[PATCH 6/6] arm64: mm: Enable RCU fast_gup
mark.rutland at arm.com
Wed Jun 25 09:50:03 PDT 2014
On Wed, Jun 25, 2014 at 04:40:24PM +0100, Steve Capper wrote:
> Activate the RCU fast_gup for ARM64. We also need to force THP splits
> to broadcast an IPI s.t. we block in the fast_gup page walker. As THP
> splits are comparatively rare, this should not lead to a noticeable
> performance degradation.
> Some pre-requisite functions pud_write and pud_page are also added.
> Signed-off-by: Steve Capper <steve.capper at linaro.org>
> arch/arm64/Kconfig | 3 +++
> arch/arm64/include/asm/pgtable.h | 11 ++++++++++-
> arch/arm64/mm/flush.c | 19 +++++++++++++++++++
> 3 files changed, 32 insertions(+), 1 deletion(-)
> diff --git a/arch/arm64/mm/flush.c b/arch/arm64/mm/flush.c
> index e4193e3..ddf96c1 100644
> --- a/arch/arm64/mm/flush.c
> +++ b/arch/arm64/mm/flush.c
> @@ -103,3 +103,22 @@ EXPORT_SYMBOL(flush_dcache_page);
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +#ifdef CONFIG_HAVE_RCU_TABLE_FREE
> +static void thp_splitting_flush_sync(void *arg)
> +void pmdp_splitting_flush(struct vm_area_struct *vma, unsigned long address,
> + pmd_t *pmdp)
> + pmd_t pmd = pmd_mksplitting(*pmdp);
> + VM_BUG_ON(address & ~PMD_MASK);
> + set_pmd_at(vma->vm_mm, address, pmdp, pmd);
> + /* dummy IPI to serialise against fast_gup */
> + smp_call_function(thp_splitting_flush_sync, NULL, 1);
Is there some reason we can't use kick_all_cpus_sync()?
>From a glance it seems that powerpc does just that.
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