On Mon, Apr 20, 2015 at 10:26:45PM -0400, Theodore Ts'o wrote: > 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. Eh, you're right, let's drop this one. Honestly it's been so long I don't remember my motivation for writing this up in the first place. Thanks for pulling in the e2fsck readahead pieces, though! --D > > - 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 -- 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
