On Thu, Oct 01, 2015 at 10:14:22PM +0000, Williams, Dan J wrote:
> Subject: pmem, dax: clean up clear_pmem()
>
> From: Dan Williams <dan.j.williams@xxxxxxxxx>
>
> Both, __dax_pmd_fault, and clear_pmem() were taking special steps to
> clear memory a page at a time to take advantage of non-temporal
> clear_page() implementations. However, x86_64 does not use
> non-temporal instructions for clear_page(), and arch_clear_pmem() was
> always incurring the cost of __arch_wb_cache_pmem().
>
> Clean up the assumption that doing clear_pmem() a page at a time is more
> performant.
>
> Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
> Reported-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> ---
> arch/x86/include/asm/pmem.h | 7 +------
> fs/dax.c | 4 +---
> 2 files changed, 2 insertions(+), 9 deletions(-)
>
> diff --git a/arch/x86/include/asm/pmem.h b/arch/x86/include/asm/pmem.h
> index d8ce3ec816ab..1544fabcd7f9 100644
> --- a/arch/x86/include/asm/pmem.h
> +++ b/arch/x86/include/asm/pmem.h
> @@ -132,12 +132,7 @@ static inline void arch_clear_pmem(void __pmem *addr, size_t size)
> {
> void *vaddr = (void __force *)addr;
>
> - /* TODO: implement the zeroing via non-temporal writes */
> - if (size == PAGE_SIZE && ((unsigned long)vaddr & ~PAGE_MASK) == 0)
> - clear_page(vaddr);
> - else
> - memset(vaddr, 0, size);
> -
> + memset(vaddr, 0, size);
> __arch_wb_cache_pmem(vaddr, size);
> }
>
> diff --git a/fs/dax.c b/fs/dax.c
> index b36d6d2e7f87..3faff9227135 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -625,9 +625,7 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
> goto fallback;
>
> if (buffer_unwritten(&bh) || buffer_new(&bh)) {
> - int i;
> - for (i = 0; i < PTRS_PER_PMD; i++)
> - clear_page(kaddr + i * PAGE_SIZE);
> + clear_pmem(kaddr, HPAGE_SIZE);
> count_vm_event(PGMAJFAULT);
> mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
> result |= VM_FAULT_MAJOR;
>
This clear_pmem() needs a wmb_pmem() after it. I'll make a quick series with
the clean revert and this guy at the end and try and get them in v4.3 - sound
good?
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