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mm: negative left shift count when PAGE_SHIFT > 20

PATCH New Jerry Zhou 1 participant 1 message Jul 20, 2013

Subsystems (2)
Memory management Page allocator
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Jerry Zhou

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PATCH 1/1 mm: negative left shift count when PAGE_SHIFT > 20

When PAGE_SHIFT > 20, the result of "20 - PAGE_SHIFT" is negative. The previous calculating here will generate an unexpected result. In addition, if PAGE_SIZE >= 1MB, The memory size of "numentries" was already integral multiple of 1MB.

Signed-off-by Jerry Zhou <[email protected]>
---
 mm/page_alloc.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)
mm/page_alloc.c +4 -3
index b100255..7c469c6 100644
@@ -5745,9 +5745,10 @@ void *__init alloc_large_system_hash(const char *tablename,
 	if (!numentries) {
 		/* round applicable memory size up to nearest megabyte */
 		numentries = nr_kernel_pages;
-		numentries += (1UL << (20 - PAGE_SHIFT)) - 1;
-		numentries >>= 20 - PAGE_SHIFT;
-		numentries <<= 20 - PAGE_SHIFT;
+
+		/* It isn't necessary when PAGE_SIZE >= 1MB */
+		if (PAGE_SHIFT < 20)
+			numentries = round_up(numentries, (1<<20)/PAGE_SIZE);
 
 		/* limit to 1 bucket per 2^scale bytes of low memory */
 		if (scale > PAGE_SHIFT)
Signature · 7 lines
1.8.1.5

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