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

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Date:	Tue, 3 Nov 2015 05:18:24 -0800
From:	Christoph Hellwig <hch@...radead.org>
To:	Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>
Cc:	"Busch, Keith" <keith.busch@...el.com>, aik@...abs.ru,
	linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
	Christoph Hellwig <hch@...radead.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 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.
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