Re: Question on block group allocation

[Curt Wohlgemuth <curtw@google.com>]

[-- Attachment #1: Type: text/plain, Size: 1750 bytes --]

Hi Ted:

On Mon, Apr 27, 2009 at 3:40 PM, Theodore Tso <tytso@mit.edu> wrote:
> On Sun, Apr 26, 2009 at 11:29:39PM -0600, Curt Wohlgemuth wrote:
>> The random read throughput on the 10GB file went from ~16 MB/s to ~22
>> MB/s after Andreas' patch; the total fragmentation of the file was
>> much lower than before his patch.
>>
>> However, the number of extents went up by quite a bit (I don't have
>> the debugfs output in front of me at the moment, sorry).
>
> I'm curious what you meant by the combination of these two statements,
> "the total fragmentation of the file was much lower than before his
> patch", and "the number of extents went up by quite a bit".  Can you
> send me the debugfs output when you have a chance?

Sorry it's been so long for me to reply.

Okay, my phrasing was not as precise as it could have been.  What I
meant by "total fragmentation" was simply that the range of physical
blocks for the 10GB file was much lower with Andreas' patch:

Before patch:  8282112 - 103266303
After patch: 271360 - 5074943

The number of extents is much larger.  See the attached debugfs output.

Here's the output of "e2fsck -E fragcheck" on the block devices;
remember, though, that each one has only 3 files:

-rw-rw-r--    1 root     root     10737418240 Apr 23 15:33 10g
-rw-rw-r--    1 root     root     4294967296 Apr 23 15:30 4g
-rw-rw-r--    1 root     root     4294967296 Apr 23 15:30 4g-2
drwx------    2 root     root        16384 Apr 23 15:27 lost+found/

Before patch:
e2fsck 1.41.3 (12-Oct-2008)
/dev/hdm3: clean, 14/45760512 files, 7608255/183010471 blocks

After patch:
e2fsck 1.41.3 (12-Oct-2008)
/dev/hdo3: clean, 14/45760512 files, 7608258/183010471 blocks


Thanks,
Curt

[-- Attachment #2: debugfs.before-patch --]
[-- Type: application/octet-stream, Size: 888 bytes --]

Inode: 14   Type: regular    Mode:  0664   Flags: 0x80000
Generation: 3039487964    Version: 0x00000000:00000001
User:     0   Group:     0   Size: 10737418240
File ACL: 0    Directory ACL: 0
Links: 1   Blockcount: 20971528
Fragment:  Address: 0    Number: 0    Size: 0
 ctime: 0x49efa0f4:b4e10eb4 -- Wed Apr 22 15:57:56 2009
 atime: 0x49f89bb5:2f6e87cc -- Wed Apr 29 11:25:57 2009
 mtime: 0x49efa0f4:b4e10eb4 -- Wed Apr 22 15:57:56 2009
crtime: 0x49efa0d1:449576d0 -- Wed Apr 22 15:57:21 2009
Size of extra inode fields: 28
BLOCKS:
(IND):8396832, (0-106495):8282112-8388607, (106496-399359):11241472-11534335, (399360-888831):20482048-20971519, (888832-1116159):23889920-24117247, (1116160-1277951):71665664-71827455, (1277952-1767423):78678016-79167487, (1767424-2125823):102402048-102760447, (2125824-2148351):102768672-102791199, (2148352-2621439):102793216-103266303
TOTAL: 2621441


[-- Attachment #3: debugfs.after-patch --]
[-- Type: application/octet-stream, Size: 12951 bytes --]

Inode: 14   Type: regular    Mode:  0664   Flags: 0x80000
Generation: 310363953    Version: 0x00000000:00000001
User:     0   Group:     0   Size: 10737418240
File ACL: 0    Directory ACL: 0
Links: 1   Blockcount: 20971536
Fragment:  Address: 0    Number: 0    Size: 0
 ctime: 0x49f0ec9f:2956e76c -- Thu Apr 23 15:33:03 2009
 atime: 0x49f0ec2b:588bc38c -- Thu Apr 23 15:31:07 2009
 mtime: 0x49f0ec9f:2956e76c -- Thu Apr 23 15:33:03 2009
crtime: 0x49f0ec2b:588bc38c -- Thu Apr 23 15:31:07 2009
Size of extra inode fields: 28
BLOCKS:
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(315392-317439):1835008-1837055, (317440-319487):1841152-1843199, (319488-321535):1847296-1849343, (321536-323583):1853440-1855487, (323584-325631):1859584-1861631, (325632-327679):1865728-1867775, (327680-329727):1871872-1873919, (329728-331775):1878016-1880063, (331776-333823):1884160-1886207, (333824-335871):1890304-1892351, (335872-337919):1896448-1898495, (337920-339967):1902592-1904639, (339968-342015):1908736-1910783, (342016-344063):1914880-1916927, (344064-346111):1921024-1923071, (346112-348159):1927168-1929215, (348160-350207):1933312-1935359, (350208-352255):1939456-1941503, (352256-354303):1945600-1947647, (354304-356351):1951744-1953791, (356352-358399):1957888-1959935, (358400-360447):1964032-1966079, (360448-362495):1970176-1972223, (362496-364543):1976320-1978367, (364544-366591):1982464-1984511, (366592-368639):1988608-1990655, (368640-370687):1994752-1996799, (370688-372735):2000896-2002943, (372736-374783):2007040-2009087, (374784-376831):2013184-2015231, 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(638976-641023):2811904-2813951, (641024-643071):2816000-2818047, (643072-645119):2820096-2822143, (645120-647167):2824192-2826239, (647168-649215):2828288-2830335, (649216-651263):2832384-2834431, (651264-653311):2836480-2838527, (653312-655359):2840576-2842623, (655360-657407):2844672-2846719, (657408-659455):2848768-2850815, (659456-661503):2852864-2854911, (661504-663551):2856960-2859007, (663552-665599):2861056-2863103, (665600-667647):2865152-2867199, (667648-669695):2869248-2871295, (669696-671743):2873344-2875391, (671744-673791):2877440-2879487, (673792-675839):2881536-2883583, (675840-677887):2885632-2887679, (677888-679935):2889728-2891775, (679936-681983):2893824-2895871, (681984-684031):2897920-2899967, (684032-686079):2902016-2904063, (686080-688127):2906112-2908159, (688128-690175):2910208-2912255, (690176-692223):2914304-2916351, (692224-694271):2918400-2920447, (694272-696319):2922496-2924543, (696320-698367):2926592-2928639, (698368-700415):2930688-2932735, 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(763904-765951):3063808-3065855, (765952-767999):3067904-3069951, (768000-770047):3072000-3074047, (770048-772095):3076096-3078143, (772096-774143):3080192-3082239, (774144-776191):3084288-3086335, (776192-778239):3088384-3090431, (778240-780287):3092480-3094527, (780288-782335):3096576-3098623, (782336-784383):3100672-3102719, (784384-825343):3104768-3145727, (825344-1316863):3178496-3670015, (1316864-1710079):3702784-4095999, (1710080-1806335):4098048-4194303, (1806336-2297855):4227072-4718591, (2297856-2621439):4751360-5074943
TOTAL: 2621442