Re: [PATCH 2/7] mm/init: remove the unnecessary special treatment for memory-less node

[Mike Rapoport <rppt@kernel.org>]

On Thu, Apr 04, 2024 at 11:23:51AM +0800, Baoquan He wrote:
> On 04/02/24 at 11:32am, Mike Rapoport wrote:
> > On Tue, Mar 26, 2024 at 02:11:28PM +0800, Baoquan He wrote:
> > > Because memory-less node's ->node_present_pages and its
> > > zone's ->present_pages are all 0, the judgement before calling
> > > node_set_state() to set N_MEMORY, N_HIGH_MEMORY, N_NORMAL_MEMORY for
> > > node is enough to skip memory-less node. The 'continue;' statement
> > > inside for_each_node() loop of free_area_init() is gilding the lily.
> > > 
> > > Here, remove the special handling to make memory-less node share the
> > > same code flow as normal node. And the code comment above the 'continue'
> > > statement is not needed either.
> > > 
> > > Signed-off-by: Baoquan He <bhe@redhat.com>
> > > ---
> > >  mm/mm_init.c | 18 +++---------------
> > >  1 file changed, 3 insertions(+), 15 deletions(-)
> > > 
> > > diff --git a/mm/mm_init.c b/mm/mm_init.c
> > > index 089dc60159e9..99681ffb9091 100644
> > > --- a/mm/mm_init.c
> > > +++ b/mm/mm_init.c
> > > @@ -1834,28 +1834,16 @@ void __init free_area_init(unsigned long *max_zone_pfn)
> > >  				panic("Cannot allocate %zuB for node %d.\n",
> > >  				       sizeof(*pgdat), nid);
> > >  			arch_refresh_nodedata(nid, pgdat);
> > > -			free_area_init_node(nid);
> > > -
> > > -			/*
> > > -			 * We do not want to confuse userspace by sysfs
> > > -			 * files/directories for node without any memory
> > > -			 * attached to it, so this node is not marked as
> > > -			 * N_MEMORY and not marked online so that no sysfs
> > > -			 * hierarchy will be created via register_one_node for
> > > -			 * it. The pgdat will get fully initialized by
> > > -			 * hotadd_init_pgdat() when memory is hotplugged into
> > > -			 * this node.
> > > -			 */
> > 
> > I think this comment is still valuable. Maybe rephrase it a bit and move it
> > before 'if (pgdat->node_present_pages)'?
> 
> Fair enough.
> 
> Do you think below paragraph is OK to you? Please help polish or
> rephrase it.
> 
> diff --git a/mm/mm_init.c b/mm/mm_init.c
> index dd875f943cbb..3ce0f29637ba 100644
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -1839,7 +1839,14 @@ void __init free_area_init(unsigned long *max_zone_pfn)
>  		pgdat = NODE_DATA(nid);
>  		free_area_init_node(nid);
>  
> -		/* Any memory on that node */
> +		/*
> +		 * No sysfs hierarcy will be created via register_one_node()
> +		 *for memory-less node because here it's not marked as N_MEMORY
> +		 *and won't be set online later. The benefit is userspace
> +		 *program won't be confused by sysfs files/directories of
> +		 *memory-less node. The pgdat will get fully initialized by
> +		 *hotadd_init_pgdat() when memory is hotplugged into this node.
> +		 */

Ack

>  		if (pgdat->node_present_pages) {
>  			node_set_state(nid, N_MEMORY);
>  			check_for_memory(pgdat);
> 

-- 
Sincerely yours,
Mike.