On Mon, Jul 07, 2014 at 05:13:49PM -0400, Benjamin LaHaise wrote:s > Hi folks, > > I've just ran into a bug with the ext4 codebase in 3.4.91 that doesn't seem > to exist in ext3, and was wondering if anyone has encountered this before. > I have a 7.4TB ext3 filesystem that has been filled with 1.8TB of data. > When this filesystem is freshly mounted, the first write to the filesystem > takes a whopping 96 seconds to complete, during which time the system is > reading about 1000 blocks per second. Subsequent writes are much quicker. > The problem seems to be that ext4 is loading all of the bitmaps on the > filesystem before the first write proceeds. The backtrace looks roughly as > follows: So the issue is that ext3 will just allocate the first free block it can find, even if it is a single free block in block group #1001, followed by a single free block in block group #2002. Ext4 tries a harder to find contiguous blocks. If you are using an ext3 file system format, the block allocation bitmaps are scattered across the entire file system, so we end up doing a lot random 4k seeks. We can try to be a bit smarter about how we try to search the file system for free blocks. Out of curiosity, can you send me a copy of the contents of: /proc/fs/ext4/dm-XX/mb_groups Thanks!! - 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
