linux-kernel - Re: [RFC PATCH 0/14] Parallel memory initialisation

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Date:	Thu, 16 Apr 2015 00:25:01 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Linux-MM <linux-mm@...ck.org>, Robin Holt <holt@....com>,
	Nathan Zimmer <nzimmer@....com>, Daniel Rahn <drahn@...e.com>,
	Davidlohr Bueso <dbueso@...e.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Tom Vaden <tom.vaden@...com>,
	Scott Norton <scott.norton@...com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 0/14] Parallel memory initialisation

On Mon, 13 Apr 2015 11:16:52 +0100 Mel Gorman <mgorman@...e.de> wrote:

> Memory initialisation

I wish we didn't call this "memory initialization".  Because memory
initialization is memset(), and that isn't what we're doing here.

Installation?  Bringup?

> had been identified as one of the reasons why large
> machines take a long time to boot. Patches were posted a long time ago
> that attempted to move deferred initialisation into the page allocator
> paths. This was rejected on the grounds it should not be necessary to hurt
> the fast paths to parallelise initialisation. This series reuses much of
> the work from that time but defers the initialisation of memory to kswapd
> so that one thread per node initialises memory local to that node. The
> issue is that on the machines I tested with, memory initialisation was not
> a major contributor to boot times. I'm posting the RFC to both review the
> series and see if it actually helps users of very large machines.
> 
> ...
>
>  15 files changed, 507 insertions(+), 98 deletions(-)

Sadface at how large and complex this is.  I'd hoped the way we were
going to do this was by bringing up a bit of memory to get booted up,
then later on we just fake a bunch of memory hot-add operations.  So
the new code would be pretty small and quite high-level.
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