On 2011-03-21, at 8:05 PM, Arnd Bergmann wrote: > On Monday 21 March 2011 19:03:09 Andreas Dilger wrote: >> Note that mballoc was specifically designed to handle allocation >> requests that are aligned on RAID stripe boundaries, so it should >> be able to handle this for MMC as well. What is needed is to tell >> the filesystem what the underlying alignment is. That can be done >> at format time with mke2fs or afterward with tune2fs by using the >> "-E stripe_width" option. > > Ah, that sounds useful. So would I set the stripe_width to the > erase block size, and the block group size to a multiple of that? When you write "block group size" do you mean the ext4 block group? Then yes it would help. You could also consider setting the flex_bg size to a multiple of this, so that the bitmap blocks are grouped as a multiple of this size. However, they may not be aligned correctly, which needs extra effort that isn't obvious. I think it would be nice to have mke2fs take the stripe_width and/or flex_bg factor into account when sizing/aligning the bitmaps, but it doesn't yet. > Does this also work in (rare) cases where the erase block size is > not a power of two? It does (or is supposed to), but that isn't code that is exercised very much (most installations use a power-of-two size). Cheers, Andreas -- 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
