Re: [PATCH] vmscan: improve reclaim throuput to bail out patch

From: Rik van Riel
Date: Wed Dec 03 2008 - 08:46:48 EST

KOSAKI Motohiro wrote:

I evaluate rvr bailout and skip-freeing patch in this week conteniously.
I'd like to dump first output here.

Rik, could you please review following?
vmscan bail out patch move nr_reclaimed variable to struct scan_control.
Unfortunately, indirect access can easily happen cache miss.
More unfortunately, Some architecture (e.g. ia64) don't access global
variable so fast.

That is amazing. Especially considering that the scan_control
is a local variable on the stack.

if heavy memory pressure happend, that's ok.
cache miss already plenty. it is not observable.

but, if memory pressure is lite, performance degression is obserbable.

about 4-5% degression.

Then, this patch introduce temporal local variable.

OK. the degression is disappeared.

I can't argue with the numbers, though :)

Maybe all the scanning we do ends up evicting the cache lines
with the scan_control struct in it from the fast part of the
CPU cache?

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>

Acked-by: Rik van Riel <riel@xxxxxxxxxx>

All rights reversed.
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at