linux-kernel - Re: [PATCH] mm/memory_hotplug: drain per-cpu pages again during memory offline

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Message-ID: <20200903070733.GO4617@dhcp22.suse.cz>
Date:   Thu, 3 Sep 2020 09:07:33 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Pavel Tatashin <pasha.tatashin@...een.com>
Cc:     linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        linux-mm@...ck.org
Subject: Re: [PATCH] mm/memory_hotplug: drain per-cpu pages again during
 memory offline

On Tue 01-09-20 08:46:15, Pavel Tatashin wrote:
[...]
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index e9d5ab5d3ca0..d6d54922bfce 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1575,6 +1575,15 @@ static int __ref __offline_pages(unsigned long start_pfn,
>  		/* check again */
>  		ret = walk_system_ram_range(start_pfn, end_pfn - start_pfn,
>  					    NULL, check_pages_isolated_cb);
> +		/*
> +		 * per-cpu pages are drained in start_isolate_page_range, but if
> +		 * there are still pages that are not free, make sure that we
> +		 * drain again, because when we isolated range we might
> +		 * have raced with another thread that was adding pages to
> +		 * pcp list.

I would also add
		 * Forward progress should be still guaranteed because
		 * pages on the pcp list can only belong to MOVABLE_ZONE
		 * because has_unmovable_pages explicitly checks for
		 * PageBuddy on freed pages on other zones.
> +		 */
> +		if (ret)
> +			drain_all_pages(zone);
>  	} while (ret);
>  
>  	/* Ok, all of our target is isolated.
> -- 
> 2.25.1
> 

-- 
Michal Hocko
SUSE Labs