Re: [PATCH v2 resend] mm/memory_hotplug: Make unpopulated zones PCP structures unreachable during hot remove

[Oscar Salvador]

On Mon, Apr 12, 2021 at 01:08:42PM +0100, Mel Gorman wrote:
> zone_pcp_reset allegedly protects against a race with drain_pages
> using local_irq_save but this is bogus. local_irq_save only operates
> on the local CPU. If memory hotplug is running on CPU A and drain_pages
> is running on CPU B, disabling IRQs on CPU A does not affect CPU B and
> offers no protection.
> 
> This patch deletes IRQ disable/enable on the grounds that IRQs protect
> nothing and assumes the existing hotplug paths guarantees the PCP cannot be
> used after zone_pcp_enable(). That should be the case already because all
> the pages have been freed and there is no page to put on the PCP lists.
> 
> Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>

Reviewed-by: Oscar Salvador <osalvador@xxxxxxx>

-- 
Oscar Salvador
SUSE L3