On 3 May 2011 20:52, Chris Mason <chris.ma...@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 maximum >> > amount of ram we need to uncompress an extent, we enforce a max size on >> > the extent. So you'll tend to have more extents, but they should be >> > close together on disk. >> > >> > Could you please do a filefrag -v on the file? Lets 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) >> ext logical physical expected length flags >> 0 0 4542111 32 >> 1 32 4542134 4542142 32 >> 2 64 4573263 4542165 32 > > Ok, looks like we could be doing a little better job when compression is > on to build out a bigger extent. This 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 Filesystem type is: 9123683e File 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 Filesystem type is: 9123683e File 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 -- Daniel J Blueman -- 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
