[PATCH 2/2] dax: Only fault once on mmap write access

[Boaz Harrosh <boaz@plexistor.com>]

In current code for any mmap-write access there are two page faults.
One that maps the pfn into the vma (vm_insert_mixed()), and a second
one that converts the read-only mapping to read-write (via pfn_mkwrite).

But since we already know that this is a write access we can map the
pfn read-write and save the extra fault.

Signed-off-by: Boaz Harrosh <boaz@plexistor.com>
---
 fs/dax.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/dax.c b/fs/dax.c
index a86d3cc..3fee696 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -289,6 +289,7 @@ static int dax_insert_mapping(struct inode *inode, struct buffer_head *bh,
 	sector_t sector = bh->b_blocknr << (inode->i_blkbits - 9);
 	unsigned long vaddr = (unsigned long)vmf->virtual_address;
 	void __pmem *addr;
+	pgprot_t prot = vma->vm_page_prot;
 	unsigned long pfn;
 	pgoff_t size;
 	int error;
@@ -321,7 +322,10 @@ static int dax_insert_mapping(struct inode *inode, struct buffer_head *bh,
 		wmb_pmem();
 	}
 
-	error = vm_insert_mixed(vma, vaddr, pfn);
+	if (vmf->flags & FAULT_FLAG_WRITE)
+		prot = pgprot_modify(prot, PAGE_SHARED);
+
+	error = vm_insert_mixed_prot(vma, vaddr, pfn, prot);
 
  out:
 	i_mmap_unlock_read(mapping);
-- 
1.9.3


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