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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>
Subject: Re: [PATCH 6/9] mm, page_alloc: simplify zonelist initialization
Date: Fri, 14 Jul 2017 15:18:23 +0100
Message-ID: <20170714141823.2j7t37t6zdzdf3sv@suse.de> (raw)
In-Reply-To: <20170714130242.GQ2618@dhcp22.suse.cz>

On Fri, Jul 14, 2017 at 03:02:42PM +0200, Michal Hocko wrote:
> > It *might* be safer given the next patch to zero out the remainder of
> > the _zonerefs to that there is no combination of node add/remove that has
> > an iterator working with a semi-valid _zoneref which is beyond the last
> > correct value. It *should* be safe as the very last entry will always
> > be null but if you don't zero it out, it is possible for iterators to be
> > working beyond the "end" of the zonelist for a short window.
> 
> yes that is true but there will always be terminating NULL zone and I
> found that acceptable. It is basically the same thing as accessing an
> empty zone or a zone twice. Or do you think this is absolutely necessary
> to handle?
> 

I don't think it's absolutely necessary. While you could construct some
odd behaviour for iterators currently past the end of the list, they would
eventually encounter a NULL.

> > Otherwise think it's ok including my stupid comment about node_order
> > stack usage.
> 
> What do you think about this on top?
> ---
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 49bade7ff049..3b98524c04ec 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -4913,20 +4913,21 @@ static int find_next_best_node(int node, nodemask_t *used_node_mask)
>   * This results in maximum locality--normal zone overflows into local
>   * DMA zone, if any--but risks exhausting DMA zone.
>   */
> -static void build_zonelists_in_node_order(pg_data_t *pgdat, int *node_order)
> +static void build_zonelists_in_node_order(pg_data_t *pgdat, int *node_order,
> +		unsigned nr_nodes)
>  {
>  	struct zonelist *zonelist;
> -	int i, zoneref_idx = 0;
> +	int i, nr_zones = 0;
>  
>  	zonelist = &pgdat->node_zonelists[ZONELIST_FALLBACK];
>  
> -	for (i = 0; i < MAX_NUMNODES; i++) {
> +	for (i = 0; i < nr_nodes; i++) {

The first iteration is then -- for (i = 0; i < 0; i++)

Fairly sure that's not what you meant.


>  		pg_data_t *node = NODE_DATA(node_order[i]);
>  
> -		zoneref_idx = build_zonelists_node(node, zonelist, zoneref_idx);
> +		nr_zones = build_zonelists_node(node, zonelist, nr_zones);

I meant converting build_zonelists_node and passing in &nr_zones and
returning false when an empty node is encountered. In this context,
it's also not about zones, it really is nr_zonerefs. Rename nr_zones in
build_zonelists_node as well.

-- 
Mel Gorman
SUSE Labs

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  reply index

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
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 [this message]
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 6/9] mm, page_alloc: simplify zonelist initialization Michal Hocko
2017-07-24  9:25   ` Vlastimil Babka

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