4.8 ffs_dirpref problem

[Ken Marx]

Don Lewis wrote:
> On 30 Oct, Ken Marx wrote:
> 
>>
>>Don Lewis wrote:
> 
> [snip]
> 
>>>You might try the lightly tested patch below.  It tweaks the dirpref
>>>algorithm so that cylinder groups with free space >= 75% of the average
>>>free space and free inodes >= 75% of the average number of free inodes
>>>are candidates for allocating the directory.  It will not chose a
>>>cylinder group that does not have at least one free block and one free
>>>inode.
>>>
>>>It also decreases maxcontigdirs as the free space decreases so that a
>>>cluster of directories is less likely to cause the cylinder group to
>>>overflow.  I think it would be better to tune maxcontigdirs individually
>>>for each cylinder group, based on the free space in that cylinder group,
>>>but that is more complex ...
> 
> [snip]
> 
>>Anyway - I just tested your patch. Again, unloaded system, repeatedly
>>untaring a 1.5gb file, starting at 97% capacity. and:
>>	
>>	tunefs: average file size: (-f)                            49152
>>	tunefs: average number of files in a directory: (-s)       1500
>>	...
>>
>>Takes about 74 system secs per 1.5gb untar:
>>-------------------------------------------
>>/dev/da0s1e 558889580 497843972 16334442    97% 6858407 63316311   10%   /raid
>>      119.23 real         1.28 user        73.09 sys
>>/dev/da0s1e 558889580 499371100 14807314    97% 6879445 63295273   10%   /raid
>>      111.69 real         1.32 user        73.65 sys
>>/dev/da0s1e 558889580 500898228 13280186    97% 6900483 63274235   10%   /raid
>>      116.67 real         1.44 user        74.19 sys
>>/dev/da0s1e 558889580 502425356 11753058    98% 6921521 63253197   10%   /raid
>>      114.73 real         1.25 user        75.01 sys
>>/dev/da0s1e 558889580 503952484 10225930    98% 6942559 63232159   10%   /raid
>>      116.95 real         1.30 user        74.10 sys
>>/dev/da0s1e 558889580 505479614 8698800    98% 6963597 63211121   10%   /raid
>>      115.29 real         1.39 user        74.25 sys
>>/dev/da0s1e 558889580 507006742 7171672    99% 6984635 63190083   10%   /raid
>>      114.01 real         1.16 user        74.04 sys
>>/dev/da0s1e 558889580 508533870 5644544    99% 7005673 63169045   10%   /raid
>>      119.95 real         1.32 user        75.05 sys
>>/dev/da0s1e 558889580 510060998 4117416    99% 7026711 63148007   10%   /raid
>>      114.89 real         1.33 user        74.66 sys
>>/dev/da0s1e 558889580 511588126 2590288    99% 7047749 63126969   10%   /raid
>>      114.91 real         1.58 user        74.64 sys
>>/dev/da0s1e 558889580 513115254 1063160   100% 7068787 63105931   10%   /raid
>>tot:     1161.06 real        13.45 user       742.89 sys
>>
>>Compares pretty favorably to our naive, retro 4.4 dirpref hack
>>that averages in the mid-high 60's:
>>--------------------------------------------------------------------
>>/dev/da0s1e 558889580 497843952 16334462    97% 6858406 63316312   10%   /raid
>>      110.19 real         1.42 user        65.54 sys
>>/dev/da0s1e 558889580 499371080 14807334    97% 6879444 63295274   10%   /raid
>>      105.47 real         1.47 user        65.09 sys
>>/dev/da0s1e 558889580 500898208 13280206    97% 6900482 63274236   10%   /raid
>>      110.17 real         1.48 user        64.98 sys
>>/dev/da0s1e 558889580 502425336 11753078    98% 6921520 63253198   10%   /raid
>>      131.88 real         1.49 user        71.20 sys
>>/dev/da0s1e 558889580 503952464 10225950    98% 6942558 63232160   10%   /raid
>>      111.61 real         1.62 user        67.47 sys
>>/dev/da0s1e 558889580 505479594 8698820    98% 6963596 63211122   10%   /raid
>>      131.36 real         1.67 user        90.79 sys
>>/dev/da0s1e 558889580 507006722 7171692    99% 6984634 63190084   10%   /raid
>>      115.34 real         1.49 user        65.61 sys
>>/dev/da0s1e 558889580 508533850 5644564    99% 7005672 63169046   10%   /raid
>>      110.26 real         1.39 user        65.26 sys
>>/dev/da0s1e 558889580 510060978 4117436    99% 7026710 63148008   10%   /raid
>>      116.15 real         1.51 user        65.47 sys
>>/dev/da0s1e 558889580 511588106 2590308    99% 7047748 63126970   10%   /raid
>>      112.74 real         1.37 user        65.01 sys
>>/dev/da0s1e 558889580 513115234 1063180   100% 7068786 63105932   10%   /raid
>>     1158.36 real        15.01 user       686.57 sys
>>
>>Without either, we'd expect timings of 5-20 minutes when things are
>>going poorly.
>>
>>Happy to test further if you have tweaks to your patch or
>>things you'd like us to test in particular. E.g., load,
>>newfs, etc.
> 
> 
> You might want to try your hash patch along my patch to see if
> decreasing the maximum hash chain lengths makes a difference in system
> time.
> 
> 

Sorry - should hvae mentioned: Both tests included our hash patch.
I just re-ran with the hash stuff back to original. Sorry to say
there's no appreciable difference. Using your dirpref patch, still
apprx 75 sys sec/1.5gb:

	tot:      1185.54 real        14.15 user       747.43 sys

Prehaps the dirpref patch lowers the frequency of having to search so much,
and hence exercises the hashtable less.

Or I'm doing something lame.

k

-- 
Ken Marx, kmarx at vicor-nb.com
We have to move. We must not stand pat and achieve closure on customer's 
customer.
		- http://www.bigshed.com/cgi-bin/speak.cgi