mm: fix 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@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 4 insertions, 3 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c2b59dbda196..116bab1c2cf5 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)