linux-kernel - Re: [PATCH 1/1 v3] drivers/nvme: default to 4k device page size

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Message-ID: <20151103134624.GG13904@localhost.localdomain>
Date:	Tue, 3 Nov 2015 13:46:25 +0000
From:	Keith Busch <keith.busch@...el.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>, aik@...abs.ru,
	linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
	paulus@...ba.org, sparclinux@...r.kernel.org,
	willy@...ux.intel.com, linuxppc-dev@...ts.ozlabs.org,
	David Miller <davem@...emloft.net>, david@...son.dropbear.id.au
Subject: Re: [PATCH 1/1 v3] drivers/nvme: default to 4k device page size

On Tue, Nov 03, 2015 at 05:18:24AM -0800, Christoph Hellwig wrote:
> On Fri, Oct 30, 2015 at 02:35:11PM -0700, Nishanth Aravamudan wrote:
> > diff --git a/drivers/block/nvme-core.c b/drivers/block/nvme-core.c
> > index ccc0c1f93daa..a9a5285bdb39 100644
> > --- a/drivers/block/nvme-core.c
> > +++ b/drivers/block/nvme-core.c
> > @@ -1717,7 +1717,12 @@ static int nvme_configure_admin_queue(struct nvme_dev *dev)
> >  	u32 aqa;
> >  	u64 cap = readq(&dev->bar->cap);
> >  	struct nvme_queue *nvmeq;
> > -	unsigned page_shift = PAGE_SHIFT;
> > +	/*
> > +	 * default to a 4K page size, with the intention to update this
> > +	 * path in the future to accomodate architectures with differing
> > +	 * kernel and IO page sizes.
> > +	 */
> > +	unsigned page_shift = 12;
> >  	unsigned dev_page_min = NVME_CAP_MPSMIN(cap) + 12;
> >  	unsigned dev_page_max = NVME_CAP_MPSMAX(cap) + 12;
> 
> Looks good as a start.  Note that all the MPSMIN/MAX checking could
> be removed as NVMe devices must support 4k pages.

MAX can go, and while it's probably the case that all devices support 4k,
it's not a spec requirement, so we should keep the dev_page_min check.
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