On Mon, Nov 26, 2018 at 08:03:55AM +0100, Christophe LEROY wrote:
>
>
> Le 25/11/2018 à 22:44, Mike Rapoport a écrit :
> >There are several early memory allocations in arch/ code that use
> >memblock_phys_alloc() to allocate memory, convert the returned physical
> >address to the virtual address and then set the allocated memory to zero.
> >
> >Exactly the same behaviour can be achieved simply by calling
> >memblock_alloc(): it allocates the memory in the same way as
> >memblock_phys_alloc(), then it performs the phys_to_virt() conversion and
> >clears the allocated memory.
> >
> >Replace the longer sequence with a simpler call to memblock_alloc().
> >
> >Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxx>
> >---
> > arch/arm/mm/mmu.c | 4 +---
> > arch/c6x/mm/dma-coherent.c | 9 ++-------
> > arch/nds32/mm/init.c | 12 ++++--------
> > arch/powerpc/kernel/setup-common.c | 4 ++--
> > arch/powerpc/mm/pgtable_32.c | 4 +---
> > arch/powerpc/mm/ppc_mmu_32.c | 3 +--
> > arch/powerpc/platforms/powernv/opal.c | 3 +--
> > arch/sparc/kernel/prom_64.c | 7 ++-----
> > arch/sparc/mm/init_64.c | 9 +++------
> > arch/unicore32/mm/mmu.c | 4 +---
> > 10 files changed, 18 insertions(+), 41 deletions(-)
> >
> [...]
>
> >diff --git a/arch/powerpc/mm/pgtable_32.c b/arch/powerpc/mm/pgtable_32.c
> >index bda3c6f..9931e68 100644
> >--- a/arch/powerpc/mm/pgtable_32.c
> >+++ b/arch/powerpc/mm/pgtable_32.c
> >@@ -50,9 +50,7 @@ __ref pte_t *pte_alloc_one_kernel(struct mm_struct *mm, unsigned long address)
> > if (slab_is_available()) {
> > pte = (pte_t *)__get_free_page(GFP_KERNEL|__GFP_ZERO);
> > } else {
> >- pte = __va(memblock_phys_alloc(PAGE_SIZE, PAGE_SIZE));
> >- if (pte)
> >- clear_page(pte);
> >+ pte = memblock_alloc(PAGE_SIZE, PAGE_SIZE);
>
> memblock_alloc() uses memset to zeroize the block.
>
> clear_page() is more performant than memset().
As far as I can tell, the majority of the page table pages will be anyway
allocated with __get_free_page() so I think the performance loss here will
negligible.
> Christophe
>
> [...]
>
--
Sincerely yours,
Mike.
