[CentOS] Kernel update = slower ?

William L. Maltby BillsCentOS at triad.rr.com
Sun Jun 4 14:28:33 UTC 2006


On Sun, 2006-06-04 at 09:57 -0400, Sam Drinkard wrote:
> 
> William L. Maltby wrote:
> 
> >On Thu, 2006-06-01 at 19:18 -0400, Sam Drinkard wrote:
> >  
> >
> >>Johnny,
> >>
> >>    After reading about the VM issue, I concur. <snip>

> >I forget the start of this thread... was 64 bit only? Anyway, I had my
> >32bit lock a couple times with symptoms like Sam mentions. Lots of swap
> >used and no reason for it. Was using lots of open browsers, a couple
> >different GUI MUAs, etc.
> >
> >Turned off things I didn't need <snip>

> >A *biggie*, maybe, is the stupid readahead and readahead_early stuff.
> ><snip>

> >Up now for 6 days running similar load (I think, haven't bothered to
> >really measure it) and swap use is still good and response is still
> >good.
> ><snip>

> After uptime of a little over 3 days now, I'm not seeing any increase in 
> swap as I did prior, but then again, I don't exactly recall how long it 
> took before swap started increasing.

For my symptoms to appear, it took a combo of time up and an increase in
load. Don't know if this is coincidence or cause and effect.

> One thing I do notice is for some 
> reason, the applications that nomally would consume between 1.2 - 1.4G 
> of memory is now down to 1.1 - 1.2, and swap is only lightly touched at 
> 181mb.

Again, mine is only a workstation, so I don't know how this applies to
you. My max on the previous session was 64k into swap. That was about 4
days up, IIRC and I tried at several points to dupe the conditions
(opened several browsers, multiple users, several different
type/instances of MUAs, several ssh to my LAN server, etc.).

I've since turned sendmail back on so I can do some LAN-internal things
with it. Pretty much stock config except that I removed the restriction
on localhost (a DAEMON_OPTION in the sendmail.mc file). Needed to reboot
to to test LVM config changes (new stuff for me) and after a day and a
half of running, 0k in swap with medium load.

> Don't know if this is due to the kernal update or what, but it 
> would seem logical that it is, since I see different behavior than 
> previously.  I've not turned off readahead or readahead_early yet, but 
> will do so shortly and see if I can tell any difference in model run 
> times which did increase after the kernel update.  One thing at a time I 
> guess :-)

Theoretically, there ought to be a decrease in startup times at certain
points _early_in_the_uptime_cycle. IMO, after a "steady state" typical
loading is achieved (hours, day, weeks??) there should be no or reduced
improvement (maybe decreased too *if* this forces some spurious swap
activity?).

*If* your config is anything similar to mine (or any generic?), I doubt
you'll find any long-term gain significant enough to warrant even the
near-zero maintenance of two more scripts and associated files.

It's the old "It doesn't cost me anything, but I get no benefit either"
routine. I almost always opt for excision of the wart. Sometimes that
costs later, but that's OK by me.

> 
> Sam
> 

-- 
Bill
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