Le 19/09/2016 à 07:45, Aneesh Kumar K.V a écrit :
Christophe Leroy <christophe.le...@c-s.fr> writes:

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 <christophe.le...@c-s.fr>
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 
        struct kmem_cache *cachep;
        pte_t *new;
        int i;
-       int num_hugepd = 1 << (pshift - pdshift);
-       cachep = hugepte_cache;
-       cachep = PGT_CACHE(pdshift - pshift);
+       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 ?


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