Messages in this thread | | | Subject | Re: [PATCH v2 2/3] powerpc: get hugetlbpage handling more generic | From | Christophe Leroy <> | Date | Wed, 21 Sep 2016 08:13:56 +0200 |
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Le 19/09/2016 à 07:45, Aneesh Kumar K.V a écrit : > Christophe Leroy <christophe.leroy@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.leroy@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 *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
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