linux-kernel - Re: [patch 05/19] split LRU lists into anon & file sets

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Date:	Tue, 15 Jan 2008 08:57:11 +0900
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Rik van Riel <riel@...hat.com>
Cc:	kosaki.motohiro@...fujitsu.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Lee Schermerhorn <Lee.Schermerhorn@...com>
Subject: Re: [patch 05/19] split LRU lists into anon & file sets

Hi

> > Why drop (total_swap_pages == 0 && PageAnon(page)) condition?
> > in embedded sysmtem, 
> > CONFIG_NORECLAIM is OFF (because almost embedded cpu is 32bit) and
> > that anon move to inactive list is meaningless because it doesn't have swap.
> 
> That was a mistake, kind of.  Since all swap backed pages are on their
> own LRU lists, we should not scan those lists at all any more if we are
> out of swap space.
> 
> The patch that fixes get_scan_ratio() adds that test.
> 
> Having said that, with the nr_swap_pages==0 test in get_scan_ratio(),
> we no longer need to test for that condition in shrink_active_list().

Oh I see!
thank you for your kindful lecture.

your implementation is very cute.


> > below code is more good, may be.
> > but I don't understand yet why ignore page_referenced() result at anon page ;-)
> 
> On modern systems, swapping out anonymous pages is a relatively rare
> event.  All anonymous pages start out as active and referenced, so
> testing for that condition does (1) not add any information and (2)
> mean we need to scan ALL of the anonymous pages, in order to find one
> candidate to swap out (since they are all referenced).
> 
> Simply deactivating a few pages and checking whether they were referenced
> again while on the (smaller) inactive_anon_list means we can find candidates
> to page out with a lot less CPU time used.

thanks, I understand, may be.


- kosaki

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