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 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
