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Re: [GIT PULL] mm: frontswap (for 3.2 window)

From:  Andrew Morton <akpm-AT-linux-foundation.org>
To:  Dan Magenheimer <dan.magenheimer-AT-oracle.com>
Subject:  Re: [GIT PULL] mm: frontswap (for 3.2 window)
Date:  Tue, 1 Nov 2011 14:43:09 -0700
Message-ID:  <20111101144309.a51c99b5.akpm@linux-foundation.org>
Cc:  KAMEZAWA Hiroyuki <kamezawa.hiroyu-AT-jp.fujitsu.com>, Linus Torvalds <torvalds-AT-linux-foundation.org>, linux-mm-AT-kvack.org, LKML <linux-kernel-AT-vger.kernel.org>, Konrad Wilk <konrad.wilk-AT-oracle.com>, Jeremy Fitzhardinge <jeremy-AT-goop.org>, Seth Jennings <sjenning-AT-linux.vnet.ibm.com>, ngupta-AT-vflare.org, levinsasha928-AT-gmail.com, Chris Mason <chris.mason-AT-oracle.com>, JBeulich-AT-novell.com, Dave Hansen <dave-AT-linux.vnet.ibm.com>, Jonathan Corbet <corbet-AT-lwn.net>, Neo Jia <cyclonusj-AT-gmail.com>
Archive-link:  Article

On Tue, 1 Nov 2011 08:25:38 -0700 (PDT)
Dan Magenheimer <dan.magenheimer@oracle.com> wrote:

> OK, I will then coordinate with sfr to remove it from the linux-next
> tree when (if?) akpm puts the patchset into the -mm tree.

No, that's not necessary.  The current process (you maintain git tree,
it gets included in -next, later gets pulled by Linus) is good.  The
only reason I see for putting such code through -mm would be if there
were significant interactions with other core MM work.

It doesn't matter which route is taken, as long as the code is
appropriately reviewed and tested.

>  But
> since very few linux-mm experts had responded to previous postings
> of the frontswap patchset, I am glad to have a much wider audience
> to discuss it now because of the lkml git-pull request.

At kernel summit there was discussion and overall agreement that we've
been paying insufficient attention to the big-picture "should we
include this feature at all" issues.  We resolved to look more
intensely and critically at new features with a view to deciding
whether their usefulness justified their maintenance burden.  It seems
that you're our crash-test dummy ;) (Now I'm wondering how to get
"cgroups: add a task counter subsystem" put through the same wringer).

I will confess to and apologise for dropping the ball on cleancache and
frontswap.  I was never really able to convince myself that it met the
(very vague) cost/benefit test, but nor was I able to present
convincing arguments that it failed that test.  So I very badly went
into hiding, to wait and see what happened.  What we needed all those
months ago was to have the discussion we're having now.

This is a difficult discussion and a difficult decision.  But it is
important that we get it right.  Thanks for you patience.

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