Pages that are used as hugetlb pages are reserved inside the kernel and cannot

be used for other purposes.

Once the kernel with Hugetlb page support is built and running, a user can

use either the mmap system call or shared memory system calls to start using

This command will try to configure 20 hugepages in the system.  The success

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 file.  This will enable the

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).

mode of root of file system to value & 0777.  This value is given in octal.

By default the value 0755 is picked. The size option sets the maximum value of

memory (huge pages) allowed for that filesystem (/mnt/huge). The size is

rounded down to HPAGE_SIZE.  The option nr_inode sets the maximum number of

inodes that /mnt/huge can use.  If the size or nr_inode options are not

rounded down to HPAGE_SIZE.  The option nr_inodes sets the maximum number of

inodes that /mnt/huge can use.  If the size or nr_inodes options are not

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. An example is given at

read and write system calls are not supported on files that reside on hugetlb

file systems.

A regular chown, chgrp and chmod commands (with right permissions) could be

Regular chown, chgrp, and chmod commands (with right permissions) could be

used to change the file attributes on hugetlbfs.

Also, it is important to note that no such mount command is required if the

wish to use hugetlb page via shared memory segment should be a member of

a supplementary group and system admin needs to configure that gid into

/proc/sys/vm/hugetlb_shm_group.  It is possible for same or different

applications to use any combination of mmaps and shm* calls.  Though the

mount of filesystem will be required for using mmaps.

applications to use any combination of mmaps and shm* calls, though the

mount of filesystem will be required for using mmap calls.

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