linux-kernel - Re: [PATCH 2/3] mm/memory_hotplug: fix potential permanent lru cache disable

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Date:   Mon, 23 Aug 2021 11:15:40 +0200
From:   Oscar Salvador <osalvador@...e.de>
To:     Miaohe Lin <linmiaohe@...wei.com>
Cc:     akpm@...ux-foundation.org, naoya.horiguchi@....com,
        mhocko@...e.com, minchan@...nel.org, cgoldswo@...eaurora.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] mm/memory_hotplug: fix potential permanent lru cache
 disable

On 2021-08-21 11:42, Miaohe Lin wrote:
> If offline_pages failed after lru_cache_disable(), it forgot to do
> lru_cache_enable() in error path. So we would have lru cache disabled
> permanently in this case.
> 
> Fixes: d479960e44f2 ("mm: disable LRU pagevec during the migration 
> temporarily")
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>

Reviewed-by: Oscar Salvador <osalvador@...e.de>

Should this go to stable?
In case we fail to enable it again, we will bypass the pvec cache 
anytime we add a new page to the LRU which might lead to severe 
performance regression?

> ---
>  mm/memory_hotplug.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index d986d3791986..9fd0be32a281 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -2033,6 +2033,7 @@ int __ref offline_pages(unsigned long start_pfn,
> unsigned long nr_pages,
>  	undo_isolate_page_range(start_pfn, end_pfn, MIGRATE_MOVABLE);
>  	memory_notify(MEM_CANCEL_OFFLINE, &arg);
>  failed_removal_pcplists_disabled:
> +	lru_cache_enable();
>  	zone_pcp_enable(zone);
>  failed_removal:
>  	pr_debug("memory offlining [mem %#010llx-%#010llx] failed due to 
> %s\n",

-- 
Oscar Salvador
SUSE L3