Subject: Re: [PATCH v3 07/26] mm: drop CONFIG_HAVE_ARCH_NODEDATA_EXTENSION

From: Jonathan Cameron <[email-masked]>
Date: Sun, 4 Aug 2024 16:11:19 +0100

On Sun, 4 Aug 2024 10:24:15 +0300
Mike Rapoport <[email-masked]> wrote:

> On Sat, Aug 03, 2024 at 11:58:13AM -0700, Andrew Morton wrote:
> > On Fri, 2 Aug 2024 10:49:22 +0100 Jonathan Cameron <[email-masked]> wrote:
> >   
> > > > --- a/mm/mm_init.c
> > > > +++ b/mm/mm_init.c
> > > > @@ -1838,11 +1838,10 @@ void __init free_area_init(unsigned long *max_zone_pfn)
> > > >  
> > > >  		if (!node_online(nid)) {
> > > >  			/* Allocator not initialized yet */
> > > > -			pgdat = arch_alloc_nodedata(nid);
> > > > +			pgdat = memblock_alloc(sizeof(*pgdat), SMP_CACHE_BYTES);
> > > >  			if (!pgdat)
> > > >  				panic("Cannot allocate %zuB for node %d.\n",
> > > >  				       sizeof(*pgdat), nid);
> > > > -			arch_refresh_nodedata(nid, pgdat);  
> > > 
> > > This allocates pgdat but never sets node_data[nid] to it
> > > and promptly leaks it on the line below. 
> > > 
> > > Just to sanity check this I spun up a qemu machine with no memory
> > > initially present on some nodes and it went boom as you'd expect.
> > > 
> > > I tested with addition of
> > > 			NODE_DATA(nid) = pgdat;
> > > and it all seems to work as expected.  
> > 
> > Thanks, I added that.  It blew up on x86_64 allnoconfig because
> > node_data[] (and hence NODE_DATA()) isn't an lvalue when CONFIG_NUMA=n.
> > 
> > I'll put some #ifdef CONFIG_NUMAs in there for now but
> > 
> > a) NODE_DATA() is upper-case. Implies "constant".  Shouldn't be assigned to.
> > 
> > b) NODE_DATA() should be non-lvalue when CONFIG_NUMA=y also.  But no,
> >    we insist on implementing things in cpp instead of in C.  
> 
> This looks like a candidate for a separate tree-wide cleanup.
>  
> > c) In fact assigning to anything which ends in "()" is nuts.  Please
> >    clean up my tempfix.
> > 
> > c) Mike, generally I'm wondering if there's a bunch of code here
> >    which isn't needed on CONFIG_NUMA=n.  Please check all of this for
> >    unneeded bloatiness.  
> 
> I believe the patch addresses your concerns, just with this the commit log
> needs update. Instead of 
> 
>     Replace the call to arch_alloc_nodedata() in free_area_init() with
>     memblock_alloc(), remove arch_refresh_nodedata() and cleanup
>     include/linux/memory_hotplug.h from the associated ifdefery.
> 
> it should be
> 
>     Replace the call to arch_alloc_nodedata() in free_area_init() with a
>     new helper alloc_offline_node_data(), remove arch_refresh_nodedata()
>     and cleanup include/linux/memory_hotplug.h from the associated
>     ifdefery.
> 
> I can send an updated patch if you prefer.
This solution looks good to me - except for a Freudian typo that means it won't
compile :)

Jonathan

> 
> diff --git a/include/linux/numa.h b/include/linux/numa.h
> index 3b12d8ca0afd..5a749fd67f39 100644
> --- a/include/linux/numa.h
> +++ b/include/linux/numa.h
> @@ -34,6 +34,7 @@ extern struct pglist_data *node_data[];
>  #define NODE_DATA(nid)	(node_data[nid])
>  
>  void __init alloc_node_data(int nid);
> +void __init alloc_offline_node_data(int nit);
>  
>  /* Generic implementation available */
>  int numa_nearest_node(int node, unsigned int state);
> @@ -62,6 +63,8 @@ static inline int phys_to_target_node(u64 start)
>  {
>  	return 0;
>  }
> +
> +static inline void alloc_offline_node_data(int nit) {}
nid
>  #endif
>  
>  #define numa_map_to_online_node(node) numa_nearest_node(node, N_ONLINE)
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index bcc2f2dd8021..2785be04e7bb 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -1836,13 +1836,8 @@ void __init free_area_init(unsigned long *max_zone_pfn)
>  	for_each_node(nid) {
>  		pg_data_t *pgdat;
>  
> -		if (!node_online(nid)) {
> -			/* Allocator not initialized yet */
> -			pgdat = memblock_alloc(sizeof(*pgdat), SMP_CACHE_BYTES);
> -			if (!pgdat)
> -				panic("Cannot allocate %zuB for node %d.\n",
> -				       sizeof(*pgdat), nid);
> -		}
> +		if (!node_online(nid))
> +			alloc_offline_node_data(nid);
>  
>  		pgdat = NODE_DATA(nid);
>  		free_area_init_node(nid);
> diff --git a/mm/numa.c b/mm/numa.c
> index da27eb151dc5..07e486a977c7 100644
> --- a/mm/numa.c
> +++ b/mm/numa.c
> @@ -34,6 +34,18 @@ void __init alloc_node_data(int nid)
>  	memset(NODE_DATA(nid), 0, sizeof(pg_data_t));
>  }
>  
> +void __init alloc_offline_node_data(int nit)

nid

> +{
> +	pg_data_t *pgdat;
> +
> +	pgdat = memblock_alloc(sizeof(*pgdat), SMP_CACHE_BYTES);
> +	if (!pgdat)
> +		panic("Cannot allocate %zuB for node %d.\n",
> +		      sizeof(*pgdat), nid);
> +
> +	node_data[nid] = pgdat;
> +}
> +
>  /* Stub functions: */
>  
>  #ifndef memory_add_physaddr_to_nid
> 
>  
>