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From: Mel Gorman <mgorman@suse.de>
To: Michal Hocko <mhocko@kernel.org>
Cc: linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
	Johannes Weiner <hannes@cmpxchg.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	LKML <linux-kernel@vger.kernel.org>,
	Michal Hocko <mhocko@suse.com>,
	linux-api@vger.kernel.org
Subject: Re: [PATCH 1/9] mm, page_alloc: rip out ZONELIST_ORDER_ZONE
Date: Fri, 14 Jul 2017 10:36:50 +0100
Message-ID: <20170714093650.l67vbem2g4typkta@suse.de> (raw)
In-Reply-To: <20170714080006.7250-2-mhocko@kernel.org>

On Fri, Jul 14, 2017 at 09:59:58AM +0200, Michal Hocko wrote:
> From: Michal Hocko <mhocko@suse.com>
> 
> Supporting zone ordered zonelists costs us just a lot of code while
> the usefulness is arguable if existent at all. Mel has already made
> node ordering default on 64b systems. 32b systems are still using
> ZONELIST_ORDER_ZONE because it is considered better to fallback to
> a different NUMA node rather than consume precious lowmem zones.
> 
> This argument is, however, weaken by the fact that the memory reclaim
> has been reworked to be node rather than zone oriented. This means
> that lowmem requests have to skip over all highmem pages on LRUs already
> and so zone ordering doesn't save the reclaim time much. So the only
> advantage of the zone ordering is under a light memory pressure when
> highmem requests do not ever hit into lowmem zones and the lowmem
> pressure doesn't need to reclaim.
> 
> Considering that 32b NUMA systems are rather suboptimal already and
> it is generally advisable to use 64b kernel on such a HW I believe we
> should rather care about the code maintainability and just get rid of
> ZONELIST_ORDER_ZONE altogether. Keep systcl in place and warn if
> somebody tries to set zone ordering either from kernel command line
> or the sysctl.
> 
> Cc: <linux-api@vger.kernel.org>
> Signed-off-by: Michal Hocko <mhocko@suse.com>
> index 80e4adb4c360..d9f4ea057e74 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4864,40 +4824,22 @@ int numa_zonelist_order_handler(struct ctl_table *table, int write,
>  		void __user *buffer, size_t *length,
>  		loff_t *ppos)
>  {
> -	char saved_string[NUMA_ZONELIST_ORDER_LEN];
> +	char *str;
>  	int ret;
> -	static DEFINE_MUTEX(zl_order_mutex);
>  
> -	mutex_lock(&zl_order_mutex);
> -	if (write) {
> -		if (strlen((char *)table->data) >= NUMA_ZONELIST_ORDER_LEN) {
> -			ret = -EINVAL;
> -			goto out;
> -		}
> -		strcpy(saved_string, (char *)table->data);
> +	if (!write) {
> +		int len = sizeof("Default");
> +		if (copy_to_user(buffer, "Default", len))
> +			return -EFAULT;
> +		return len;
>  	}

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.

Otherwise I think we're way past the point where large memory 32-bit
NUMA machines are a thing so

Acked-by: Mel Gorman <mgorman@suse.de>

-- 
Mel Gorman
SUSE Labs

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Thread overview: 55+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-07-14  7:59 [PATCH 0/9] cleanup zonelists initialization Michal Hocko
2017-07-14  7:59 ` [PATCH 1/9] mm, page_alloc: rip out ZONELIST_ORDER_ZONE Michal Hocko
2017-07-14  9:36   ` Mel Gorman [this message]
2017-07-14 10:47     ` Michal Hocko
2017-07-14 11:16       ` Mel Gorman
2017-07-14 11:38         ` Michal Hocko
2017-07-14 12:56           ` Mel Gorman
2017-07-14 13:01             ` Mel Gorman
2017-07-14 13:08             ` Michal Hocko
2017-07-19  9:33   ` Vlastimil Babka
2017-07-19 13:44     ` Michal Hocko
2017-07-14  7:59 ` [PATCH 2/9] mm, page_alloc: remove boot pageset initialization from memory hotplug Michal Hocko
2017-07-14  9:39   ` Mel Gorman
2017-07-19 13:15   ` Vlastimil Babka
2017-07-14  8:00 ` [PATCH 3/9] mm, page_alloc: do not set_cpu_numa_mem on empty nodes initialization Michal Hocko
2017-07-14  9:48   ` Mel Gorman
2017-07-14 10:50     ` Michal Hocko
2017-07-14 12:32       ` Mel Gorman
2017-07-14 12:39         ` Michal Hocko
2017-07-14 12:56           ` Mel Gorman
2017-07-19 13:19   ` Vlastimil Babka
2017-07-14  8:00 ` [PATCH 4/9] mm, memory_hotplug: drop zone from build_all_zonelists Michal Hocko
2017-07-19 13:33   ` Vlastimil Babka
2017-07-20  8:15     ` Michal Hocko
2017-07-14  8:00 ` [PATCH 5/9] mm, memory_hotplug: remove explicit build_all_zonelists from try_online_node Michal Hocko
2017-07-14 12:14   ` Michal Hocko
2017-07-20  6:13   ` Vlastimil Babka
2017-07-14  8:00 ` [PATCH 6/9] mm, page_alloc: simplify zonelist initialization Michal Hocko
2017-07-14  9:55   ` Mel Gorman
2017-07-14 10:51     ` Michal Hocko
2017-07-14 12:46   ` Mel Gorman
2017-07-14 13:02     ` Michal Hocko
2017-07-14 14:18       ` Mel Gorman
2017-07-17  6:06         ` Michal Hocko
2017-07-17  8:07           ` Mel Gorman
2017-07-17  8:19             ` Michal Hocko
2017-07-17  8:58               ` Mel Gorman
2017-07-17  9:15                 ` Michal Hocko
2017-07-20  6:55   ` Vlastimil Babka
2017-07-20  7:19     ` Michal Hocko
2017-07-14  8:00 ` [PATCH 7/9] mm, page_alloc: remove stop_machine from build_all_zonelists Michal Hocko
2017-07-14  9:59   ` Mel Gorman
2017-07-14 11:00     ` Michal Hocko
2017-07-14 12:47       ` Mel Gorman
2017-07-14 11:29   ` Vlastimil Babka
2017-07-14 11:43     ` Michal Hocko
2017-07-14 11:45       ` Michal Hocko
2017-07-20  6:16         ` Vlastimil Babka
2017-07-20  7:24   ` Vlastimil Babka
2017-07-20  9:21     ` Michal Hocko
2017-07-14  8:00 ` [PATCH 8/9] mm, memory_hotplug: get rid of zonelists_mutex Michal Hocko
2017-07-14  8:00 ` [PATCH 9/9] mm, sparse, page_ext: drop ugly N_HIGH_MEMORY branches for allocations Michal Hocko
2017-07-20  8:04   ` Vlastimil Babka
2017-07-21 14:39 [PATCH -v1 0/9] cleanup zonelists initialization Michal Hocko
2017-07-21 14:39 ` [PATCH 1/9] mm, page_alloc: rip out ZONELIST_ORDER_ZONE Michal Hocko
2017-07-21 14:45   ` Michal Hocko

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