On 02/10/2012 01:20 PM, Dave Chinner wrote:
> On Fri, Feb 10, 2012 at 11:24:26AM +0800, Jeff Liu wrote:
>> On 02/10/2012 06:25 AM, Dave Chinner wrote:
>>> On Thu, Feb 09, 2012 at 10:27:05PM +0800, Jeff Liu wrote:
>>>> Strange, I also tried to build XFS with 2k which shown as following:
>>>> $ sudo mkfs.xfs -b size=2k -n size=2k -f /dev/sda7
>>>> $ xfs_info /dev/sda7
>>>> meta-data=/dev/sda7 isize=256 agcount=4, agsize=1418736
>>>> = sectsz=512 attr=2
>>>> data = bsize=2048 blocks=5674944, imaxpct=25
>>>> = sunit=0 swidth=0 blks
>>>> naming =version 2 bsize=2048 ascii-ci=0
>>>> log =internal bsize=2048 blocks=5120, version=2
>>> The block size for data, metadata, directories and the log is 2k,
>>> just like you asked.
>> Sorry, I mislead you.
>> Yes, the block size for data and metadata, etc are ok for me, but the
>> allocate unit at "struct stat.st_blksize" is 4k, It should match
>> data->bsize=2k IMHO.
> That field has nothing to do with the filesystem block size.
> According to the stat(2) man page:
> 'The st_blksize field gives the "preferred" blocksize for efficient
> file system I/O.'
> Giving a value of less than PAGE_SIZE for this field leads to
> inefficient IO because it forces the page cache to do
> read-modify-write cycles for single filesystem block writes. Hence
> on a 4k page size machine, it needs to report 4k as a minimum to
> avoid this. On a 64k page size machine, you'll find that value is
Sigh, I was misled by EXT4's output for stat(2), since its st_blksize is
2k which is equal to the mkfs formating value even on a 4k page size
> Indeed, XFS gives you some control over what is actually reported
> here. If your file lies on a real-time device, then XFS will export
> the extent allocation size (either the mkfs default of the per inode
> hint if it is set) in this field. For files on the data device, if
> you mount with the "largeio" mount option, XFS will export the
> stripe width if it is set, the biosize if that mount option is used
> or the PAGE_SIZE if neither are set. These are all different
> but valid definitions of "preferred blocksize for efficient IO".
> If you want to know the real block size of the filesystem, use
Definitely, thanks a lot!!