Re: [PATCH *] rmap VM 11c (RMAP IS A WINNER!)

[Adam Kropelin]

(Andrea, the previous version of this mail wasn't supposed to go out yet. I
fat-fingered and sent it before I was done. This is the full version.)

Andrea Arcangeli:
> On Sat, Jan 19, 2002 at 01:39:22PM -0500, Adam Kropelin wrote:
> > Andrea Arcangeli:
> > > With -aa something sane along the above lines is:
> > >
> > > /bin/echo "10 2000 0 0 500 3000 30 5 0" > /proc/sys/vm/bdflush
> >
> > Unfortunately, those adjustments on top of 2.4.18-pre2aa2 set a new record
for
> > worst performance: 7:19.
>
> then please try to decrease the nfract variable again, the above set it
> to 2000, if you've a slow harddisk maybe that's too much, so you can try
> to set it to 500 again.

Yes, the harddisk is definitely slow: it's a hw RAID5 partition with older
drives, so writes are pretty slow.

I tried various nfract settings:

/bin/echo "10 300 0 0 500 3000 30 5 0" > /proc/sys/vm/bdflush
7:33

/bin/echo "10 500 0 0 500 3000 30 5 0" > /proc/sys/vm/bdflush
6:00

/bin/echo "10 800 0 0 500 3000 30 5 0" > /proc/sys/vm/bdflush
7:17

nfract=500 seems to be the best and gets much closer to the performance of rmap
and -ac. Writeout is still very bursty compared to the other kernels, but that
may not really matter, I don't know.

> I'd also give a try with the below settings:
>
> /bin/echo "10 500 0 0 500 3000 80 8 0" > /proc/sys/vm/bdflush

7:08

<snip>

> Also just in case, I'd suggest to try to repeat each benchmark three
> times, so we know we are not bitten by random variations in the numbers.

I've been doing a variation on that theme already. The numbers I've been
reporting are best of 2 runs. I have never seen the 2 runs differ by more than
+/- 10 seconds.

--Adam