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[PATCH v2 1/5] pmem, dax: clean up clear_pmem()

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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@linux.intel.com>
Reported-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 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 a86d3cc2b389..5dc33d788d50 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -623,9 +623,7 @@ 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_pmem(kaddr + i * PAGE_SIZE, PAGE_SIZE);
+			clear_pmem(kaddr, HPAGE_SIZE);
 			wmb_pmem();
 			count_vm_event(PGMAJFAULT);
 			mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);

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Thread

[PATCH v2 0/5] block, dax: updates for 4.4 Dan Williams <dan.j.williams@intel.com> - 2015-10-22 19:20 +0200
  [PATCH v2 5/5] block: enable dax for raw block devices Dan Williams <dan.j.williams@intel.com> - 2015-10-22 19:20 +0200
    Re: [PATCH v2 5/5] block: enable dax for raw block devices Jeff Moyer <jmoyer@redhat.com> - 2015-10-28 22:00 +0100
      Re: [PATCH v2 5/5] block: enable dax for raw block devices Dan Williams <dan.j.williams@intel.com> - 2015-10-29 08:20 +0100
  [PATCH v2 4/5] block: introduce bdev_file_inode() Dan Williams <dan.j.williams@intel.com> - 2015-10-22 19:20 +0200
    Re: [PATCH v2 4/5] block: introduce bdev_file_inode() Jan Kara <jack@suse.cz> - 2015-10-22 22:40 +0200
    Re: [PATCH v2 4/5] block: introduce bdev_file_inode() Jeff Moyer <jmoyer@redhat.com> - 2015-10-28 21:20 +0100
  [PATCH v2 3/5] block,  dax: fix lifetime of in-kernel dax mappings with dax_map_atomic() Dan Williams <dan.j.williams@intel.com> - 2015-10-22 19:20 +0200
    Re: [PATCH v2 3/5] block, dax: fix lifetime of in-kernel dax mappings with dax_map_atomic() Jeff Moyer <jmoyer@redhat.com> - 2015-10-28 21:20 +0100
  [PATCH v2 2/5] dax: increase granularity of dax_clear_blocks()  operations Dan Williams <dan.j.williams@intel.com> - 2015-10-22 19:20 +0200
    Re: [PATCH v2 2/5] dax: increase granularity of dax_clear_blocks() operations Jeff Moyer <jmoyer@redhat.com> - 2015-10-22 23:10 +0200
      Re: [PATCH v2 2/5] dax: increase granularity of dax_clear_blocks()  operations "Williams, Dan J" <dan.j.williams@intel.com> - 2015-10-23 01:00 +0200
        Re: [PATCH v2 2/5] dax: increase granularity of dax_clear_blocks() operations Jeff Moyer <jmoyer@redhat.com> - 2015-10-28 22:10 +0100
  [PATCH v2 1/5] pmem, dax: clean up clear_pmem() Dan Williams <dan.j.williams@intel.com> - 2015-10-22 19:20 +0200
    Re: [PATCH v2 1/5] pmem, dax: clean up clear_pmem() Jeff Moyer <jmoyer@redhat.com> - 2015-10-22 22:50 +0200
      Re: [PATCH v2 1/5] pmem, dax: clean up clear_pmem() Dan Williams <dan.j.williams@intel.com> - 2015-10-23 00:30 +0200
        Re: [PATCH v2 1/5] pmem, dax: clean up clear_pmem() Jeff Moyer <jmoyer@redhat.com> - 2015-10-28 22:10 +0100
    Re: [PATCH v2 1/5] pmem, dax: clean up clear_pmem() Ross Zwisler <ross.zwisler@linux.intel.com> - 2015-10-27 18:40 +0100

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