[PATCH] mm, proc: add workaround for old compilers

[Kirill A. Shutemov]

For THP=n, HPAGE_PMD_NR in smaps_account() expands to BUILD_BUG().
That's fine since this codepath is eliminated by modern compilers.

But older compilers have not that efficient dead code elimination.
It causes problem at least with gcc 4.1.2 on m68k.

Let's replace HPAGE_PMD_NR with 1 << compound_order(page).

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Reported-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
---
 fs/proc/task_mmu.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 65a1b6c69c11..71ffc91060f6 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -468,7 +468,7 @@ struct mem_size_stats {
 static void smaps_account(struct mem_size_stats *mss, struct page *page,
 		bool compound, bool young, bool dirty)
 {
-	int i, nr = compound ? HPAGE_PMD_NR : 1;
+	int i, nr = compound ? 1 << compound_order(page) : 1;
 	unsigned long size = nr * PAGE_SIZE;
 
 	if (PageAnon(page))
-- 
 Kirill A. Shutemov