Re: [or-talk] Re: huge pages, was where are the exit nodes gone?

[Scott Bennett <bennett@xxxxxxxxxx>]

     On Tue, 13 Apr 2010 18:18:02 -0700 (PDT) Christian Kujau
<lists@xxxxxxxxxxxxxxx> wrote:
>On Tue, 13 Apr 2010 at 05:58, Scott Bennett wrote:
>> and straighten us out.  Remember that Olaf runs the highest-load-bearing
>> tor node in our whole network, and there are at least two or four dozen
>> others that should be considered heavyweight relays that are also on LINUX
>> systems.
>
>...and some of them are running on old notebooks and the tor process is 
>only a few megabytes in size :-|

     If tor is only using, say, 25 MB or so, then tor's CPU load is probably
low anyway.  Nevertheless, any other process on a small x86-type of LINUX
system that has a working set greater than 256 KB of instruction pages and/or
256 KB of data+stack pages would benefit from using enough hugepages to cover
its needs.
>
>However, if it turns out that using hugepages in Linux would help larger 
>Tor installations (and "superpages" can be recommended for *BSD systems[0]
>as well), maybe this can be documented somehwere under doc/ or in the 
>wiki. But let's see how Olaf's experiment turns out.
>
>Christian.
>
>[0] http://www.freebsd.org/releases/7.2R/relnotes-detailed.html
>    This is disabled by default and can be enabled by setting a loader 
>    tunable vm.pmap.pg_ps_enabled to 1.

     A couple of caveats regarding the automatic version available in
FreeBSD 7.2 and later releases are in order here.  To the best of my
knowledge, this feature is not yet available :-( in any of the other BSDs,
so tor relay operators on NetBSD, OpenBSD, DragonflyBSD, MirBSD, etc.
can disregard all of this stuff for the time being.  Another matter is
that FreeBSD systems on AMD processors of designs older than the K10 types
may actually get poorer performance with the feature enabled.  That's
because on those processors the number of entries in the TLBs is drastically
reduced in the 4 MB pages mode.  So on pre-K10 AMD processors the official
recommendation that I read was to try it if you have a large process that
is bogging down, and just see what happens.  If it helps, then that's great,
but be prepared for the strong possibility that it might just make matters
worse.


                                  Scott Bennett, Comm. ASMELG, CFIAG
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