linux-kernel - Re: [RFC] mm: Change the data type of huge page size from unsigned long to u64

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Date:   Tue, 13 Sep 2016 21:08:33 +0800
From:   Rui Teng <rui.teng@...ux.vnet.ibm.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        Chen Gang <chengang@...ndsoft.com.cn>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Aneesh Kumar K . V" <aneesh.kumar@...ux.vnet.ibm.com>,
        hejianet@...ux.vnet.ibm.com
Subject: Re: [RFC] mm: Change the data type of huge page size from unsigned
 long to u64

On 9/13/16 7:40 PM, Kirill A. Shutemov wrote:
> On Tue, Sep 13, 2016 at 07:21:07PM +0800, Rui Teng wrote:
>> On 9/13/16 5:32 PM, Kirill A. Shutemov wrote:
>>> On Tue, Sep 13, 2016 at 05:26:05PM +0800, Rui Teng wrote:
>>>> The huge page size could be 16G(0x400000000) on ppc64 architecture, and it will
>>>> cause an overflow on unsigned long data type(0xFFFFFFFF).
>>>
>>> Huh? ppc64 is 64-bit system and sizeof(void *) is equal to
>>> sizeof(unsigned long) on Linux (LP64 model).
>>>
>>> So where your 0xFFFFFFFF comes from?
>>>
>> The size of unsigned long data type is 4 bytes
>
> No, it's not.
>
Sorry, my fault!
I print the unsigned long with "%ul" instead of "%lu" and got the wrong
result. Sorry!