Re: [PATCH 1/1] Balance Freeing of Huge Pages across Nodes

[David Rientjes <rientjes@google.com>]

On Fri, 26 Jun 2009, Lee Schermerhorn wrote:

> [PATCH] 1/1 Balance Freeing of Huge Pages across Nodes
> 
> Against:  12jun09 mmotm
> 
> [applies to 25jun09 mmotm as well]
> 
> Free huges pages from nodes in round robin fashion in an
> attempt to keep [persistent a.k.a static] hugepages balanced
> across nodes
> 
> New function free_pool_huge_page() is modeled on and
> performs roughly the inverse of alloc_fresh_huge_page().
> Replaces dequeue_huge_page() which now has no callers,
> so this patch removes it.
> 
> Helper function hstate_next_node_to_free() uses new hstate
> member next_to_free_nid to distribute "frees" across all
> nodes with huge pages.
> 
> V2:
> 
> At Mel Gorman's suggestion:  renamed hstate_next_node() to
> hstate_next_node_to_alloc() for symmetry.  Also, renamed
> hstate member hugetlb_next_node to next_node_to_free.
> ["hugetlb" is implicit in the hstate struct, I think].
> 
> New in this version:
> 
> Modified adjust_pool_surplus() to use hstate_next_node_to_alloc()
> and hstate_next_node_to_free() to advance node id for adjusting
> surplus huge page count, as this is equivalent to allocating and
> freeing persistent huge pages.  [Can't blame Mel for this part.]
> 
> Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>

Acked-by: David Rientjes <rientjes@google.com>

Very useful change!

> @@ -666,14 +648,15 @@ static int alloc_fresh_huge_page(struct 
>  	int next_nid;
>  	int ret = 0;
>  
> -	start_nid = h->hugetlb_next_nid;
> +	start_nid = h->next_nid_to_alloc;
> +	next_nid = start_nid;
>  
>  	do {
> -		page = alloc_fresh_huge_page_node(h, h->hugetlb_next_nid);
> +		page = alloc_fresh_huge_page_node(h, next_nid);
>  		if (page)
>  			ret = 1;
> -		next_nid = hstate_next_node(h);
> -	} while (!page && h->hugetlb_next_nid != start_nid);
> +		next_nid = hstate_next_node_to_alloc(h);
> +	} while (!page && next_nid != start_nid);
>  
>  	if (ret)
>  		count_vm_event(HTLB_BUDDY_PGALLOC);

This actually puts the currently unused next_nid to use, nice.

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