try_to_swap_out: to aggressive in dropping pte's?

try_to_swap_out: to aggressive in dropping pte's?

[Benjamin Redelings I]

Hello,
	I was wondering if anybody could explain why we try to drop the pte on a 
page if it is not pte_young, even if it has a high age and has the 
referenced bit set?

	Also, does anybody have any thoughts on how to decouple scanning the page 
tables for hardward referenced bits, and doing swap-out?  On one of my 
128mb boxes, linus's changes to only run swap_out when there is memory 
pressure make things MUCH more interactive and decreased unnecessary 
swapping.  However, this means that the page tables are not scanned, 
which is not good...

	On a related note, in 2.4.10-pre10, Linus makes pages get deactivated in 
try_to_swap_out if !PageReferenced(page), thus making page->age almost 
irrelevant.  I would like to make a quick hack hybrid approach that 
keeps lots of the 2.4.10-pre10 vm changes still uses age information on 
the active list.  This probably isn't adequate, but how about:

1. change "if (ptep_test_and_clear_young(page_table))" to
"if (ptep_test_and_clear_young(page_table) ||
	PageTestandClearReference(page))"

2. revert Linus's change in pre10 to deactivate pages if age==0 instead 
of if !PageReference.

thanks for any suggestions,
-BenRI
-- 
"I will begin again" - U2, 'New Year's Day'
Benjamin Redelings I      <><     http://www.bol.ucla.edu/~bredelin/

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