On Dec 11, 2007 10:08 -0600, Jose R. Santos wrote: > > I'd think being able to avoid the divide for every inode allocation is more > > important than 8 bits in the superblock. > > We already avoid the divide since what we store in the sbi IS the bits > which are calculated at mount time for each fs. Base on the other > fields in the super block struct, I decided to put explicit size of the > flexbg in the super block. The kernel code can decide how best to use > that number which in this case its used to calculate the number of bits > in order to avoid doing divides. > > So this is really a styling issue in how to record data in the super > block. The only technical issue with this is whether it's important to > save those extra 8 bits in the super block struct. Well, if it is stored in the superblock as a non-power-of-two value, then there always exists the possibility that it is set incorrectly (maybe by a version of mke2fs that doesn't verify this) and the code will not do the right thing. Storing it in bits (as is done with e.g. s_log_block_size and s_log_frag_size) ensures there is no possibility of a value that isn't a power-of-two. Cheers, Andreas -- Andreas Dilger Sr. Staff Engineer, Lustre Group Sun Microsystems of Canada, Inc. - To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
