On Wed, Apr 01, 2015 at 07:34:33PM -0700, Darrick J. Wong wrote: > Use a bitmap to track which directories we want to rehash, since > bitmaps will use less memory. This enables us to clean up the > rehash-all case to use inode_dir_map, and we can free the dirinfo > memory sooner. > > Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx> Um, how is it that bitmaps will use less memory? Directories generally don't use contiguous inode numbers (i.e., it's not that often that inodes N-1. N, and N+1 will all be directoriess), and and the rbtree data structure is going to have more pointer overhead compared with the u32 list. In the case of the bitarray representation, the memory usage is nr_inodes / 8 in bytes. The memory usage of the u32 list is (nr_dirs * 4) bytes. Given that the number of inodes is generally something that we've massively provisioned, that's not all that likely. Looking at some files systems I have handy, it's no contest: Filesystem nr_inodes / 8 nr_dirs * 4 /dev/sda3 1,176,576 382,424 /dev/heap/u1 655,360 63,384 Using inode_dir_map for the rehash-all case is a good idea, but I'm not sure it follows that we should ues a bitmap for the non-rehash-all case. - Ted -- 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
