linux-kernel - Re: [PATCH 3/7 v2] mm: rework __isolate_lru

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Message-Id: <20120308143034.f3521b1e.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Thu, 8 Mar 2012 14:30:34 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Johannes Weiner <jweiner@...hat.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/7 v2] mm: rework __isolate_lru_page() file/anon filter

On Tue, 6 Mar 2012 19:22:21 -0800 (PST)
Hugh Dickins <hughd@...gle.com> wrote:

> On Sat, 3 Mar 2012, Konstantin Khlebnikov wrote:
> 
> > This patch adds file/anon filter bits into isolate_mode_t,
> > this allows to simplify checks in __isolate_lru_page().
> > 
> > v2:
> > * use switch () instead of if ()
> > * fixed lumpy-reclaim isolation mode
> > 
> > Signed-off-by: Konstantin Khlebnikov <khlebnikov@...nvz.org>
> 
> I'm sorry to be messing you around on this one, Konstantin, but...
> 
> (a) if you do go with the switch statements,
> in kernel we align the "case"s underneath the "switch"
> 
> but
> 
> (b) I seem to be at odds with Kamezawa-san, I much preferred your
> original, which did in 2 lines what the switches do in 10 lines.
> And I'd say there's more opportunity for error in 10 lines than 2.
> 
> What does the compiler say (4.5.1 here, OPTIMIZE_FOR_SIZE off)?
>    text	   data	    bss	    dec	    hex	filename
>   17723	    113	     17	  17853	   45bd	vmscan.o.0
>   17671	    113	     17	  17801	   4589	vmscan.o.1
>   17803	    113	     17	  17933	   460d	vmscan.o.2
> 
> That suggests that your v2 is the worst and your v1 the best.
> Kame, can I persuade you to let the compiler decide on this?
> 

Hmm. How about Costa' proposal ? as

int tmp_var = PageActive(page) ? ISOLATE_ACTIVE : ISOLATE_INACTIVE
if (!(mode & tmp_var))
    ret;

Thanks,
-Kame


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