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

From: KOSAKI Motohiro
Date: Wed Dec 03 2008 - 10:12:28 EST

>> 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.

Ahhhhh, I did want to write "indirect access(or likes global variables)",
but my brain was sucked. sorry.

I'll post description fixed version soon. thanks.

>> 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?

Yeah, I think so.

>> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
> Acked-by: Rik van Riel <riel@xxxxxxxxxx>
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