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Date: Fri, 14 Mar 2014 17:03:19 -0600
From: Toshi Kani <toshi.kani@...com>
To: willy@...ux.intel.com, kirill.shutemov@...ux.intel.com,
david@...morbit.com, linux-fsdevel@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
Toshi Kani <toshi.kani@...com>
Subject: [RFC PATCH] Support map_pages() for DAX
DAX provides direct access to NVDIMM and bypasses the page caches.
Newly introduced map_pages() callback reduces page faults by adding
mappings around a faulted page, which is not supported for DAX.
This patch implements map_pages() callback for DAX. It reduces a
number of page faults and increases read performance of DAX as shown
below. The values in parenthesis are relative to the base DAX results.
iozone results of mmap read/re-read tests [KB/sec]
64KB: read: 3,560,777 (x1.6) re-read: 9,086,412 (x1.8) pfault: 121 (-20%)
128MB: read: 4,374,906 (x1.7) re-read: 6,137,189 (x2.4) pfault: 8,312 (-87%)
Signed-off-by: Toshi Kani <toshi.kani@...com>
----
Applies on top of DAX patchset [1] and fault-around patchset [2].
[1] https://lkml.org/lkml/2014/2/25/460
[2] https://lkml.org/lkml/2014/2/27/546
---
fs/dax.c | 68 ++++++++++++++++++++++++++++++++++++++++++++++++++++
fs/ext4/file.c | 6 +++++
include/linux/fs.h | 5 ++++
3 files changed, 79 insertions(+)
diff --git a/fs/dax.c b/fs/dax.c
index c8dfab0..bc54705 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -476,3 +476,71 @@ int dax_zero_page_range(struct inode *inode, loff_t from, unsigned length,
return 0;
}
EXPORT_SYMBOL_GPL(dax_zero_page_range);
+
+static void dax_set_pte(struct vm_area_struct *vma, unsigned long addr,
+ unsigned long pfn, pte_t *pte)
+{
+ pte_t entry;
+
+ if (addr < vma->vm_start || addr >= vma->vm_end)
+ return;
+
+ if (!pte_none(*pte))
+ return;
+
+ entry = pte_mkspecial(pfn_pte(pfn, vma->vm_page_prot));
+ set_pte_at(vma->vm_mm, addr, pte, entry);
+ update_mmu_cache(vma, addr, pte);
+}
+
+void dax_map_pages(struct vm_area_struct *vma, struct vm_fault *vmf,
+ get_block_t get_block)
+{
+ struct file *file = vma->vm_file;
+ struct inode *inode = file_inode(file);
+ struct buffer_head bh;
+ struct address_space *mapping = file->f_mapping;
+ unsigned long vaddr = (unsigned long)vmf->virtual_address;
+ pgoff_t pgoff = vmf->pgoff;
+ sector_t block;
+ pgoff_t size;
+ unsigned long pfn;
+ pte_t *pte = vmf->pte;
+ int error;
+
+ while (pgoff < vmf->max_pgoff) {
+ size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
+ if (pgoff >= size)
+ return;
+
+ memset(&bh, 0, sizeof(bh));
+ block = (sector_t)pgoff << (PAGE_SHIFT - inode->i_blkbits);
+ bh.b_size = PAGE_SIZE;
+ error = get_block(inode, block, &bh, 0);
+ if (error || bh.b_size < PAGE_SIZE)
+ goto next;
+
+ if (!buffer_mapped(&bh) || buffer_unwritten(&bh) ||
+ buffer_new(&bh))
+ goto next;
+
+ /* Recheck i_size under i_mmap_mutex */
+ mutex_lock(&mapping->i_mmap_mutex);
+ size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
+ if (unlikely(pgoff >= size)) {
+ mutex_unlock(&mapping->i_mmap_mutex);
+ return;
+ }
+
+ error = dax_get_pfn(inode, &bh, &pfn);
+ if (error > 0)
+ dax_set_pte(vma, vaddr, pfn, pte);
+
+ mutex_unlock(&mapping->i_mmap_mutex);
+next:
+ vaddr += PAGE_SIZE;
+ pgoff++;
+ pte++;
+ }
+}
+EXPORT_SYMBOL_GPL(dax_map_pages);
diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index eb19383..15965ea 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -205,6 +205,11 @@ static int ext4_dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
/* Is this the right get_block? */
}
+static void ext4_dax_map_pages(struct vm_area_struct *vma, struct vm_fault *vmf)
+{
+ return dax_map_pages(vma, vmf, ext4_get_block);
+}
+
static int ext4_dax_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
{
return dax_mkwrite(vma, vmf, ext4_get_block);
@@ -212,6 +217,7 @@ static int ext4_dax_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
static const struct vm_operations_struct ext4_dax_vm_ops = {
.fault = ext4_dax_fault,
+ .map_pages = ext4_dax_map_pages,
.page_mkwrite = ext4_dax_mkwrite,
.remap_pages = generic_file_remap_pages,
};
diff --git a/include/linux/fs.h b/include/linux/fs.h
index d0381ab..3bd1042 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2527,6 +2527,7 @@ ssize_t dax_do_io(int rw, struct kiocb *, struct inode *, const struct iovec *,
loff_t, unsigned segs, get_block_t, dio_iodone_t, int flags);
int dax_fault(struct vm_area_struct *, struct vm_fault *, get_block_t);
int dax_mkwrite(struct vm_area_struct *, struct vm_fault *, get_block_t);
+void dax_map_pages(struct vm_area_struct *, struct vm_fault *, get_block_t);
#else
static inline int dax_clear_blocks(struct inode *i, sector_t blk, long sz)
{
@@ -2545,6 +2546,10 @@ static inline ssize_t dax_do_io(int rw, struct kiocb *iocb, struct inode *inode,
{
return -ENOTTY;
}
+static inline void dax_map_pages(struct vm_area_struct *vma,
+ struct vm_fault *vmf, get_block_t get_block)
+{
+}
#endif
/* Can't be a function because PAGE_CACHE_SIZE is defined in pagemap.h */
--
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