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

[Baoquan He <bhe@redhat.com>]

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.
+		 */
 		if (pgdat->node_present_pages) {
 			node_set_state(nid, N_MEMORY);
 			check_for_memory(pgdat);