On Wed, Jan 15, 2014 at 02:28:02PM -0500, Benjamin LaHaise wrote: > Hi folks, > > As a follow on to my previous issue with ext3, it's looking like the > indirect block allocator in ext4 is not doing a very good job of making > block allocations sequential. On a 1GB test filesystem, I'm getting > the following allocation results for 10MB files (written out with a single > 10MB write()): > > debugfs: stat testfile.0 > Inode: 12 Type: regular Mode: 0600 Flags: 0x0 Generation: 2584871807 > User: 0 Group: 0 Size: 10485760 > File ACL: 0 Directory ACL: 0 > Links: 1 Blockcount: 20512 > Fragment: Address: 0 Number: 0 Size: 0 > ctime: 0x52d6de73 -- Wed Jan 15 14:16:03 2014 > atime: 0x52d6de27 -- Wed Jan 15 14:14:47 2014 > mtime: 0x52d6de73 -- Wed Jan 15 14:16:03 2014 > BLOCKS: > (0-11):24576-24587, (IND):8797, (12-1035):24588-25611, (DIND):8798, (IND):8799, > (1036-2059):25612-26635, (IND):10248, (2060-2559):26636-27135 > TOTAL: 2564 A dumpe2fs would be nice, but I think I have enough here to speculate: The data blocks are all sequential, which looks like what one would expect from mballoc. Is your complaint is that the *IND blocks are not inline with the data blocks, like what ext3 did? FWIW, ext3 did something like this: (0-11):6144-6155, (IND):6156, (12-1035):6157-7180, (DIND):7181, (IND):7182, (1036-2059):7183-8206, (IND):8207, (2060-2559):8208-8707 I think the behavior that you're seeing is ext4 trying to keep the mapping blocks close to the inode table to avoid fragmenting the file -- see ext4_find_near() in indirect.c. There's an XXX comment in ext4_find_goal() that implies that someone might have wanted to tie in with mballoc, which I suppose you could use to restore the ext3 behavior... but there's no way to do that. --D > > debugfs: stat testfile.1 > Inode: 15 Type: regular Mode: 0600 Flags: 0x0 Generation: 1625569093 > User: 0 Group: 0 Size: 10485760 > File ACL: 0 Directory ACL: 0 > Links: 1 Blockcount: 20512 > Fragment: Address: 0 Number: 0 Size: 0 > ctime: 0x52d6df0f -- Wed Jan 15 14:18:39 2014 > atime: 0x52d6df0f -- Wed Jan 15 14:18:39 2014 > mtime: 0x52d6df0f -- Wed Jan 15 14:18:39 2014 > BLOCKS: > (0-11):12288-12299, (IND):8787, (12-1035):12300-13323, (DIND):8790, (IND):8791, > (1036-2059):13324-14347, (IND):8789, (2060-2559):14348-14847 > TOTAL: 2564 > > debugfs: > > To give folks an idea about how significant an impact on performance this > is, using ext4 to mount my ext3 filesystem and create files is resulting > in a 10-15% reduction in speed when data is being read back into memory. > I also tested 3.11.7 and see the same poor allocation layout. I also > tried turning off delalloc, but there was no change in the layout of the > data blocks. Has anyone got any ideas what's going on here? Cheers, > > -ben > -- > "Thought is the essence of where you are now." > -- > 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
