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>

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c2b59db..116bab1 100644 (file)
--- 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)