Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759264Ab3GRQ4u (ORCPT ); Thu, 18 Jul 2013 12:56:50 -0400 Received: from mail-pd0-f178.google.com ([209.85.192.178]:53365 "EHLO mail-pd0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754625Ab3GRQ4t (ORCPT ); Thu, 18 Jul 2013 12:56:49 -0400 From: Jerry To: akpm@linux-foundation.org Cc: zhuwei.lu@archermind.com, tianfu.huang@archermind.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Jerry Subject: [PATCH] mm: negative left shift count when PAGE_SHIFT > 20 Date: Fri, 19 Jul 2013 00:56:12 +0800 Message-Id: <1374166572-7988-1-git-send-email-uulinux@gmail.com> X-Mailer: git-send-email 1.8.1.5 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1300 Lines: 37 When PAGE_SHIFT > 20, the result of "20 - PAGE_SHIFT" is negative. The calculating here will generate an unexpected result. In addition, if PAGE_SHIFT > 20, The memory size represented by numentries was already integral multiple of 1MB. Signed-off-by: Jerry --- mm/page_alloc.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/mm/page_alloc.c b/mm/page_alloc.c index b100255..cd41797 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -5745,9 +5745,11 @@ 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; + if (20 > PAGE_SHIFT) { + numentries += (1UL << (20 - PAGE_SHIFT)) - 1; + numentries >>= 20 - PAGE_SHIFT; + numentries <<= 20 - PAGE_SHIFT; + } /* limit to 1 bucket per 2^scale bytes of low memory */ if (scale > PAGE_SHIFT) -- 1.8.1.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/