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

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Date:   Tue, 13 Sep 2016 17:26:05 +0800
From:   Rui Teng <rui.teng@...ux.vnet.ibm.com>
To:     linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:     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, Rui Teng <rui.teng@...ux.vnet.ibm.com>
Subject: [RFC] mm: Change the data type of huge page size from unsigned long to u64

The huge page size could be 16G(0x400000000) on ppc64 architecture, and it will
cause an overflow on unsigned long data type(0xFFFFFFFF).

For example, huge_page_size() will return 0, if the PAGE_SIZE is 65536 and
h->order is 18, which is the result on ppc64 with 16G huge page enabled.

I think it needs to change the data type from unsigned long to u64. But it will
cause a lot of functions and data structures changed. Any comments and
suggestions?

Thanks!

Signed-off-by: Rui Teng <rui.teng@...ux.vnet.ibm.com>
---
 include/linux/hugetlb.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index c26d463..efbe5cf 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -374,9 +374,9 @@ static inline struct hstate *hstate_vma(struct vm_area_struct *vma)
 	return hstate_file(vma->vm_file);
 }
 
-static inline unsigned long huge_page_size(struct hstate *h)
+static inline u64 huge_page_size(struct hstate *h)
 {
-	return (unsigned long)PAGE_SIZE << h->order;
+	return (u64)PAGE_SIZE << h->order;
 }
 
 extern unsigned long vma_kernel_pagesize(struct vm_area_struct *vma);
-- 
2.7.4