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

[Oscar Salvador]

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@xxxxxxxxxx>

Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>

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