linux-kernel - Re: [PATCH v7] NVMe: conversion to blk-mq

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Date:	Tue, 10 Jun 2014 17:33:33 -0400
From:	Matthew Wilcox <willy@...ux.intel.com>
To:	Keith Busch <keith.busch@...el.com>
Cc:	Jens Axboe <axboe@...com>,
	Matias Bjørling <m@...rling.me>,
	"sbradshaw@...ron.com" <sbradshaw@...ron.com>,
	"tom.leiming@...il.com" <tom.leiming@...il.com>,
	"hch@...radead.org" <hch@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>
Subject: Re: [PATCH v7] NVMe: conversion to blk-mq

On Tue, Jun 10, 2014 at 03:21:18PM -0600, Keith Busch wrote:
> Yeah, nvme_setup_prps is probably the least readable code in this driver.
> Maybe some comments are in order here...
> 
> There are two rules for an SGL to be mappable to a PRP:
> 
> 1. Every element must have zero page offset, except the first.
> 
> 2. Every element must end on a page boundary, except the last.

Or to put it another way, NVMe PRPs only support I/Os that describe a
single range of virtual memory.

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