linux-kernel - Re: [PATCH v3 07/26] mm: drop CONFIG_HAVE_ARCH_NODEDATA

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Message-ID: <ZrDkLeLxQAVvZcBn@kernel.org>
Date: Mon, 5 Aug 2024 17:39:41 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org,
	Alexander Gordeev <agordeev@...ux.ibm.com>,
	Andreas Larsson <andreas@...sler.com>,
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	Christophe Leroy <christophe.leroy@...roup.eu>,
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Subject: Re: [PATCH v3 07/26] mm: drop CONFIG_HAVE_ARCH_NODEDATA_EXTENSION

On Sun, Aug 04, 2024 at 04:11:19PM +0100, Jonathan Cameron wrote:
> On Sun, 4 Aug 2024 10:24:15 +0300
> Mike Rapoport <rppt@...nel.org> 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 <Jonathan.Cameron@...wei.com> 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 :)

Right :)

I'll post v4 after kbuild confirms it compiles :)
 
> 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
> > 
> >  
> > 
> 
> 

-- 
Sincerely yours,
Mike.