memory hotplug: update the variables after memory removed

Commit ea0854170c95245a258b386c7a9314399c949fe0 added a fuction

update_end_of_memory_vars() to update high_memory, max_pfn and max_low_pfn.

I modified the function according to Dave Hansen and David Rientjes's suggestions.
And call it in arch_remove_memory() to update these variables too.

Change v1->v2:
- according to Dave Hansen and David Rientjes's suggestions modified update_end_of_memory_vars().

Signed-off-by Zhang Zhen <[email protected]>

---
 arch/x86/mm/init_64.c | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

arch/x86/mm/init_64.c +0 -0

index df1a992..fd7bd6b 100644

arch/x86/mm/init_64.c +8 -8

 {
-	unsigned long end_pfn = PFN_UP(start + size);
-
-	if (end_pfn > max_pfn) {
-		max_pfn = end_pfn;
-		max_low_pfn = end_pfn;
-		high_memory = (void *)__va(max_pfn * PAGE_SIZE - 1) + 1;
-	}
+	max_pfn = end_pfn;
+	max_low_pfn = end_pfn;
+	high_memory = (void *)__va(max_pfn * PAGE_SIZE - 1) + 1;
 }
 
 /*

@@ -694,6 +690,7 @@ int arch_add_memory(int nid, u64 start, u64 size)
 	struct zone *zone = pgdat->node_zones + ZONE_NORMAL;
 	unsigned long start_pfn = start >> PAGE_SHIFT;
 	unsigned long nr_pages = size >> PAGE_SHIFT;
+	unsigned long end_pfn;
 	int ret;
 
 	init_memory_mapping(start, start + size);

@@ -702,7 +699,9 @@ int arch_add_memory(int nid, u64 start, u64 size)
 	WARN_ON_ONCE(ret);
 
 	/* update max_pfn, max_low_pfn and high_memory */
-	update_end_of_memory_vars(start, size);
+	end_pfn = start_pfn + nr_pages;
+	if (end_pfn > max_pfn)
+		update_end_of_memory_vars(end_pfn);
 
 	return ret;
 }

@@ -1018,6 +1017,7 @@ int __ref arch_remove_memory(u64 start, u64 size)
 	unsigned long start_pfn = start >> PAGE_SHIFT;
 	unsigned long nr_pages = size >> PAGE_SHIFT;
 	struct zone *zone;
+	unsigned long end_pfn;
 	int ret;
 
 	zone = page_zone(pfn_to_page(start_pfn));

Quoted 1 line · Zhang Zhen

Commit ea0854170c95245a258b386c7a9314399c949fe0 added a fuction

This would normally be written as

Commit ea0854170c95 ("memory hotplug: fix a bug on /dev/mem for 64-bit kernels") ...

Quoted 7 lines

update_end_of_memory_vars() to update high_memory, max_pfn and max_low_pfn.

I modified the function according to Dave Hansen and David Rientjes's suggestions.
And call it in arch_remove_memory() to update these variables too.

When the x86 maintainers merge this patch, they'll need to make a judgment call on how urgent the fix is and that will guide them in whether they want it backported to stable kernels as well. It would be useful to provide the rationale for the change; in other words, why is the change needed and what breaks if we don't have it?

Quoted 5 lines

Change v1->v2:
- according to Dave Hansen and David Rientjes's suggestions modified update_end_of_memory_vars().

Signed-off-by Zhang Zhen <[email protected]>

Acked-by David Rientjes <[email protected]>

You'll want to email all the x86 maintainers who would handle this patch, check the output of scripts/get_maintainer.pl when run on this diff.

Quoted 5 lines

---
 arch/x86/mm/init_64.c | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

arch/x86/mm/init_64.c void __init paging_init(void) · line 676

Quoted 10 lines

arch/x86/mm/init_64.c +1 -1

index df1a992..fd7bd6b 100644
@@ -673,15 +673,11 @@ void __init paging_init(void)
  * After memory hotplug the variables max_pfn, max_low_pfn and high_memory need
  * updating.
  */
-static void  update_end_of_memory_vars(u64 start, u64 size)
+static void  update_end_of_memory_vars(u64 end_pfn)

Extra space that can be removed here at the same time as a cleanup.

Quoted 45 lines

arch/x86/mm/init_64.c +8 -8

 {
-	unsigned long end_pfn = PFN_UP(start + size);
-
-	if (end_pfn > max_pfn) {
-		max_pfn = end_pfn;
-		max_low_pfn = end_pfn;
-		high_memory = (void *)__va(max_pfn * PAGE_SIZE - 1) + 1;
-	}
+	max_pfn = end_pfn;
+	max_low_pfn = end_pfn;
+	high_memory = (void *)__va(max_pfn * PAGE_SIZE - 1) + 1;
 }
 
 /*

@@ -694,6 +690,7 @@ int arch_add_memory(int nid, u64 start, u64 size)
 	struct zone *zone = pgdat->node_zones + ZONE_NORMAL;
 	unsigned long start_pfn = start >> PAGE_SHIFT;
 	unsigned long nr_pages = size >> PAGE_SHIFT;
+	unsigned long end_pfn;
 	int ret;
 
 	init_memory_mapping(start, start + size);

@@ -702,7 +699,9 @@ int arch_add_memory(int nid, u64 start, u64 size)
 	WARN_ON_ONCE(ret);
 
 	/* update max_pfn, max_low_pfn and high_memory */
-	update_end_of_memory_vars(start, size);
+	end_pfn = start_pfn + nr_pages;
+	if (end_pfn > max_pfn)
+		update_end_of_memory_vars(end_pfn);
 
 	return ret;
 }

@@ -1018,6 +1017,7 @@ int __ref arch_remove_memory(u64 start, u64 size)
 	unsigned long start_pfn = start >> PAGE_SHIFT;
 	unsigned long nr_pages = size >> PAGE_SHIFT;
 	struct zone *zone;
+	unsigned long end_pfn;
 	int ret;
 
 	zone = page_zone(pfn_to_page(start_pfn));

@@ -1025,6 +1025,11 @@ int __ref arch_remove_memory(u64 start, u64 size)
 	ret = __remove_pages(zone, start_pfn, nr_pages);
 	WARN_ON_ONCE(ret);
 

arch/x86/mm/init_64.c int __ref arch_remove_memory(u64 start, u64 size) · line 1031

Quoted 4 lines

arch/x86/mm/init_64.c +4 -0

+	/* update max_pfn, max_low_pfn and high_memory */
+	end_pfn = start_pfn + nr_pages;
+	if ((max_pfn >= start_pfn) && (max_pfn < end_pfn))
+		update_end_of_memory_vars(start_pfn);

Not sure if we really need the new variable here; if you choose to repropose this patch then you may want to consider just using start_pfn + nr_pages in the conditional.

arch/x86/mm/init_64.c int __ref arch_remove_memory(u64 start, u64 size) · line 1035

Quoted 5 lines

arch/x86/mm/init_64.c +1 -0

+
 	return ret;
 }
 #endif

.

Quoted 4 lines

Quoted 4 lines

arch/x86/mm/init_64.c +0 -0

index df1a992..fd7bd6b 100644

Quoted 9 lines

arch/x86/mm/init_64.c void __init paging_init(void) · line 676

Quoted 6 lines

arch/x86/mm/init_64.c +1 -1

@@ -673,15 +673,11 @@ void __init paging_init(void)
  * After memory hotplug the variables max_pfn, max_low_pfn and high_memory need
  * updating.
  */
-static void  update_end_of_memory_vars(u64 start, u64 size)
+static void  update_end_of_memory_vars(u64 end_pfn)

Extra space that can be removed here at the same time as a cleanup.

Sorry, where is the extra space here?

Quoted 13 lines · Zhang Zhen

Quoted 13 lines

arch/x86/mm/init_64.c void __init paging_init(void) · line 676

Quoted 10 lines

arch/x86/mm/init_64.c +1 -1

index df1a992..fd7bd6b 100644
@@ -673,15 +673,11 @@ void __init paging_init(void)
  * After memory hotplug the variables max_pfn, max_low_pfn and high_memory need
  * updating.
  */
-static void  update_end_of_memory_vars(u64 start, u64 size)
+static void  update_end_of_memory_vars(u64 end_pfn)

Extra space that can be removed here at the same time as a cleanup.

Quoted 2 lines

Sorry, where is the extra space here?

There are two spaces between the function identifier and the function type whereas there is traditionally only one. It existed before your patch, it would just be nice to clean it up since you're already touching the line.