Re: Best OS & Configuration for Dual Xeon w/4GB &

Scott Marlowe wrote:
> On Mon, 2006-03-20 at 08:45, Jim C. Nasby wrote:
>
>>On Fri, Mar 17, 2006 at 05:00:34PM -0600, Scott Marlowe wrote:
>>
>>>>last pid: 5788; load averages: 0.32, 0.31, 0.28 up 127+15:16:08 13:59:24
>>>>169 processes: 1 running, 168 sleeping
>>>>CPU states: 5.4% user, 0.0% nice, 9.9% system, 0.0% interrupt, 84.7% idle
>>>>Mem: 181M Active, 2632M Inact, 329M Wired, 179M Cache, 199M Buf, 81M Free
>>>>Swap: 4096M Total, 216K Used, 4096M Free
>>>>
>>>> PID USERNAME PRI NICE SIZE RES STATE C TIME WCPU CPU COMMAND
>>>>14501 pgsql 2 0 254M 242M select 2 76:26 1.95% 1.95% postgre
>>>> 5720 root 28 0 2164K 1360K CPU0 0 0:00 1.84% 0.88% top
>>>> 5785 pgsql 2 0 255M 29296K sbwait 0 0:00 3.00% 0.15% postgre
>>>> 5782 pgsql 2 0 255M 11900K sbwait 0 0:00 3.00% 0.15% postgre
>>>> 5772 pgsql 2 0 255M 11708K sbwait 2 0:00 1.54% 0.15% postgre
>>>
>>>That doesn't look good. Is this machine freshly rebooted, or has it
>>>been running postgres for a while? 179M cache and 199M buffer with 2.6
>>>gig inactive is horrible for a machine running a 10gig databases.
>>
>>No, this is perfectly fine. Inactive memory in FreeBSD isn't the same as
>>Free. It's the same as 'active' memory except that it's pages that
>>haven't been accessed in X amount of time (between 100 and 200 ms, I
>>think). When free memory starts getting low, FBSD will start moving
>>pages from the inactive queue to the free queue (possibly resulting in
>>writes to disk along the way).
>>
>>IIRC, Cache is the directory cache, and Buf is disk buffers, which is
>>somewhat akin to shared_buffers in PostgreSQL.
>
>
> So, then, the inact is pretty much the same as kernel buffers in linux?
>

I think Freebsd 'Inactive' corresponds pretty closely to Linux's
'Inactive Dirty'|'Inactive Laundered'|'Inactive Free'.

From what I can see, 'Buf' is a bit misleading e.g. read a 1G file
randomly and you increase 'Inactive' by about 1G - 'Buf' might get to
200M. However read the file again and you'll see zero i/o in vmstat or
gstat. From reading the Freebsd architecture docs, I think 'Buf'
consists of those pages from 'Inactive' or 'Active' that were last kvm
mapped for read/write operations. However 'Buf' is restricted to a
fairly small size (various sysctls), so really only provides a lower
bound on the file buffer cache activity.

Sorry to not really answer your question Scott - how are Linux kernel
buffers actually defined?

Cheers

Mark