Re: [PATCH V2 4/4] hugetlbfs: document min_size mount option

[Andrew Morton <akpm@linux-foundation.org>]

On Mon, 16 Mar 2015 16:53:29 -0700 Mike Kravetz <mike.kravetz@oracle.com> wrote:

> Update documentation for the hugetlbfs min_size mount option.
> 
> Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com>
> ---
>  Documentation/vm/hugetlbpage.txt | 21 ++++++++++++++-------
>  1 file changed, 14 insertions(+), 7 deletions(-)
> 
> diff --git a/Documentation/vm/hugetlbpage.txt b/Documentation/vm/hugetlbpage.txt
> index f2d3a10..83c0305 100644
> --- a/Documentation/vm/hugetlbpage.txt
> +++ b/Documentation/vm/hugetlbpage.txt
> @@ -267,8 +267,8 @@ call, then it is required that system administrator mount a file system of
>  type hugetlbfs:
>  
>    mount -t hugetlbfs \
> -	-o uid=<value>,gid=<value>,mode=<value>,size=<value>,nr_inodes=<value> \
> -	none /mnt/huge
> +	-o uid=<value>,gid=<value>,mode=<value>,size=<value>,min_size=<value>, \
> +	nr_inodes=<value> none /mnt/huge
>  
>  This command mounts a (pseudo) filesystem of type hugetlbfs on the directory
>  /mnt/huge.  Any files created on /mnt/huge uses huge pages.  The uid and gid
> @@ -277,11 +277,18 @@ the uid and gid of the current process are taken.  The mode option sets the
>  mode of root of file system to value & 01777.  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_inodes sets the maximum number of
> -inodes that /mnt/huge can use.  If the size or nr_inodes option is 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.
> +rounded down to HPAGE_SIZE.  The min_size option sets the minimum value of
> +memory (huge pages) allowed for the filesystem.  Like the size option,
> +min_size is rounded down to HPAGE_SIZE.  At mount time, the number of huge
> +pages specified by min_size are reserved for use by the filesystem.  If
> +there are not enough free huge pages available, the mount will fail.  As
> +huge pages are allocated to the filesystem and freed, the reserve count
> +is adjusted so that the sum of allocated and reserved huge pages is always
> +at least min_size.  The option nr_inodes sets the maximum number of
> +inodes that /mnt/huge can use.  If the size, min_size or nr_inodes option
> +is not provided on command line then no limits are set.  For size, min_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.

Nowhere here is the reader told the units of "size".  We should at
least describe that, and maybe even rename the thing to min_bytes.