linux-kernel - Re: [PATCH 0/6] Page I/O

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Message-ID: <x49ha9bhnc8.fsf@segfault.boston.devel.redhat.com>
Date:	Fri, 10 Jan 2014 10:24:07 -0500
From:	Jeff Moyer <jmoyer@...hat.com>
To:	Matthew Wilcox <matthew.r.wilcox@...el.com>
Cc:	linux-fsdevel@...r.kernel.org, linux-mm@...r.kernel.org,
	linux-kernel@...r.kernel.org, axboe@...nel.dk
Subject: Re: [PATCH 0/6] Page I/O

Matthew Wilcox <matthew.r.wilcox@...el.com> writes:

> This patch set implements pageio as I described in my talk at
> Linux.Conf.AU.  It's for review more than application, I think
> benchmarking is going to be required to see if it's a win.  We've done
> some benchmarking with an earlier version of the patch and a Chatham card,
> and it's a win for us.
>
> The fundamental point of these patches is that we *can* do I/O without
> allocating a BIO (or request, or ...) and so we can end up doing fun
> things like swapping out a page without allocating any memory.
>
> Possibly it would be interesting to do sub-page I/Os (ie change the
> rw_page prototype to take a 'start' and 'length' instead of requiring the
> I/O to be the entire page), but the problem then arises about what the
> 'done' callback should be.

For those of us who were not fortunate enough to attend your talk, would
mind providing some background, like why you went down this path in the
first place, and maybe what benchmarks you ran where you found it "a
win?"

Another code path making an end-run around the block layer is
interesting, but may keep cgroup I/O throttling from working properly,
for example.

Cheers,
Jeff
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