Re: abysmal performance

[Daniel J Blueman <daniel.blueman@gmail.com>]

On 3 May 2011 20:52, Chris Mason <chris.mason@oracle.com> wrote:
> Excerpts from Bernhard Schmidt's message of 2011-05-03 07:43:04 -0400=
:
>> Hi,
>>
>> > Using compression is not a problem, but in order to reduce the max=
imum
>> > amount of ram we need to uncompress an extent, we enforce a max si=
ze on
>> > the extent. =A0So you'll tend to have more extents, but they shoul=
d be
>> > close together on disk.
>> >
>> > Could you please do a filefrag -v on the file? =A0Lets see how bad=
 it
>> > really is.
>>
>>
>> root@schleppi:~# filefrag -v
>> /usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.4/cc1
>> Filesystem type is: 9123683e
>> File size of /usr/lib/x86_64-linux-gnu/gcc/x86_64-linux-gnu/4.4/cc1 =
is
>> 9361528 (2286 blocks, blocksize 4096)
>> =A0ext logical physical expected length flags
>> =A0 =A00 =A0 =A0 =A0 0 =A04542111 =A0 =A0 =A0 =A0 =A0 =A0 =A032
>> =A0 =A01 =A0 =A0 =A032 =A04542134 =A04542142 =A0 =A0 32
>> =A0 =A02 =A0 =A0 =A064 =A04573263 =A04542165 =A0 =A0 32
>
> Ok, looks like we could be doing a little better job when compression=
 is
> on to build out a bigger extent. =A0This shouldn't be causing trouble=
 on
> an ssd at all but on your rotating disk it'll be slightly slower.

It does seem the case generally; on 2.6.39-rc5, writing to a fresh
filesystem using rsync with BTRFS compression enabled, 128KB extents
seem very common [1] (filefrag inconsistency noted).

Defragmenting with compression gives a nice linear extent [2]. It
looks like it'll be a good win to prevent extents being split at
writeout for the read case on rotational media.

Daniel

--- [1]

# filefrag sdhci.ppm
sdhci.ppm: 173 extents found

# filefrag -v sdhci.ppm
=46ilesystem type is: 9123683e
=46ile size of sdhci.ppm is 36838232 (8994 blocks, blocksize 4096)
 ext logical physical expected length flags
   0       0  7410681              32
   1      32  7564365  7410712     32
   2      64  7875283  7564396     32
   3      96  8197111  7875314     32
   4     128  8459255  8197142     32
   5     160 10072355  8459286     32
   6     192 10556407 10072386     32
   7     224 11088956 10556438     32
   8     256  9435820 11088987     32
   9     288  9769977  9435851     32
  10     320 10032121  9770008     32
  11     352 11342839 10032152     32
  12     384 12129270 11342870     32
  13     416 12653556 12129301     32
  14     448 12915698 12653587     32
  15     480 12915705 12915729     32
  16     512 13439988 12915736     32
  17     544 13702133 13440019     32
  18     576 14163816 13702164     32
  19     608 14163823 14163847     32
  20     640 14163830 14163854     32
  21     672 14163837 14163861     32
  22     704 14163843 14163868     32
  23     736 14163849 14163874     32
  24     768 14163859 14163880     32
  25     800 14163869 14163890     32
  26     832 14163879 14163900     32
  27     864 14163889 14163910     32
  28     896 14163899 14163920     32
  29     928 14163909 14163930     32
  30     960 14163919 14163940     32
  31     992 14163929 14163950     32
  32    1024 14163939 14163960     32
  33    1056 14163949 14163970     32
  34    1088 14163958 14163980     32
  35    1120 14163967 14163989     32
  36    1152 14163976 14163998     32
  37    1184 14163985 14164007     32
  38    1216 14163994 14164016     32
  39    1248 14164003 14164025     32
  40    1280 14164012 14164034     32
  41    1312 14164021 14164043     32
  42    1344 14164031 14164052     32
  43    1376 14164041 14164062     32
  44    1408 14164050 14164072     32
  45    1440 14164060 14164081     32
  46    1472 14164070 14164091     32
  47    1504 14164080 14164101     32
  48    1536 14164090 14164111     32
  49    1568 14164100 14164121     32
  50    1600 14164109 14164131     32
  51    1632 14164119 14164140     32
  52    1664 14164129 14164150     32
  53    1696 14164139 14164160     32
  54    1728 14164148 14164170     32
  55    1760 14164157 14164179     32
  56    1792 14164166 14164188     32
  57    1824 14164176 14164197     32
  58    1856 14164186 14164207     32
  59    1888 14164196 14164217     32
  60    1920 14164205 14164227     32
  61    1952 14164214 14164236     32
  62    1984 14164223 14164245     32
  63    2016 14164233 14164254     32
  64    2048 14164243 14164264     32
  65    2080 14164252 14164274     32
  66    2112 14164262 14164283     32
  67    2144 14164272 14164293     32
  68    2176 14164282 14164303     32
  69    2208 14164292 14164313     32
  70    2240 14164302 14164323     32
  71    2272 14164311 14164333     32
  72    2304 14164321 14164342     32
  73    2336 14164331 14164352     32
  74    2368 14164340 14164362     32
  75    2400 14164350 14164371     32
  76    2432 14164360 14164381     32
  77    2464 14164369 14164391     32
  78    2496 14164379 14164400     32
  79    2528 14164389 14164410     32
  80    2560 14164398 14164420     32
  81    2592 14164407 14164429     32
  82    2624 14164416 14164438     32
  83    2656 14164425 14164447     32
  84    2688 14164434 14164456     32
  85    2720 14164443 14164465     32
  86    2752 14164452 14164474     32
  87    2784 14164462 14164483     32
  88    2816 14164472 14164493     32
  89    2848 14164481 14164503     32
  90    2880 14164490 14164512     32
  91    2912 14164499 14164521     32
  92    2944 14164508 14164530     32
  93    2976 14164517 14164539     32
  94    3008 14164526 14164548     32
  95    3040 14164535 14164557     32
  96    3072 14164545 14164566     32
  97    3104 14164554 14164576     32
  98    3136 14164563 14164585     32
  99    3168 14164573 14164594     32
 100    3200 14164582 14164604     32
 101    3232 14164591 14164613     32
 102    3264 14164600 14164622     32
 103    3296 14164609 14164631     32
 104    3328 14164618 14164640     32
 105    3360 14164628 14164649     32
 106    3392 14164637 14164659     32
 107    3424 14164646 14164668     32
 108    3456 14164656 14164677     32
 109    3488 14164665 14164687     32
 110    3520 14164674 14164696     32
 111    3552 14164684 14164705     32
 112    3584 14164693 14164715     32
 113    3616 14164702 14164724     32
 114    3648 14164711 14164733     32
 115    3680 14164720 14164742     32
 116    3712 14164729 14164751     32
 117    3744 14164739 14164760     32
 118    3776 14164748 14164770     32
 119    3808 14164757 14164779     32
 120    3840 14164766 14164788     32
 121    3872 14164775 14164797     32
 122    3904 14164784 14164806     32
 123    3936 14164793 14164815     32
 124    3968 14164802 14164824     32
 125    4000 14164811 14164833     32
 126    4032 14164820 14164842     32
 127    4064 14164829 14164851     32
 128    4096 14164838 14164860     32
 129    4128 14164848 14164869     32
 130    4160 14164857 14164879     32
 131    4192 14164866 14164888     32
 132    4224 14164876 14164897     32
 133    4256 14164885 14164907     32
 134    4288 14164895 14164916     32
 135    4320 14164905 14164926     32
 136    4352 14164915 14164936     32
 137    4384 14164925 14164946     32
 138    4416 14164935 14164956     32
 139    4448 14164945 14164966     32
 140    4480 14164955 14164976     32
 141    4512 14164965 14164986     32
 142    4544 14164975 14164996     32
 143    4576 14164986 14165006     32
 144    4608 14164997 14165017     32
 145    4640 14165007 14165028     32
 146    4672 14165018 14165038     32
 147    4704 14165029 14165049     32
 148    4736 14165039 14165060     32
 149    4768 14165049 14165070    224
 150    4992 14165273              32
 151    5024 14165283 14165304     32
 152    5056 14165294 14165314     32
 153    5088 14165305 14165325     32
 154    5120 14165315 14165336     32
 155    5152 14165326 14165346     32
 156    5184 14165337 14165357     32
 157    5216 14165347 14165368     32
 158    5248 14165358 14165378     32
 159    5280 14165369 14165389    224
 160    5504 14165593              32
 161    5536 14165603 14165624     32
 162    5568 14165613 14165634     32
 163    5600 14165623 14165644     32
 164    5632 14165633 14165654     32
 165    5664 14165643 14165664     32
 166    5696 14165653 14165674     32
 167    5728 14165663 14165684    288
 168    6016 14165951              32
 169    6048 14165960 14165982     32
 170    6080 14165969 14165991     32
 171    6112 14165978 14166000     32
 172    6144 14165988 14166009   2850 eof
sdhci.ppm: 170 extents found

--- [2]

# btrfs filesystem defragment -c sdhci.ppm

# filefrag -v sdhci.ppm
=46ilesystem type is: 9123683e
=46ile size of sdhci.ppm is 36838232 (8994 blocks, blocksize 4096)
 ext logical physical expected length flags
   0       0 233041476            8994 eof
sdhci.ppm: 1 extent found
--=20
Daniel J Blueman
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