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

[Adam Kropelin]

Ken Brownfield:

> Do you get more even throughput with this:
>
> /bin/echo "10 0 0 0 500 3000 10 0 0" > /proc/sys/vm/bdflush
>
> It seems to help significantly for me under heavy sustained I/O load.

With a little modification, Ken's suggestion makes -rmap11c a winner on my test
case.

/bin/echo "10 0 0 0 500 3000 30 0 0" > /proc/sys/vm/bdflush

Switching to synchronous bdflush a little later than Ken did brings performance
up to ~2000 blocks/sec, which is similar to older -ac kernels. This writeout
rate is very consistent (even more so than -ac) and seems to be the top end in
all large writes to the RAID (tried FTP, samba, and local balls-to-the-wall "cat
/dev/zero >..."), which helps show that this is not a network driver or protocol
interaction.

The same bdflush tuning (leaving aa's additional parameters at their defaults)
on 2.4.18pre2aa2 yields some improvement, but rmap is consistently faster by a
good margin. 2.4.17 performs worse with this tuning and is pretty much eating
dust at this point.

Latest Results:
2.4.17-rmap11c: 5:41 (down from 6:58)
2.4.18-pre2aa2: 6:31 (down from 7:10)
2.4.17: 7:06 (up from 6:57)

Congrats, Rik and thanks, Ken!

--Adam