linux-kernel - Re: [RFC][PATCH 5/5] (experimental) chase and free cache only swap

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Message-Id: <20090527103107.9c04eb55.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Wed, 27 May 2009 10:31:07 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Johannes Weiner <hannes@...xchg.org>
Cc:	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
	"nishimura@....nes.nec.co.jp" <nishimura@....nes.nec.co.jp>,
	"hugh.dickins@...cali.co.uk" <hugh.dickins@...cali.co.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH 5/5] (experimental) chase and free cache only swap

On Wed, 27 May 2009 03:26:58 +0200
Johannes Weiner <hannes@...xchg.org> wrote:

> On Wed, May 27, 2009 at 09:08:13AM +0900, KAMEZAWA Hiroyuki wrote:
> > On Tue, 26 May 2009 20:14:00 +0200
> > Johannes Weiner <hannes@...xchg.org> wrote:
> > 
> > > On Tue, May 26, 2009 at 12:18:34PM +0900, KAMEZAWA Hiroyuki wrote:
> > > > 
> > > > From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> > > > 
> > > > Just a trial/example patch.
> > > > I'd like to consider more. Better implementation idea is welcome.
> > > > 
> > > > When the system does swap-in/swap-out repeatedly, there are 
> > > > cache-only swaps in general.
> > > > Typically,
> > > >  - swapped out in past but on memory now while vm_swap_full() returns true
> > > > pages are cache-only swaps. (swap_map has no references.)
> > > > 
> > > > This cache-only swaps can be an obstacles for smooth page reclaiming.
> > > > Current implemantation is very naive, just scan & free.
> > > 
> > > I think we can just remove that vm_swap_full() check in do_swap_page()
> > > and try to remove the page from swap cache unconditionally.
> > > 
> > I'm not sure why reclaim swap entry only at write fault.
> 
> How do you come to that conclusion?  Do you mean the current code does
> that? 
yes.

2474         pte = mk_pte(page, vma->vm_page_prot);
2475         if (write_access && reuse_swap_page(page)) {
2476                 pte = maybe_mkwrite(pte_mkdirty(pte), vma);
2477                 write_access = 0;
2478         }


> Did you understand that I suggested that?
> 

I thought you suggested that swp_entry should be reclaimed in read-fault as
same way as write-fault.

Thanks,
-Kame




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