128 Bucket Failures?

[Ivan Voras]

Chris Pratt wrote:
> I have asked this before a couple of years ago but received no
> replies. I assumed that's because it's a somewhat obscure question.
> I'm still interested and thought I might try again in case someone
> new is watching this list who might know.
> 
> A vmstat -z on my highest traffic server always shows the failures
> as below on 128 Bucket. It also goes to having 0 free rather soon
> after the system is restarted and never returns to having more than
> 1 free in that column and yet always has the highest number of
> requests by far. Does this mean anything significant? Is it
> something I should tune or even can be tuned?

UMA buckets seem to be some kind of cache for SMP-optimized allocations
- I hope someone who knows it better will explain them.

> Here is the output of the vmstat -z with everything chopped out
> besides the 128 Bucket line. The machine it's on is an 8 core 8 GB
> Tyan and shouldn't really be starved for anything in my way of thinking.
> 
> vmstat -z
> ITEM                     SIZE     LIMIT      USED      FREE  REQUESTS  FAILURES
> 
> 128 Bucket:              1048,        0,     2043,        0,    13591,  6511069

What is the server used for?

Here's a snapshot from a very loaded apache+php+pgsql web server, uptime
60 days (since the last power outage):

16 Bucket:                 76,        0,       42,       58,      125,
      0
32 Bucket:                140,        0,       76,       64,      183,
      0
64 Bucket:                268,        0,       74,       38,      438,
     11
128 Bucket:               524,        0,     2060,      642,   788828,
   6985

A generic advice would be to increase vm.kmem_size (you're using AMD64,
right?) and see what happens.

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