linux-kernel - Re: [PATCH] mm/mempolicy.c: forbid static or relative flags for local NUMA mode

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Date:   Tue, 20 Sep 2016 17:12:16 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Piotr Kwapulinski <kwapulinski.piotr@...il.com>,
        akpm@...ux-foundation.org
Cc:     kirill.shutemov@...ux.intel.com, rientjes@...gle.com,
        mhocko@...nel.org, mgorman@...hsingularity.net,
        liangchen.linux@...il.com, nzimmer@....com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Linux API <linux-api@...r.kernel.org>,
        linux-man@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH] mm/mempolicy.c: forbid static or relative flags for local
 NUMA mode

[CC += linux-api@...r.kernel.org]

     Since this is a kernel-user-space API change, please CC linux-api@. The 
kernel source file Documentation/SubmitChecklist notes that all Linux kernel 
patches that change userspace interfaces should be CCed to 
linux-api@...r.kernel.org, so that the various parties who are interested in API 
changes are informed. For further information, see 
https://www.kernel.org/doc/man-pages/linux-api-ml.html

I think man page should document the change? Also I noticed that MPOL_NUMA 
itself is missing in the man page...

On 09/18/2016 01:29 PM, Piotr Kwapulinski wrote:
> The MPOL_F_STATIC_NODES and MPOL_F_RELATIVE_NODES flags are irrelevant
> when setting them for MPOL_LOCAL NUMA memory policy via set_mempolicy.
> Return the "invalid argument" from set_mempolicy whenever
> any of these flags is passed along with MPOL_LOCAL.
> It is consistent with MPOL_PREFERRED passed with empty nodemask.
> It also slightly shortens the execution time in paths where these flags
> are used e.g. when trying to rebind the NUMA nodes for changes in
> cgroups cpuset mems (mpol_rebind_preferred()) or when just printing
> the mempolicy structure (/proc/PID/numa_maps).

Hmm not sure I understand. How does change in mpol_new() affect 
mpol_rebind_preferred()?

Vlastimil

> Isolated tests done.
>
> Signed-off-by: Piotr Kwapulinski <kwapulinski.piotr@...il.com>
> ---
>  mm/mempolicy.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 2da72a5..27b07d1 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -276,7 +276,9 @@ static struct mempolicy *mpol_new(unsigned short mode, unsigned short flags,
>  				return ERR_PTR(-EINVAL);
>  		}
>  	} else if (mode == MPOL_LOCAL) {
> -		if (!nodes_empty(*nodes))
> +		if (!nodes_empty(*nodes) ||
> +		    (flags & MPOL_F_STATIC_NODES) ||
> +		    (flags & MPOL_F_RELATIVE_NODES))
>  			return ERR_PTR(-EINVAL);
>  		mode = MPOL_PREFERRED;
>  	} else if (nodes_empty(*nodes))
>