linux-kernel - Re: [PATCH 1/9] mm, page_alloc: rip out ZONELIST_ORDER

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Date:   Fri, 14 Jul 2017 13:56:16 +0100
From:   Mel Gorman <mgorman@...e.de>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        LKML <linux-kernel@...r.kernel.org>, linux-api@...r.kernel.org
Subject: Re: [PATCH 1/9] mm, page_alloc: rip out ZONELIST_ORDER_ZONE

On Fri, Jul 14, 2017 at 01:38:40PM +0200, Michal Hocko wrote:
> On Fri 14-07-17 12:16:33, Mel Gorman wrote:
> > On Fri, Jul 14, 2017 at 12:47:57PM +0200, Michal Hocko wrote:
> > > > That should to be "default" because the original code would have the proc
> > > > entry display "default" unless it was set at runtime. Pretty weird I
> > > > know but it's always possible someone is parsing the original default
> > > > and not handling it properly.
> > > 
> > > Ohh, right! That is indeed strange. Then I guess it would be probably
> > > better to simply return Node to make it clear what the default is. What
> > > do you think?
> > > 
> > 
> > That would work too. The casing still matches.
> 
> This folded in?
> ---
> From c7c36f011590680b254813be00ed791ddbc1bf1c Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@...e.com>
> Date: Fri, 14 Jul 2017 13:36:05 +0200
> Subject: [PATCH] fold me "mm, page_alloc: rip out ZONELIST_ORDER_ZONE"
> 
> - do not print Default in sysctl handler because our behavior was rather
> inconsistent in the past numa_zonelist_order was lowecase while
> zonelist_order_name was uppercase so boot time unchanged value woul
> print lowercase while updated value could be uppercase. Print "Node"
> which is the default instead - Mel
> 
> Signed-off-by: Michal Hocko <mhocko@...e.com>
> ---
>  mm/page_alloc.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index dd4c96edcec3..49bade7ff049 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4828,8 +4828,8 @@ int numa_zonelist_order_handler(struct ctl_table *table, int write,
>  	int ret;
>  
>  	if (!write) {
> -		int len = sizeof("Default");
> -		if (copy_to_user(buffer, "Default", len))
> +		int len = sizeof("Node");
> +		if (copy_to_user(buffer, "Node", len))
>  			return -EFAULT;

Ok for the name. But what's with using sizeof? The type is char * so it
just happens to work for Default, but not for Node. Also strongly suggest
you continue using proc_dostring because it catches all the corner-cases
that can occur.

-- 
Mel Gorman
SUSE Labs