linux-kernel - Re: [PATCH 2/2] mm: forcely swapout when we are out of page cache

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Date:	Tue, 15 Jan 2013 16:09:57 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Minchan Kim <minchan@...nel.org>
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Sonny Rao <sonnyrao@...gle.com>,
	Bryan Freed <bfreed@...gle.com>,
	Hugh Dickins <hughd@...gle.com>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH 2/2] mm: forcely swapout when we are out of page cache

On Fri, 11 Jan 2013 13:43:27 +0900
Minchan Kim <minchan@...nel.org> wrote:

> Hi Andrew,
> 
> On Thu, Jan 10, 2013 at 01:58:28PM -0800, Andrew Morton wrote:
> > On Thu, 10 Jan 2013 11:23:06 +0900
> > Minchan Kim <minchan@...nel.org> wrote:
> > 
> > > > I have a feeling that laptop mode has bitrotted and these patches are
> > > > kinda hacking around as-yet-not-understood failures...
> > > 
> > > Absolutely, this patch is last guard for unexpectable behavior.
> > > As I mentioned in cover-letter, Luigi's problem could be solved either [1/2]
> > > or [2/2] but I wanted to add this as last resort in case of unexpected
> > > emergency. But you're right. It's not good to hide the problem like this path
> > > so let's drop [2/2].
> > > 
> > > Also, I absolutely agree it has bitrotted so for correcting it, we need a
> > > volunteer who have to inverstigate power saveing experiment with long time.
> > > So [1/2] would be band-aid until that.
> > 
> > I'm inclined to hold off on 1/2 as well, really.
> 
> Then, what's your plan?

My plan is to sit here until someone gets down and fully tests and
fixes laptop-mode.  Making it work properly, reliably and as-designed.

Or perhaps someone wants to make the case that we just don't need it
any more (SSDs are silent!) and removes it all.

> > 
> > The point of laptop_mode isn't to save power btw - it is to minimise
> > the frequency with which the disk drive is spun up.  By deferring and
> > then batching writeout operations, basically.
> 
> I don't get it. Why should we minimise such frequency?

Because my laptop was going clickety every minute and was keeping me
awake.

> It's for saving the power to increase batter life.

It might well have that effect, dunno.  That wasn't my intent.  Testing
needed!

> As I real all document about laptop_mode, they all said about the power
> or battery life saving.
> 
> 1. Documentation/laptops/laptop-mode.txt
> 2. http://linux.die.net/man/8/laptop_mode
> 3. http://samwel.tk/laptop_mode/
> 3. http://www.thinkwiki.org/wiki/Laptop-mode 

Documentation creep ;)

Ten years ago, gad: http://lwn.net/Articles/1652/
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