linux-kernel - Re: [HMM 01/16] mm/memory/hotplug: convert device bool to int to allow for more flags v3

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Message-ID: <20170319200821.GB2774@techsingularity.net>
Date:   Sun, 19 Mar 2017 20:08:21 +0000
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     J?r?me Glisse <jglisse@...hat.com>
Cc:     akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, John Hubbard <jhubbard@...dia.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        David Nellans <dnellans@...dia.com>,
        Russell King <linux@...linux.org.uk>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        Chris Metcalf <cmetcalf@...lanox.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [HMM 01/16] mm/memory/hotplug: convert device bool to int to
 allow for more flags v3

On Thu, Mar 16, 2017 at 12:05:20PM -0400, J?r?me Glisse wrote:
> When hotpluging memory we want more informations on the type of memory and
> its properties. Replace the device boolean flag by an int and define a set
> of flags.
> 
> New property for device memory is an opt-in flag to allow page migration
> from and to a ZONE_DEVICE. Existing user of ZONE_DEVICE are not expecting
> page migration to work for their pages. New changes to page migration i
> changing that and we now need a flag to explicitly opt-in page migration.
> 
> Changes since v2:
>   - pr_err() in case of hotplug failure
> 
> Changes since v1:
>   - Improved commit message
>   - Improved define name
>   - Improved comments
>   - Typos
> 
> Signed-off-by: Jérôme Glisse <jglisse@...hat.com>

Fairly minor but it's standard for flags to be unsigned due to
uncertainity about what happens when a signed type is bit shifted.
May not apply to your case but fairly trivial to address.