linux-kernel - [PATCH] mm: negative left shift count when PAGE

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Date:	Sun, 21 Jul 2013 01:12:54 +0800
From:	Jerry Zhou <uulinux@...il.com>
To:	akpm@...ux-foundation.org
Cc:	zhuwei.lu@...hermind.com, tianfu.huang@...hermind.com,
	chunhua.zhou@...hermind.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Jerry Zhou <uulinux@...il.com>
Subject: [PATCH] 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 <uulinux@...il.com>
---
 mm/page_alloc.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index b100255..7c469c6 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -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)
-- 
1.8.1.5

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