On Mon, Oct 12, 2015 at 08:34:36PM -0600, Andreas Dilger wrote: > The commit comment says enable meta_bg if 1/2 of the block group > is full, but the code checks for 3/4 of the block group is full. Which one > Should it be? Oops. It should be 3/4 since it's generally advantageous to leave meta_bg off as long as possible so as to keep the group descriptors nearby. That said, I also toyed with the idea of making the switch if total overhead (gdt + inodes) uses more than 3/4 of a BG. But the inode size/ratio is configurable, so I went with just checking gdt for now. --D > > Cheers, Andreas > > > On Oct 12, 2015, at 15:56, Darrick J. Wong <darrick.wong@xxxxxxxxxx> wrote: > > > > If during formatting we'd lose more than half of a block group to > > group descriptors and other metadata, enable the meta_bg feature. > > This enables us to create >500T filesystems with default options. > > > > Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx> > > --- > > lib/ext2fs/initialize.c | 5 +++++ > > 1 file changed, 5 insertions(+) > > > > > > diff --git a/lib/ext2fs/initialize.c b/lib/ext2fs/initialize.c > > index f672a27..b5ca928 100644 > > --- a/lib/ext2fs/initialize.c > > +++ b/lib/ext2fs/initialize.c > > @@ -381,6 +381,11 @@ ipg_retry: > > overhead = (int) (3 + fs->inode_blocks_per_group + > > super->s_reserved_gdt_blocks); > > > > + /* Enable meta_bg if we'd lose more than 3/4 of a BG to GDT blocks. */ > > + if (super->s_reserved_gdt_blocks + fs->desc_blocks > > > + super->s_blocks_per_group * 3 / 4) > > + fs->super->s_feature_incompat |= EXT2_FEATURE_INCOMPAT_META_BG; > > + > > if (fs->super->s_feature_incompat & EXT2_FEATURE_INCOMPAT_META_BG) > > overhead++; > > else > > > > -- > > 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 -- 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
