Re: [PATCH] mm, memory_hotplug: update pcp lists everytime onlining a memory block
From: David Hildenbrand
Date: Mon Aug 03 2020 - 04:05:41 EST
On 02.08.20 14:54, Charan Teja Reddy wrote:
> When onlining a first memory block in a zone, pcp lists are not updated
> thus pcp struct will have the default setting of ->high = 0,->batch = 1.
> This means till the second memory block in a zone(if it have) is onlined
> the pcp lists of this zone will not contain any pages because pcp's
> ->count is always greater than ->high thus free_pcppages_bulk() is
> called to free batch size(=1) pages every time system wants to add a
> page to the pcp list through free_unref_page(). To put this in a word,
> system is not using benefits offered by the pcp lists when there is a
> single onlineable memory block in a zone. Correct this by always
> updating the pcp lists when memory block is onlined.
I guess such setups are rare ... but I can imagine it being the case
with virtio-mem in the future ... not 100% if this performance
optimization is really relevant in practice ... how did you identify this?
> Signed-off-by: Charan Teja Reddy <charante@xxxxxxxxxxxxxx>
> mm/memory_hotplug.c | 3 +--
> 1 file changed, 1 insertion(+), 2 deletions(-)
> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> index dcdf327..7f62d69 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -854,8 +854,7 @@ int __ref online_pages(unsigned long pfn, unsigned long nr_pages,
> node_states_set_node(nid, &arg);
> if (need_zonelists_rebuild)
> - else
> - zone_pcp_update(zone);
> + zone_pcp_update(zone);
Does, in general, look sane to me.
Reviewed-by: David Hildenbrand <david@xxxxxxxxxx>
David / dhildenb