linux-kernel - Re: [Lsf-pc] [LSF/MM TOPIC] really large storage sectors

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Message-ID: <20140122143452.GW4963@suse.de>
Date:	Wed, 22 Jan 2014 14:34:52 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Ric Wheeler <rwheeler@...hat.com>
Cc:	linux-scsi@...r.kernel.org, linux-ide@...r.kernel.org,
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	lsf-pc@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [Lsf-pc] [LSF/MM TOPIC] really large storage sectors - going
 beyond 4096 bytes

On Wed, Jan 22, 2014 at 09:10:48AM -0500, Ric Wheeler wrote:
> On 01/22/2014 04:34 AM, Mel Gorman wrote:
> >On Tue, Jan 21, 2014 at 10:04:29PM -0500, Ric Wheeler wrote:
> >>One topic that has been lurking forever at the edges is the current
> >>4k limitation for file system block sizes. Some devices in
> >>production today and others coming soon have larger sectors and it
> >>would be interesting to see if it is time to poke at this topic
> >>again.
> >>
> >Large block support was proposed years ago by Christoph Lameter
> >(http://lwn.net/Articles/232757/). I think I was just getting started
> >in the community at the time so I do not recall any of the details. I do
> >believe it motivated an alternative by Nick Piggin called fsblock though
> >(http://lwn.net/Articles/321390/). At the very least it would be nice to
> >know why neither were never merged for those of us that were not around
> >at the time and who may not have the chance to dive through mailing list
> >archives between now and March.
> >
> >FWIW, I would expect that a show-stopper for any proposal is requiring
> >high-order allocations to succeed for the system to behave correctly.
> >
> 
> I have a somewhat hazy memory of Andrew warning us that touching
> this code takes us into dark and scary places.
> 

That is a light summary. As Andrew tends to reject patches with poor
documentation in case we forget the details in 6 months, I'm going to guess
that he does not remember the details of a discussion from 7ish years ago.
This is where Andrew swoops in with a dazzling display of his eidetic
memory just to prove me wrong.

Ric, are there any storage vendor that is pushing for this right now?
Is someone working on this right now or planning to? If they are, have they
looked into the history of fsblock (Nick) and large block support (Christoph)
to see if they are candidates for forward porting or reimplementation?
I ask because without that person there is a risk that the discussion
will go as follows

Topic leader: Does anyone have an objection to supporting larger block
	sizes than the page size?
Room: Send patches and we'll talk.

-- 
Mel Gorman
SUSE Labs
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