linux-kernel - Re: [RFC] mm: remove swapcache page early

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Message-ID: <20130408014845.GB6394@blaptop>
Date:	Mon, 8 Apr 2013 10:48:45 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	Simon Jeons <simon.jeons@...il.com>
Cc:	Hugh Dickins <hughd@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Dan Magenheimer <dan.magenheimer@...cle.com>,
	Seth Jennings <sjenning@...ux.vnet.ibm.com>,
	Nitin Gupta <ngupta@...are.org>,
	Konrad Rzeszutek Wilk <konrad@...nok.org>,
	Shaohua Li <shli@...nel.org>,
	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [RFC] mm: remove swapcache page early

Hello Simon,

On Sun, Apr 07, 2013 at 03:26:12PM +0800, Simon Jeons wrote:
> Ping Minchan.
> On 04/02/2013 09:40 PM, Simon Jeons wrote:
> >Hi Hugh,
> >On 03/28/2013 05:41 AM, Hugh Dickins wrote:
> >>On Wed, 27 Mar 2013, Minchan Kim wrote:
> >>
> >>>Swap subsystem does lazy swap slot free with expecting the page
> >>>would be swapped out again so we can't avoid unnecessary write.
> >>                              so we can avoid unnecessary write.
> >
> >If page can be swap out again, which codes can avoid unnecessary
> >write? Could you point out to me? Thanks in advance. ;-)

Look at shrink_page_list.

1) PageAnon(page) && !PageSwapCache() 
2) add_to_swap's SetPageDirty
3) __remove_mapping

P.S)
It seems you are misunderstanding. Here isn't proper place to ask a
question for your understanding the code. As I know, there are some
project(ex, kernelnewbies) and books for study and sharing the
knowledge linux kernel.

I recommend Mel's "Understand the Linux Virtual Memory Manager".
It's rather outdated but will be very helpful to understand VM of
linux kernel. You can get it freely but I hope you pay for.
So if author become a billionaire by selecting best book in Amazon,
he might print out second edition which covers all of new VM features
and may solve all of you curiosity.

It would be a another method to contribute open source project. :)

I believe you talented developers can catch it up with reading the
code enoughly and find more bonus knowledge. I think it's why our senior
developers yell out RTFM and I follow them.

Cheers!

-- 
Kind regards,
Minchan Kim
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