On Thu, 2015-10-01 at 14:27 -0600, Ross Zwisler wrote:
> On Thu, Oct 01, 2015 at 05:46:33PM +1000, Dave Chinner wrote:
> > This reverts commit 46c043ede4711e8d598b9d63c5616c1fedb0605e.
> > ---
> > fs/dax.c | 36 ++++++++++++++++--------------------
> > mm/memory.c | 11 +++++++++--
> > 2 files changed, 25 insertions(+), 22 deletions(-)
> >
> > diff --git a/fs/dax.c b/fs/dax.c
> > index 7ae6df7..400fe95 100644
> > --- a/fs/dax.c
> > +++ b/fs/dax.c
> > @@ -569,26 +569,6 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
> > if (!buffer_size_valid(&bh) || bh.b_size < PMD_SIZE)
> > 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);
> > - wmb_pmem();
>
> The above two lines were updated to use the PMEM API with this commit:
>
> commit d77e92e270ed ("dax: update PMD fault handler with PMEM API")
>
> but they aren't updated in the reverted version here:
>
> > @@ -633,6 +620,15 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
> > if ((length < PMD_SIZE) || (pfn & PG_PMD_COLOUR))
> > 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);
> > + count_vm_event(PGMAJFAULT);
> > + mem_cgroup_count_vm_event(vma->vm_mm, PGMAJFAULT);
> > + result |= VM_FAULT_MAJOR;
> > + }
> > +
> > result |= vmf_insert_pfn_pmd(vma, address, pmd, pfn, write);
> > }
>
> This is the source of the follow-up sparse warning from the kbuild robot.
>
To that end Dave Hansen had also noticed that PTRS_PER_PMD should not be
used in this context. Here's an incremental cleanup:
8<---
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;
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