On Dec 7, 2011, Christian Brunner <c...@muc.de> wrote: > With this patch applied I get much higher write-io values than without > it. Some of the other patches help to reduce the effect, but it's > still significant.
> iostat on an unpatched node is giving me: > Device: rrqm/s wrqm/s r/s w/s rsec/s wsec/s > avgrq-sz avgqu-sz await svctm %util > sda 105.90 0.37 15.42 14.48 2657.33 560.13 > 107.61 1.89 62.75 6.26 18.71 > while on a node with this patch it's > sda 128.20 0.97 11.10 57.15 3376.80 552.80 > 57.58 20.58 296.33 4.16 28.36 > Also interesting, is the fact that the average request size on the > patched node is much smaller. That's probably expected for writes, as bitmaps are expected to be more fragmented, even if used only for metadata (or are you on SSD?) Bitmaps are just a different in-memory (and on-disk-cache, if enabled) representation of free space, that can be far more compact: one bit per disk block, rather than an extent list entry. They're interchangeable otherwise, it's just that searching bitmaps for a free block (bit) is somewhat more expensive than taking the next entry from a list, but you don't want to use up too much memory with long lists of e.g. single-block free extents. -- Alexandre Oliva, freedom fighter http://FSFLA.org/~lxoliva/ You must be the change you wish to see in the world. -- Gandhi Be Free! -- http://FSFLA.org/ FSF Latin America board member Free Software Evangelist Red Hat Brazil Compiler Engineer -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
