Re: drain_node_pages: interrupt latency reduction / optimization

[Andrew Morton <akpm@osdl.org>]

Christoph Lameter <clameter@sgi.com> wrote:
>
> Here is a fixup adding some comments and raw_smp_processor_id()
> 
> Signed-off-by: Christoph Lameter <clameter@sgi.com>
> 
> Index: linux-2.6/mm/page_alloc.c
> ===================================================================
> --- linux-2.6.orig/mm/page_alloc.c	2006-03-10 16:09:10.000000000 -0800
> +++ linux-2.6/mm/page_alloc.c	2006-03-10 16:10:07.000000000 -0800
> @@ -593,6 +593,8 @@ static int rmqueue_bulk(struct zone *zon
>  /*
>   * Called from the slab reaper to drain pagesets on a particular node that
>   * belong to the currently executing processor.
> + * Note that this function must be called with the thread pinned to
> + * a processor.
>   */
>  void drain_node_pages(int nodeid)
>  {
> @@ -603,7 +605,7 @@ void drain_node_pages(int nodeid)
>  		struct zone *zone = NODE_DATA(nodeid)->node_zones + z;
>  		struct per_cpu_pageset *pset;
>  
> -		pset = zone_pcp(zone, smp_processor_id());
> +		pset = zone_pcp(zone, raw_smp_processor_id());
>  		for (i = 0; i < ARRAY_SIZE(pset->pcp); i++) {
>  			struct per_cpu_pages *pcp;

hm.  That replaces a runtime check with a comment.  If someone comes along
and reuses this function wrongly they'll have a nasty subtle bug.

IOW: it might be best to keep the smp_processor_id() check in there.

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