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SubjectAdaptive Readahead V14 - statistics question...
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Running 2.6.17-rc4-mm3 + V14.  I see this in /debug/readahead/events:

[table summary] total initial state context contexta backward onthrash onseek none
random_rate 8% 0% 4% 46% 9% 44% 0% 38% 18%
ra_hit_rate 89% 97% 90% 40% 83% 76% 0% 49% 0%
la_hit_rate 62% 99% 88% 29% 84% 9500% 0% 200% 3700%
var_ra_size 703 4 8064 39 5780 3 0 59 3010
avg_ra_size 6 2 67 6 33 2 0 4 36
avg_la_size 37 1 96 4 45 0 0 0 0

Are the 9500%, 200%, and 3700% numbers in la_hit_rate related to reality
in any way, or is something b0rken?

And is there any documentation on what these mean, so you can tell if it's
doing anything useful? (One thing I've noticed is that xmms, rather than gobble
up 100K of data off disk every 10 seconds or so, snarfs a big 2M chunk every
3-4 minutes, often sucking in an entire song at (nearly) one shot...)

(Complete contents of readahead/events follows, in case it helps diagnose...)

[table requests] total initial state context contexta backward onthrash onseek none
cache_miss 3934 543 93 2013 39 1199 0 47 417
random_read 1772 59 49 1059 11 575 0 19 327
io_congestion 4 0 4 0 0 0 0 0 0
io_cache_hit 1082 1 63 855 14 144 0 5 0
io_block 26320 18973 3519 2225 265 1288 0 50 1371
readahead 18601 15540 1008 1203 110 710 0 30 1483
lookahead 1972 153 671 1050 98 0 0 0 0
lookahead_hit 1241 152 596 312 84 95 0 2 37
lookahead_ignore 0 0 0 0 0 0 0 0 0
readahead_mmap 0 0 0 0 0 0 0 0 0
readahead_eof 14951 14348 569 19 15 0 0 0 0
readahead_shrink 0 0 0 0 0 0 0 0 70
readahead_thrash 0 0 0 0 0 0 0 0 0
readahead_mutilt 0 0 0 0 0 0 0 0 0
readahead_rescue 0 0 0 0 0 0 0 0 138

[table pages] total initial state context contexta backward onthrash onseek none
cache_miss 6541 2472 754 2026 43 1199 0 47 1194
random_read 1784 62 51 1065 12 575 0 19 337
io_congestion 396 0 396 0 0 0 0 0 0
io_cache_hit 10185 2 571 7930 1383 293 0 6 0
readahead 111015 30757 67949 6864 3642 1681 0 122 53677
readahead_hit 98812 30052 61602 2762 3041 1294 0 61 277
lookahead 72607 185 64222 3734 4466 0 0 0 0
lookahead_hit 68640 184 59207 4475 4774 0 0 0 0
lookahead_ignore 0 0 0 0 0 0 0 0 0
readahead_mmap 0 0 0 0 0 0 0 0 0
readahead_eof 39959 25045 14102 64 748 0 0 0 0
readahead_shrink 0 0 0 0 0 0 0 0 1076
readahead_thrash 0 0 0 0 0 0 0 0 0
readahead_mutilt 0 0 0 0 0 0 0 0 0
readahead_rescue 0 0 0 0 0 0 0 0 9538

[table summary] total initial state context contexta backward onthrash onseek none
random_rate 8% 0% 4% 46% 9% 44% 0% 38% 18%
ra_hit_rate 89% 97% 90% 40% 83% 76% 0% 49% 0%
la_hit_rate 62% 99% 88% 29% 84% 9500% 0% 200% 3700%
var_ra_size 703 4 8064 39 5780 3 0 59 3010
avg_ra_size 6 2 67 6 33 2 0 4 36
avg_la_size 37 1 96 4 45 0 0 0 0

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