Le 19/09/2016 à 07:45, Aneesh Kumar K.V a écrit :

Christophe Leroy [off-list ref] writes:

quoted

Today there are two implementations of hugetlbpages which are managed
by exclusive #ifdefs:
* FSL_BOOKE: several directory entries points to the same single hugepage
* BOOK3S: one upper level directory entry points to a table of hugepages

In preparation of implementation of hugepage support on the 8xx, we
need a mix of the two above solutions, because the 8xx needs both cases
depending on the size of pages:
* In 4k page size mode, each PGD entry covers a 4M bytes area. It means
that 2 PGD entries will be necessary to cover an 8M hugepage while a
single PGD entry will cover 8x 512k hugepages.
* In 16 page size mode, each PGD entry covers a 64M bytes area. It means
that 8x 8M hugepages will be covered by one PGD entry and 64x 512k
hugepages will be covers by one PGD entry.

This patch:
* removes #ifdefs in favor of if/else based on the range sizes
* merges the two huge_pte_alloc() functions as they are pretty similar
* merges the two hugetlbpage_init() functions as they are pretty similar

Signed-off-by: Christophe Leroy <redacted>
---
v2: This part is new and results from a split of last patch of v1 serie in
two parts

 arch/powerpc/mm/hugetlbpage.c | 189 +++++++++++++++++-------------------------
 1 file changed, 77 insertions(+), 112 deletions(-)

diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c
index 8a512b1..2119f00 100644
--- a/arch/powerpc/mm/hugetlbpage.c
+++ b/arch/powerpc/mm/hugetlbpage.c

@@ -64,14 +64,16 @@ static int __hugepte_alloc(struct mm_struct *mm, hugepd_t *hpdp,
 {
 	struct kmem_cache *cachep;
 	pte_t *new;
-
-#ifdef CONFIG_PPC_FSL_BOOK3E
 	int i;
-	int num_hugepd = 1 << (pshift - pdshift);
-	cachep = hugepte_cache;
-#else
-	cachep = PGT_CACHE(pdshift - pshift);
-#endif
+	int num_hugepd;
+
+	if (pshift >= pdshift) {
+		cachep = hugepte_cache;
+		num_hugepd = 1 << (pshift - pdshift);
+	} else {
+		cachep = PGT_CACHE(pdshift - pshift);
+		num_hugepd = 1;
+	}

Is there a way to hint likely/unlikely branch based on the page size
selected at build time ?

Is that really worth it, won't it be negligeable compared to  other 
actions in that function (like for instance kmem_cache_zalloc()) ?
Can't we just trust GCC on that one ?

Christophe