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

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Message-ID: <alpine.LSU.2.00.1203081758490.18195@eggly.anvils>
Date:	Thu, 8 Mar 2012 18:06:50 -0800 (PST)
From:	Hugh Dickins <hughd@...gle.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.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 Thu, 8 Mar 2012, KAMEZAWA Hiroyuki wrote:
> On Tue, 6 Mar 2012 19:22:21 -0800 (PST)
> Hugh Dickins <hughd@...gle.com> wrote:
> > 
> > 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;

Yes, that would have been a good compromise (given a better name
than "tmp_var"!), I didn't realize that one was acceptable to you.

But I see that Konstantin has been inspired by our disagreement to a
more creative solution.

I like very much the look of what he's come up with, but I'm still
puzzling over why it barely makes any improvement to __isolate_lru_page():
seems significantly inferior (in code size terms) to his original (which
I imagine Glauber's compromise would be equivalent to).

At some point I ought to give up on niggling about this,
but I haven't quite got there yet.

Hugh
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