Subject: Re: [PATCH] arm64: numa: rightsize the distance array

From: Jonathan Cameron <[email-masked]>
Date: Tue, 18 Aug 2020 18:13:53 +0100

On Fri, 24 Jul 2020 12:01:57 +0100
Jonathan Cameron <[email-masked]> wrote:

> On Wed, 8 Jul 2020 19:38:25 +0800
> Jonathan Cameron <[email-masked]> wrote:
> 
> > Unfortunately we are currently calling numa_alloc_distance well before we call
> > setup_node_to_cpu_mask_map means that nr_node_ids is set to MAX_NUMNODES.
> > This wastes a bit of memory and is confusing to the reader.
> > 
> > Note we could just decide to hardcode it as MAX_NUMNODES but if so we should
> > do so explicitly.
> > 
> > Looking at what x86 does, they do a walk of nodes_parsed and locally
> > establish the maximum node count seen.  We can't actually do that where we
> > were previously calling it in numa_init because nodes_parsed isn't set up
> > either yet.  So let us take a leaf entirely out of x86's book and make
> > the true assumption that nodes_parsed will definitely be set up before
> > we try to put a real value in this array.  Hence just do it on demand.
> > 
> > In order to avoid trying and failing to allocate the array multiple times
> > we do the same thing as x86 and set numa_distance = 1. This requires a
> > few small modifications elsewhere.
> > 
> > Worth noting, that with one exception (which it appears can be removed [1])
> > the x86 and arm numa distance code is now identical.  Worth factoring it
> > out to some common location?
> > 
> > [1] https://lkml.kernel.org/r/[email-masked]
> > 
> > Signed-off-by: Jonathan Cameron <[email-masked]>  
> 
> Polite nudge.  Anyone?  No particular urgency on this one but I'm thinking
> of taking a stab at factoring out this code into a common location for arm64
> and x86 and this change needs to proceed that.

This still applies cleanly post merge window, so still looking for some review!

Jonathan

> 
> Thanks,
> 
> Jonathan
> 
> 
> > ---
> > arch/arm64/mm/numa.c | 35 ++++++++++++++++++-----------------
> >  1 file changed, 18 insertions(+), 17 deletions(-)
> > 
> > diff --git a/arch/arm64/mm/numa.c b/arch/arm64/mm/numa.c
> > index aafcee3e3f7e..a2f549ef0a36 100644
> > --- a/arch/arm64/mm/numa.c
> > +++ b/arch/arm64/mm/numa.c
> > @@ -255,13 +255,11 @@ void __init numa_free_distance(void)
> >  {
> >  	size_t size;
> >  
> > -	if (!numa_distance)
> > -		return;
> > -
> >  	size = numa_distance_cnt * numa_distance_cnt *
> >  		sizeof(numa_distance[0]);
> > -
> > -	memblock_free(__pa(numa_distance), size);
> > +	/* numa_distance could be 1LU marking allocation failure, test cnt */
> > +	if (numa_distance_cnt)
> > +		memblock_free(__pa(numa_distance), size);
> >  	numa_distance_cnt = 0;
> >  	numa_distance = NULL;
> >  }
> > @@ -271,20 +269,29 @@ void __init numa_free_distance(void)
> >   */
> >  static int __init numa_alloc_distance(void)
> >  {
> > +	nodemask_t nodes_parsed;
> >  	size_t size;
> > +	int i, j, cnt = 0;
> >  	u64 phys;
> > -	int i, j;
> >  
> > -	size = nr_node_ids * nr_node_ids * sizeof(numa_distance[0]);
> > +	/* size the new table and allocate it */
> > +	nodes_parsed = numa_nodes_parsed;
> > +	for_each_node_mask(i, nodes_parsed)
> > +		cnt = i;
> > +	cnt++;
> > +	size = cnt * cnt * sizeof(numa_distance[0]);
> >  	phys = memblock_find_in_range(0, PFN_PHYS(max_pfn),
> >  				      size, PAGE_SIZE);
> > -	if (WARN_ON(!phys))
> > +	if (!phys) {
> > +		pr_warn("Warning: can't allocate distance table!\n");
> > +		/* don't retry until explicitly reset */
> > +		numa_distance = (void *)1LU;
> >  		return -ENOMEM;
> > -
> > +	}
> >  	memblock_reserve(phys, size);
> >  
> >  	numa_distance = __va(phys);
> > -	numa_distance_cnt = nr_node_ids;
> > +	numa_distance_cnt = cnt;
> >  
> >  	/* fill with the default distances */
> >  	for (i = 0; i < numa_distance_cnt; i++)
> > @@ -311,10 +318,8 @@ static int __init numa_alloc_distance(void)
> >   */
> >  void __init numa_set_distance(int from, int to, int distance)
> >  {
> > -	if (!numa_distance) {
> > -		pr_warn_once("Warning: distance table not allocated yet\n");
> > +	if (!numa_distance && numa_alloc_distance() < 0)
> >  		return;
> > -	}
> >  
> >  	if (from >= numa_distance_cnt || to >= numa_distance_cnt ||
> >  			from < 0 || to < 0) {
> > @@ -384,10 +389,6 @@ static int __init numa_init(int (*init_func)(void))
> >  	nodes_clear(node_possible_map);
> >  	nodes_clear(node_online_map);
> >  
> > -	ret = numa_alloc_distance();
> > -	if (ret < 0)
> > -		return ret;
> > -
> >  	ret = init_func();
> >  	if (ret < 0)
> >  		goto out_free_distance;  
> 
> 
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