mm/sparse: clarify pgdat_to_phys

PATCH Applied Miles Chen 3 participants 3 messages Jul 23, 2021 – Jul 24, 2021

Subsystems (3)

Memory management Arm MediaTek MM core

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Miles Chen

author

2021-07-23 12:34 UTC #0 lore raw

PATCH v3 1/1 mm/sparse: clarify pgdat_to_phys

Clarify pgdat_to_phys() by testing if
pgdat == &contig_page_data when CONFIG_NUMA=n.

We only expect contig_page_data in such case, so we use &contig_page_data directly instead of pgdat.

No functional change intended when CONFIG_BUG_VM=n.

Comment from Mark [1]:
"
... and I reckon it'd be clearer and more robust to define pgdat_to_phys() in the same ifdefs as contig_page_data so that these, stay in-sync. e.g. have:

| #ifdef CONFIG_NUMA
| #define pgdat_to_phys(x)	virt_to_phys(x)
| #else /* CONFIG_NUMA */
|
| extern struct pglist_data contig_page_data;
| ...
| #define pgdat_to_phys(x)	__pa_symbol(&contig_page_data)
|
| #endif /* CONIFIG_NUMA */

[1] https://lore.kernel.org/linux-arm-kernel/[email protected]/

Cc Mike Rapoport <[email protected]>

Cc Mark Rutland <[email protected]>

Cc David Hildenbrand <[email protected]>

Signed-off-by Miles Chen <[email protected]>

Change since v1:
Thanks for Mike's comment, check if pgdat == &contig_page_data, so it is clearer that we only expect contig_page_data when CONFIG_NUMA=n.

Change since v2:
use VM_BUG_ON() to avoid runtime checking when CONFIG_BUG_VM=n

---
 mm/sparse.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

mm/sparse.c +2 -1

index 6326cdf36c4f..d13d831f88a5 100644
@@ -348,7 +348,8 @@ size_t mem_section_usage_size(void)
 static inline phys_addr_t pgdat_to_phys(struct pglist_data *pgdat)
 {
 #ifndef CONFIG_NUMA
-	return __pa_symbol(pgdat);
+	VM_BUG_ON(pgdat != &contig_page_data);
+	return __pa_symbol(&contig_page_data);
 #else
 	return __pa(pgdat);
 #endif

Signature · 1 line

2.18.0

David Hildenbrand

Reviewed-by on v3 1/1

2021-07-23 12:54 UTC #1 lore raw

Quoted 51 lines · Miles Chen

Clarify pgdat_to_phys() by testing if
pgdat == &contig_page_data when CONFIG_NUMA=n.
We only expect contig_page_data in such case, so we use &contig_page_data directly instead of pgdat.
No functional change intended when CONFIG_BUG_VM=n.
Comment from Mark [1]:
"
... and I reckon it'd be clearer and more robust to define pgdat_to_phys() in the same ifdefs as contig_page_data so that these, stay in-sync. e.g. have:
| #ifdef CONFIG_NUMA
| #define pgdat_to_phys(x)	virt_to_phys(x)
| #else /* CONFIG_NUMA */
|
| extern struct pglist_data contig_page_data;
| ...
| #define pgdat_to_phys(x)	__pa_symbol(&contig_page_data)
|
| #endif /* CONIFIG_NUMA */
"
[1] https://lore.kernel.org/linux-arm-kernel/[email protected]/
Cc Mike Rapoport <[email protected]>
Cc Mark Rutland <[email protected]>
Cc David Hildenbrand <[email protected]>
Signed-off-by Miles Chen <[email protected]>
--
Change since v1:
Thanks for Mike's comment, check if pgdat == &contig_page_data, so it is clearer that we only expect contig_page_data when CONFIG_NUMA=n.
Change since v2:
use VM_BUG_ON() to avoid runtime checking when CONFIG_BUG_VM=n
---
  mm/sparse.c | 3 ++-
  1 file changed, 2 insertions(+), 1 deletion(-)
mm/sparse.c +0 -0
index 6326cdf36c4f..d13d831f88a5 100644

mm/sparse.c size_t mem_section_usage_size(void) · line 355

Quoted 9 lines

mm/sparse.c +2 -1

@@ -348,7 +348,8 @@ size_t mem_section_usage_size(void)
  static inline phys_addr_t pgdat_to_phys(struct pglist_data *pgdat)
  {
  #ifndef CONFIG_NUMA
-	return __pa_symbol(pgdat);
+	VM_BUG_ON(pgdat != &contig_page_data);
+	return __pa_symbol(&contig_page_data);
  #else
  	return __pa(pgdat);
  #endif

Reviewed-by David Hildenbrand <[email protected]>

Signature · 3 lines

Thanks,

David / dhildenb

Mike Rapoport

reviewer Acked-by on v3 1/1

2021-07-24 07:47 UTC #2 lore raw

In reply to Miles Chen

Quoted 23 lines · Miles Chen

Clarify pgdat_to_phys() by testing if
pgdat == &contig_page_data when CONFIG_NUMA=n.
We only expect contig_page_data in such case, so we use &contig_page_data directly instead of pgdat.
No functional change intended when CONFIG_BUG_VM=n.
Comment from Mark [1]:
"
... and I reckon it'd be clearer and more robust to define pgdat_to_phys() in the same ifdefs as contig_page_data so that these, stay in-sync. e.g. have:
| #ifdef CONFIG_NUMA
| #define pgdat_to_phys(x)	virt_to_phys(x)
| #else /* CONFIG_NUMA */
|
| extern struct pglist_data contig_page_data;
| ...
| #define pgdat_to_phys(x)	__pa_symbol(&contig_page_data)
|
| #endif /* CONIFIG_NUMA */

Quoted 8 lines

"
[1] https://lore.kernel.org/linux-arm-kernel/[email protected]/
Cc Mike Rapoport <[email protected]>
Cc Mark Rutland <[email protected]>
Cc David Hildenbrand <[email protected]>
Signed-off-by Miles Chen <[email protected]>

Acked-by Mike Rapoport <[email protected]>

Quoted 31 lines

--
Change since v1:
Thanks for Mike's comment, check if pgdat == &contig_page_data, so it is clearer that we only expect contig_page_data when CONFIG_NUMA=n.
Change since v2:
use VM_BUG_ON() to avoid runtime checking when CONFIG_BUG_VM=n
---
 mm/sparse.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
mm/sparse.c +2 -1
index 6326cdf36c4f..d13d831f88a5 100644
@@ -348,7 +348,8 @@ size_t mem_section_usage_size(void)
 static inline phys_addr_t pgdat_to_phys(struct pglist_data *pgdat)
 {
 #ifndef CONFIG_NUMA
-	return __pa_symbol(pgdat);
+	VM_BUG_ON(pgdat != &contig_page_data);
+	return __pa_symbol(&contig_page_data);
 #else
 	return __pa(pgdat);
 #endif
Signature · 1 line
2.18.0

Signature · 2 lines

Sincerely yours,
Mike.