linux-kernel - Re: [resend PATCH v2 11/33] dm: add dax_device and dax

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Message-ID: <1501258623.2413.3.camel@wdc.com>
Date:   Fri, 28 Jul 2017 16:17:07 +0000
From:   Bart Van Assche <Bart.VanAssche@....com>
To:     "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>
CC:     "dm-devel@...hat.com" <dm-devel@...hat.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "toshi.kani@....com" <toshi.kani@....com>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "hch@....de" <hch@....de>,
        "snitzer@...hat.com" <snitzer@...hat.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: Re: [resend PATCH v2 11/33] dm: add dax_device and dax_operations
 support

On Mon, 2017-04-17 at 12:09 -0700, Dan Williams wrote:
> diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
> index b7767da50c26..1de8372d9459 100644
> --- a/drivers/md/Kconfig
> +++ b/drivers/md/Kconfig
> @@ -200,6 +200,7 @@ config BLK_DEV_DM_BUILTIN
>  config BLK_DEV_DM
>  	tristate "Device mapper support"
>  	select BLK_DEV_DM_BUILTIN
> +	select DAX
>  	---help---
>  	  Device-mapper is a low level volume manager.  It works by allowing
>  	  people to specify mappings for ranges of logical sectors.  Various

(replying to an e-mail of three months ago)

Hello Dan,

While building a v4.12 kernel I noticed that enabling device mapper support
now unconditionally enables DAX. I think there are plenty of systems that use
dm but do not need DAX. Have you considered to rework this such that instead
of dm selecting DAX that DAX support is only enabled in dm if CONFIG_DAX is
enabled?

Thanks,

Bart.