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Date:   Thu, 27 Jan 2022 09:28:17 +0100
From:   Michal Hocko <mhocko@suse.com>
To:     Wei Yang <richard.weiyang@gmail.com>
Cc:     akpm@linux-foundation.org, mgorman@techsingularity.net,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mm/memory_hotplug: build zonelist for managed_zone
Message-ID: <YfJXoSVkQ3X5u44F@dhcp22.suse.cz>
References: <20220127012023.18095-1-richard.weiyang@gmail.com>
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On Thu 27-01-22 01:20:23, Wei Yang wrote:
> During memory hotplug, when online/offline a zone, we need to rebuild
> the zonelist for all node. There are two checks to decide whether a zone
> would be added to zonelist:
> 
>   * one in online_pages/offline_pages to decide necessity
>   * one in build_zonerefs_node to do real add
> 
> Currently we use different criteria at these two places, which is
> different from the original behavior.
> 
> Originally during memory hotplug, zonelist is re-built when zone hasn't
> been populated. This in introduced in 'commit 6811378e7d8b ("[PATCH]
> wait_table and zonelist initializing for memory hotadd: update zonelists")'.
> And at that moment, build_zonelists_node() also use populated_zone() to
> decide whether the zone should be added to zonelist.
> 
> While in 'commit 6aa303defb74 ("mm, vmscan: only allocate and reclaim
> from zones with pages managed by the buddy allocator")',
> build_zonelists_node() changed to use managed_zone() to add zonelist.
> But we still use populated_zone() to decide the necessity.
> 
> This patch restore the original behavior by using the same criteria to
> add a zone in zonelist during memory hotplug.

Why?

> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
> Fixes: 6aa303defb74 ("mm, vmscan: only allocate and reclaim from zones with pages managed by the buddy allocator")
> CC: Mel Gorman <mgorman@techsingularity.net>
> ---
>  mm/memory_hotplug.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index 2a9627dc784c..8f1906b33937 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1102,11 +1102,11 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
>  	spin_unlock_irqrestore(&zone->lock, flags);
>  
>  	/*
> -	 * If this zone is not populated, then it is not in zonelist.
> +	 * If this zone is not managed, then it is not in zonelist.
>  	 * This means the page allocator ignores this zone.
>  	 * So, zonelist must be updated after online.
>  	 */
> -	if (!populated_zone(zone)) {
> +	if (!managed_zone(zone)) {
>  		need_zonelists_rebuild = 1;
>  		setup_zone_pageset(zone);
>  	}
> @@ -1985,7 +1985,7 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages,
>  	/* reinitialise watermarks and update pcp limits */
>  	init_per_zone_wmark_min();
>  
> -	if (!populated_zone(zone)) {
> +	if (!managed_zone(zone)) {
>  		zone_pcp_reset(zone);
>  		build_all_zonelists(NULL);
>  	}
> -- 
> 2.33.1

-- 
Michal Hocko
SUSE Labs