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 blks >>>> = 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 > 64k. 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 machine. :( > > 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 > statfs(2). Definitely, thanks a lot!! -Jeff > > Cheers, > > Dave. _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
