linux-kernel - Re: [RFC PATCH 0/7] Non-blockling buffered fs read (page cache only)

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Message-ID: <CANP1eJG0CDtAA-7q3MvQE7Fz0=awYu0V4p43w-1vw2oV=gg-qQ@mail.gmail.com>
Date:	Mon, 22 Sep 2014 13:02:03 -0400
From:	Milosz Tanski <milosz@...in.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Jeff Moyer <jmoyer@...hat.com>,
	"Elliott, Robert (Server Storage)" <Elliott@...com>,
	Andreas Dilger <adilger@...ger.ca>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-aio@...ck.org" <linux-aio@...ck.org>,
	Mel Gorman <mgorman@...e.de>,
	Volker Lendecke <Volker.Lendecke@...net.de>,
	Tejun Heo <tj@...nel.org>
Subject: Re: [RFC PATCH 0/7] Non-blockling buffered fs read (page cache only)

I'll send out the next RFC with 2 syscalls and magic position values.
I'm waiting for Jeff to chime in on the v2 patchset before I send out
the next one.

On Mon, Sep 22, 2014 at 12:42 PM, Christoph Hellwig <hch@...radead.org> wrote:
> On Mon, Sep 22, 2014 at 12:32:02PM -0400, Milosz Tanski wrote:
>> I spent some time thinking about multi-position scatter/gather in
>> context of this over the weekend. The non-blocking case seams easy,
>> the implementation I purposed needs an extra loop. Where this gets
>> hairy is making the non-trivial blocking case work well (as in have
>> concurrent requests for each of the ranges) in the filesystem code. If
>> that's the road we're going to go down I have a gut feeling we're
>> going to get stuck in the same spot(s) as the other non-blocking
>> buffered r/w attempts from the past.
>
> The other thing sis that we have a basically ready, easy to use
> implementation of flagged I/O (my name for the new syscalls), while
> S/G I/O will take forever to discuss and is the natual vehicle for
> other extensions like T10 DIX.
>
> I'd like to suggest you consolidate your syscalls down from 4 to 2
> as suggestes by overloading the negative offset argument, giving
> us two more syscalls slows for S/G once it's ready.  Note that
> a sync S/G syscalls should of course also support these flags, although
> I suspect the primary use cases for S/G I/O would be through the aio
> machinery.



-- 
Milosz Tanski
CTO
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New York, NY 10016

p: 646-253-9055
e: milosz@...in.com
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