linux-kernel - Re: [PATCH] mm/hugetlb: optimize the surplus state transfer code in move_hugetlb

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Date:   Fri, 12 Feb 2021 16:51:40 -0800
From:   Mike Kravetz <mike.kravetz@...cle.com>
To:     Miaohe Lin <linmiaohe@...wei.com>, akpm@...ux-foundation.org
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/hugetlb: optimize the surplus state transfer code in
 move_hugetlb_state()

On 2/9/21 11:12 PM, Miaohe Lin wrote:
> We should not transfer the per-node surplus state when we do not cross the
> node in order to save some cpu cycles
> 
> Signed-off-by: Miaohe Lin <linmiaohe@...wei.com>
> ---
>  mm/hugetlb.c | 6 ++++++
>  1 file changed, 6 insertions(+)

Thanks,

I was going to comment that the usual case is migrating to another node
and old_nid != new_nid.  However, this really is workload and system
configuration dependent.  In any case, the quick check is worth potentially
saving a lock/unlock cycle.

Reviewed-by: Mike Kravetz <mike.kravetz@...cle.com>
-- 
Mike Kravetz

> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index da347047ea10..4f2c92ddbca4 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -5632,6 +5632,12 @@ void move_hugetlb_state(struct page *oldpage, struct page *newpage, int reason)
>  		SetHPageTemporary(oldpage);
>  		ClearHPageTemporary(newpage);
>  
> +		/*
> +		 * There is no need to transfer the per-node surplus state
> +		 * when we do not cross the node.
> +		 */
> +		if (new_nid == old_nid)
> +			return;
>  		spin_lock(&hugetlb_lock);
>  		if (h->surplus_huge_pages_node[old_nid]) {
>  			h->surplus_huge_pages_node[old_nid]--;
>