linux-kernel - Re: [PATCH 2/3] mm/compaction: add and use for_each_populated_zone

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Date: Thu, 14 Mar 2024 22:38:35 -0700
From: Luis Chamberlain <mcgrof@...nel.org>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc: akpm@...ux-foundation.org, jhubbard@...dia.com, vbabka@...e.cz,
	mgorman@...e.de, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	dave@...olabs.net, p.raghav@...sung.com, da.gomez@...sung.com
Subject: Re: [PATCH 2/3] mm/compaction: add and use
 for_each_populated_zone_pgdat() helper

On Thu, Mar 14, 2024 at 03:19:45PM +0800, Baolin Wang wrote:
> 
> 
> On 2024/3/14 08:54, Luis Chamberlain wrote:
> > We can just wrap most of the work done on fragmentation_score_node()
> > into a pgdat helper for populated zones. Add the helper and use it.
> > 
> > Signed-off-by: Luis Chamberlain <mcgrof@...nel.org>
> > ---
> >   include/linux/mmzone.h | 8 ++++++++
> >   mm/compaction.c        | 9 ++-------
> >   2 files changed, 10 insertions(+), 7 deletions(-)
> > 
> > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> > index a497f189d988..1fd74c7100ec 100644
> > --- a/include/linux/mmzone.h
> > +++ b/include/linux/mmzone.h
> > @@ -1597,6 +1597,14 @@ extern struct zone *next_zone(struct zone *zone);
> >   			; /* do nothing */		\
> >   		else
> > +#define for_each_populated_zone_pgdat(zone, pgdat)	\
> > +	for (zone = pgdat->node_zones;			\
> > +	     zone;					\
> > +	     zone = next_zone(zone))			\
> > +		if (!populated_zone(zone))		\
> > +			; /* do nothing */		\
> > +		else
> 
> I think this will break the original logics, since the next_zone() will
> iterate over all memory zones, instead of only the memory zones of the
> specified node.

Definitely, thanks, so we'd need something like this in addition:

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 34b729fc751b..bd11d33ea14d 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -1568,6 +1568,7 @@ static inline struct pglist_data *NODE_DATA(int nid)
 extern struct pglist_data *first_online_pgdat(void);
 extern struct pglist_data *next_online_pgdat(struct pglist_data *pgdat);
 extern struct zone *next_zone(struct zone *zone);
+extern struct zone *next_zone_pgdat(struct zone *zone, struct pglist_data *pgdat);
 
 /**
  * for_each_online_pgdat - helper macro to iterate over all online nodes
@@ -1600,7 +1601,7 @@ extern struct zone *next_zone(struct zone *zone);
 #define for_each_populated_zone_pgdat(zone, pgdat)	\
 	for (zone = pgdat->node_zones;			\
 	     zone;					\
-	     zone = next_zone(zone))			\
+	     zone = next_zone_pgdat(zone, pgdat))	\
 		if (!populated_zone(zone))		\
 			; /* do nothing */		\
 		else
diff --git a/mm/compaction.c b/mm/compaction.c
index 015126803017..96434f6fc1ad 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -2152,7 +2152,6 @@ static unsigned int fragmentation_score_node(pg_data_t *pgdat)
 {
 	unsigned int score = 0;
 	struct zone *zone;
-	int zoneid;
 
 	for_each_populated_zone_pgdat(zone, pgdat)
 		score += fragmentation_score_zone_weighted(zone);
diff --git a/mm/mmzone.c b/mm/mmzone.c
index c01896eca736..043a6dc16c05 100644
--- a/mm/mmzone.c
+++ b/mm/mmzone.c
@@ -43,6 +43,18 @@ struct zone *next_zone(struct zone *zone)
 	return zone;
 }
 
+/*
+ * next_zone_pgdat - helper magic for for_each_zone() per node
+ */
+struct zone *next_zone_pgdat(struct zone *zone, struct pglist_data *pgdat)
+{
+	if (!zone || !pgdat)
+		return NULL;
+	if (zone < pgdat->node_zones + MAX_NR_ZONES - 1)
+		return ++zone;
+	return NULL;
+}
+
 static inline int zref_in_nodemask(struct zoneref *zref, nodemask_t *nodes)
 {
 #ifdef CONFIG_NUMA