From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx192.postini.com [74.125.245.192]) by kanga.kvack.org (Postfix) with SMTP id 510B96B0031 for ; Thu, 18 Jul 2013 12:56:49 -0400 (EDT) Received: by mail-pb0-f46.google.com with SMTP id rq2so3384455pbb.5 for ; Thu, 18 Jul 2013 09:56:48 -0700 (PDT) From: 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> Sender: owner-linux-mm@kvack.org List-ID: To: akpm@linux-foundation.org Cc: zhuwei.lu@archermind.com, tianfu.huang@archermind.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Jerry 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, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org