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mm/vmalloc: interchage the implementation of vmalloc_to_{pfn,page}

PATCH In review Jianyu Zhan 2 participants 2 messages Nov 28, 2013

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Memory management vmalloc
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Jianyu Zhan

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#0 lore raw

PATCH 1/1 mm/vmalloc: interchage the implementation of vmalloc_to_{pfn,page}

Currently we are implementing vmalloc_to_pfn() as a wrapper of vmalloc_to_page(), which is implemented as follow:

1. walks the page talbes to generates the corresponding pfn,
2. then wraps the pfn to struct page,
3. returns it.

And vmalloc_to_pfn() re-wraps the vmalloc_to_page() to get the pfn.

This seems too circuitous, so this patch reverses the way:
implementing the vmalloc_to_page() as a wrapper of vmalloc_to_pfn(). This makes vmalloc_to_pfn() and vmalloc_to_page() slightly effective.

No functional change.

Signed-off-by Jianyu Zhan <[email protected]>

---
mm/vmalloc.c | 20 ++++++++++----------

 1 file changed, 10 insertions(+), 10 deletions(-)
mm/vmalloc.c +10 -10
index 0fdf968..a335e21 100644
@@ -220,12 +220,12 @@ int is_vmalloc_or_module_addr(const void *x)
 }
 
 /*
- * Walk a vmap address to the struct page it maps.
+ * Walk a vmap address to the physical pfn it maps to.
  */
-struct page *vmalloc_to_page(const void *vmalloc_addr)
+unsigned long vmalloc_to_pfn(const void *vmalloc_addr)
 {
 	unsigned long addr = (unsigned long) vmalloc_addr;
-	struct page *page = NULL;
+	unsigned long pfn;
 	pgd_t *pgd = pgd_offset_k(addr);
 
 	/*

@@ -244,23 +244,23 @@ struct page *vmalloc_to_page(const void *vmalloc_addr)
 				ptep = pte_offset_map(pmd, addr);
 				pte = *ptep;
 				if (pte_present(pte))
-					page = pte_page(pte);
+					pfn = pte_page(pte);
 				pte_unmap(ptep);
 			}
 		}
 	}
-	return page;
+	return pfn;
 }
-EXPORT_SYMBOL(vmalloc_to_page);
+EXPORT_SYMBOL(vmalloc_to_pfn);
 
 /*
- * Map a vmalloc()-space virtual address to the physical page frame number.
+ * Map a vmalloc()-space virtual address to the struct page.
  */
-unsigned long vmalloc_to_pfn(const void *vmalloc_addr)
+struct page *vmalloc_to_page(const void *vmalloc_addr)
 {
-	return page_to_pfn(vmalloc_to_page(vmalloc_addr));
+	return pfn_to_page(vmalloc_to_pfn(vmalloc_addr));
 }
-EXPORT_SYMBOL(vmalloc_to_pfn);
+EXPORT_SYMBOL(vmalloc_to_page);
 
 
 /*** Global kva allocator ***/

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#1 lore raw
Quoted 7 lines · Jianyu Zhan

Currently we are implementing vmalloc_to_pfn() as a wrapper of vmalloc_to_page(), which is implemented as follow:

1. walks the page talbes to generates the corresponding pfn,
2. then wraps the pfn to struct page,
3. returns it.

Quoted 5 lines

And vmalloc_to_pfn() re-wraps the vmalloc_to_page() to get the pfn.

This seems too circuitous, so this patch reverses the way:
implementing the vmalloc_to_page() as a wrapper of vmalloc_to_pfn(). This makes vmalloc_to_pfn() and vmalloc_to_page() slightly effective.

Any numbers for efficiency?

Quoted 16 lines

No functional change.

Signed-off-by Jianyu Zhan <[email protected]>

---
mm/vmalloc.c | 20 ++++++++++----------

 1 file changed, 10 insertions(+), 10 deletions(-)
mm/vmalloc.c +0 -0
index 0fdf968..a335e21 100644
@@ -220,12 +220,12 @@ int is_vmalloc_or_module_addr(const void *x)
 }

mm/vmalloc.c int is_vmalloc_or_module_addr(const void *x) · line 228

Quoted 10 lines
mm/vmalloc.c +3 -3
 /*
- * Walk a vmap address to the struct page it maps.
+ * Walk a vmap address to the physical pfn it maps to.
  */
-struct page *vmalloc_to_page(const void *vmalloc_addr)
+unsigned long vmalloc_to_pfn(const void *vmalloc_addr)
 {
 	unsigned long addr = (unsigned long) vmalloc_addr;
-	struct page *page = NULL;
+	unsigned long pfn;

uninitialized pfn will lead to a bug.

mm/vmalloc.c struct page *vmalloc_to_page(const void *vmalloc_addr) · line 247

Quoted 9 lines
mm/vmalloc.c +1 -1
 	pgd_t *pgd = pgd_offset_k(addr);
 
 	/*

@@ -244,23 +244,23 @@ struct page *vmalloc_to_page(const void *vmalloc_addr)
 				ptep = pte_offset_map(pmd, addr);
 				pte = *ptep;
 				if (pte_present(pte))
-					page = pte_page(pte);
+					pfn = pte_page(pte);

page_to_pfn is missed here.

Have you ever tested there is no functional changes?

Vladimir

Quoted 27 lines
mm/vmalloc.c +6 -7
 				pte_unmap(ptep);
 			}
 		}
 	}
-	return page;
+	return pfn;
 }
-EXPORT_SYMBOL(vmalloc_to_page);
+EXPORT_SYMBOL(vmalloc_to_pfn);
 
 /*
- * Map a vmalloc()-space virtual address to the physical page frame number.
+ * Map a vmalloc()-space virtual address to the struct page.
  */
-unsigned long vmalloc_to_pfn(const void *vmalloc_addr)
+struct page *vmalloc_to_page(const void *vmalloc_addr)
 {
-	return page_to_pfn(vmalloc_to_page(vmalloc_addr));
+	return pfn_to_page(vmalloc_to_pfn(vmalloc_addr));
 }
-EXPORT_SYMBOL(vmalloc_to_pfn);
+EXPORT_SYMBOL(vmalloc_to_page);
 
 
 /*** Global kva allocator ***/
 
--
Quoted 4 lines

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