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

[Rik van Riel <riel@redhat.com>]

KOSAKI Motohiro wrote:
> Hi
> 
> 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@jp.fujitsu.com>

Acked-by: Rik van Riel <riel@redhat.com>

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