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From: Jeff Moyer <jmoyer@redhat.com>
To: "Jason B. Akers" <jason.b.akers@intel.com>
Cc: linux-ide@vger.kernel.org, axboe@fb.com, kapil.karkra@intel.com,
        dan.j.williams@intel.com, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 1/5] block, ioprio: include caching advice via ionice
References: <20141029180454.4879.75088.stgit@stg-AndroidDev-VirtualBox>
	<20141029182345.4879.98373.stgit@stg-AndroidDev-VirtualBox>
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X-PCLoadLetter: What the f**k does that mean?
Date: Wed, 29 Oct 2014 15:02:42 -0400
In-Reply-To: <20141029182345.4879.98373.stgit@stg-AndroidDev-VirtualBox>
	(Jason B. Akers's message of "Wed, 29 Oct 2014 11:23:45 -0700")
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"Jason B. Akers" <jason.b.akers@intel.com> writes:

> From: Dan Williams <dan.j.williams@intel.com>
>
> Steal one unused bit from the priority class and two bits from the
> priority data, to implement a 3 bit cache-advice field.  Similar to the
> page cache advice from fadvise() these hints are meant to be consumed
> by hybrid drives.  Solid State Hyrbid-Drives, as defined by the SATA-IO
> Specification, implement up to a 4-bit cache priority that can be
> specified along with a FPDMA command.

ionice is about setting an I/O scheduling class for a *process*.  So,
unless I've missed something, this does not seem like the right
interface for passing I/O hints.

You mention fadvise hints, which sounds like a good fit (and madvise
would be equally interesting), but I don't see where you've wired them
up in this patch set.  Did I miss it?

Cheers,
Jeff