Re: [PATCH 2/2] mem-hotplug: Fix wrong check for zone->pageset initialization in online_pages().

[Tang Chen <tangchen@cn.fujitsu.com>]

On 11/05/2014 09:01 AM, Kamezawa Hiroyuki wrote:
> ......
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 3ab01b2..bc0de0f 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1013,9 +1013,13 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages, int online_typ
>   	 * If this zone is not populated, then it is not in zonelist.
>   	 * This means the page allocator ignores this zone.
>   	 * So, zonelist must be updated after online.
> +	 *
> +	 * If this zone is populated, zone->pageset could be initialized
> +	 * to boot_pageset for the first time a node is added. If so,
> +	 * zone->pageset should be allocated.
>   	 */
>   	mutex_lock(&zonelists_mutex);
> -	if (!populated_zone(zone)) {
> +	if (!populated_zone(zone) || !zone_pcp_initialized(zone)) {
> Please don't add another strange meanings to zone's pcplist.
>
> If you say zone->present_pages doesn't mean zone has pages in buddy list any more,
> please rewrite all parts using zone->present_pages including populated_zone().

Adding Liu Jiang...

I think zone->managed_pages was introduced by Liu Jiang in the following
patch:

>From 9feedc9d831e18ae6d0d15aa562e5e46ba53647b Mon Sep 17 00:00:00 2001
From: Jiang Liu <liuj97@gmail.com>
Date: Wed, 12 Dec 2012 13:52:12 -0800
Subject: [PATCH 1/1] mm: introduce new field "managed_pages" to struct zone

Before this patch, zone->present_pages meant "amount of memory
(excluding holes)",
not the zone has pages in buddy system.

So I think zone->present_pages keeps its meaning as before. But it may
be abused
somewhere else, such as here.

> I think there are several parts calculates parameters based on present_pages.
>
> I myself doesn't welcome having both of compliated "managed pages" and "present pages"...
>
> How about adding 
>
> static inline int managed_zone(struct zone *zone)
> {
> 	return (!!zone->managed_pages);
> }
>
> for this bug fix ?

Yes, adding this function could fix this problem.

And by the way, we have the following code in onine_pages():

zone->present_pages += onlined_pages;

pgdat_resize_lock(zone->zone_pgdat, &flags);
zone->zone_pgdat->node_present_pages += onlined_pages;
pgdat_resize_unlock(zone->zone_pgdat, &flags);

We should do this when the zone size is changed, not where it is now.
Will send patches for this soon.

Thanks.

>
> Other parts, using present_pages, should be considered well.
>
>