This patchset aims to take care of this issue to make reflink and dedupe
work correctly (actually in read/write path, there still has some problems,
such as the page->mapping and page->index issue, in mmap path) in XFS under
fsdax mode.
It is based on Goldwyn's patchsets: "v4 Btrfs dax support" and the latest
iomap. I borrowed some patches related and made a few fix to make it
basically works fine.
For dax framework:
1. adapt to the latest change in iomap (two iomaps).
For XFS:
1. distinguish dax write/zero from normal write/zero.
2. remap extents after COW.
3. add file contents comparison function based on dax framework.
4. use xfs_break_layouts() instead of break_layout to support dax.
Goldwyn Rodrigues (3):
dax: replace mmap entry in case of CoW
fs: dedup file range to use a compare function
dax: memcpy before zeroing range
Shiyang Ruan (4):
dax: Introduce dax_copy_edges() for COW.
dax: copy data before write.
xfs: handle copy-on-write in fsdax write() path.
xfs: support dedupe for fsdax.
fs/btrfs/ioctl.c | 3 +-
fs/dax.c | 211 +++++++++++++++++++++++++++++++++++++----
fs/iomap/buffered-io.c | 8 +-
fs/ocfs2/file.c | 2 +-
fs/read_write.c | 11 ++-
fs/xfs/xfs_bmap_util.c | 6 +-
fs/xfs/xfs_file.c | 10 +-
fs/xfs/xfs_iomap.c | 3 +-
fs/xfs/xfs_iops.c | 11 ++-
fs/xfs/xfs_reflink.c | 79 ++++++++-------
include/linux/dax.h | 16 ++--
include/linux/fs.h | 9 +-
12 files changed, 291 insertions(+), 78 deletions(-)
--
2.23.0
From: Goldwyn Rodrigues <[email protected]>
We replace the existing entry to the newly allocated one
in case of CoW. Also, we mark the entry as PAGECACHE_TAG_TOWRITE
so writeback marks this entry as writeprotected. This
helps us snapshots so new write pagefaults after snapshots
trigger a CoW.
btrfs does not support hugepages so we don't handle PMD.
Signed-off-by: Goldwyn Rodrigues <[email protected]>
---
fs/dax.c | 40 ++++++++++++++++++++++++++++++----------
1 file changed, 30 insertions(+), 10 deletions(-)
diff --git a/fs/dax.c b/fs/dax.c
index 949a40cf1fe7..e6174c0c669a 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -705,6 +705,9 @@ static int copy_user_dax(struct block_device *bdev, struct dax_device *dax_dev,
return 0;
}
+#define DAX_IF_DIRTY (1ULL << 0)
+#define DAX_IF_COW (1ULL << 1)
+
/*
* By this point grab_mapping_entry() has ensured that we have a locked entry
* of the appropriate size so we don't have to worry about downgrading PMDs to
@@ -714,14 +717,17 @@ static int copy_user_dax(struct block_device *bdev, struct dax_device *dax_dev,
*/
static void *dax_insert_entry(struct xa_state *xas,
struct address_space *mapping, struct vm_fault *vmf,
- void *entry, pfn_t pfn, unsigned long flags, bool dirty)
+ void *entry, pfn_t pfn, unsigned long flags,
+ unsigned int insert_flags)
{
void *new_entry = dax_make_entry(pfn, flags);
+ bool dirty = insert_flags & DAX_IF_DIRTY;
+ bool cow = insert_flags & DAX_IF_COW;
if (dirty)
__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
- if (dax_is_zero_entry(entry) && !(flags & DAX_ZERO_PAGE)) {
+ if (cow || (dax_is_zero_entry(entry) && !(flags & DAX_ZERO_PAGE))) {
unsigned long index = xas->xa_index;
/* we are replacing a zero page with block mapping */
if (dax_is_pmd_entry(entry))
@@ -733,7 +739,7 @@ static void *dax_insert_entry(struct xa_state *xas,
xas_reset(xas);
xas_lock_irq(xas);
- if (dax_is_zero_entry(entry) || dax_is_empty_entry(entry)) {
+ if (cow || dax_is_zero_entry(entry) || dax_is_empty_entry(entry)) {
void *old;
dax_disassociate_entry(entry, mapping, false);
@@ -757,6 +763,9 @@ static void *dax_insert_entry(struct xa_state *xas,
if (dirty)
xas_set_mark(xas, PAGECACHE_TAG_DIRTY);
+ if (cow)
+ xas_set_mark(xas, PAGECACHE_TAG_TOWRITE);
+
xas_unlock_irq(xas);
return entry;
}
@@ -1044,7 +1053,7 @@ static vm_fault_t dax_load_hole(struct xa_state *xas,
vm_fault_t ret;
*entry = dax_insert_entry(xas, mapping, vmf, *entry, pfn,
- DAX_ZERO_PAGE, false);
+ DAX_ZERO_PAGE, 0);
ret = vmf_insert_mixed(vmf->vma, vaddr, pfn);
trace_dax_load_hole(inode, vmf, ret);
@@ -1313,6 +1322,7 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
void *entry;
pfn_t pfn;
void *kaddr;
+ unsigned long insert_flags = 0;
trace_dax_pte_fault(inode, vmf, ret);
/*
@@ -1405,8 +1415,10 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
if (error < 0)
goto error_finish_iomap;
- entry = dax_insert_entry(&xas, mapping, vmf, entry, pfn,
- 0, write && !sync);
+ if (write && !sync)
+ insert_flags |= DAX_IF_DIRTY;
+ entry = dax_insert_entry(&xas, mapping, vmf, entry, pfn, 0,
+ insert_flags);
if (srcmap.type != IOMAP_HOLE) {
error = dax_copy_edges(pos, PAGE_SIZE, &srcmap, kaddr,
@@ -1438,8 +1450,10 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
goto finish_iomap;
case IOMAP_UNWRITTEN:
- if (srcmap.type != IOMAP_HOLE)
+ if (srcmap.type != IOMAP_HOLE) {
+ insert_flags |= DAX_IF_COW;
goto cow;
+ }
/*FALLTHRU*/
case IOMAP_HOLE:
if (!write) {
@@ -1497,7 +1511,7 @@ static vm_fault_t dax_pmd_load_hole(struct xa_state *xas, struct vm_fault *vmf,
pfn = page_to_pfn_t(zero_page);
*entry = dax_insert_entry(xas, mapping, vmf, *entry, pfn,
- DAX_PMD | DAX_ZERO_PAGE, false);
+ DAX_PMD | DAX_ZERO_PAGE, 0);
if (arch_needs_pgtable_deposit()) {
pgtable = pte_alloc_one(vma->vm_mm);
@@ -1549,6 +1563,7 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
int error;
pfn_t pfn;
void *kaddr;
+ unsigned long insert_flags = 0;
/*
* Check whether offset isn't beyond end of file now. Caller is
@@ -1636,8 +1651,11 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
if (error < 0)
goto finish_iomap;
+ if (write && !sync)
+ insert_flags |= DAX_IF_DIRTY;
+
entry = dax_insert_entry(&xas, mapping, vmf, entry, pfn,
- DAX_PMD, write && !sync);
+ DAX_PMD, insert_flags);
if (srcmap.type != IOMAP_HOLE) {
error = dax_copy_edges(pos, PMD_SIZE, &srcmap, kaddr,
@@ -1664,8 +1682,10 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
result = vmf_insert_pfn_pmd(vmf, pfn, write);
break;
case IOMAP_UNWRITTEN:
- if (srcmap.type != IOMAP_HOLE)
+ if (srcmap.type != IOMAP_HOLE) {
+ insert_flags |= DAX_IF_COW;
goto cow;
+ }
/*FALLTHRU*/
case IOMAP_HOLE:
if (WARN_ON_ONCE(write))
--
2.23.0
In fsdax mode, WRITE and ZERO on a shared extent need COW mechanism
performed. After COW, new extents needs to be remapped to the file.
Signed-off-by: Shiyang Ruan <[email protected]>
---
fs/xfs/xfs_bmap_util.c | 6 +++++-
fs/xfs/xfs_file.c | 10 +++++++---
fs/xfs/xfs_iomap.c | 3 ++-
fs/xfs/xfs_iops.c | 11 ++++++++---
fs/xfs/xfs_reflink.c | 2 ++
5 files changed, 24 insertions(+), 8 deletions(-)
diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
index 99bf372ed551..1b7d0665d889 100644
--- a/fs/xfs/xfs_bmap_util.c
+++ b/fs/xfs/xfs_bmap_util.c
@@ -1114,10 +1114,14 @@ xfs_free_file_space(
if (offset + len > XFS_ISIZE(ip))
len = XFS_ISIZE(ip) - offset;
error = iomap_zero_range(VFS_I(ip), offset, len, NULL,
- &xfs_buffered_write_iomap_ops);
+ IS_DAX(VFS_I(ip)) ?
+ &xfs_direct_write_iomap_ops : &xfs_buffered_write_iomap_ops);
if (error)
return error;
+ if (xfs_is_reflink_inode(ip))
+ xfs_reflink_end_cow(ip, offset, len);
+
/*
* If we zeroed right up to EOF and EOF straddles a page boundary we
* must make sure that the post-EOF area is also zeroed because the
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 24659667d5cb..48071f16a436 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -594,9 +594,13 @@ xfs_file_dax_write(
trace_xfs_file_dax_write(ip, count, pos);
ret = dax_iomap_rw(iocb, from, &xfs_direct_write_iomap_ops);
- if (ret > 0 && iocb->ki_pos > i_size_read(inode)) {
- i_size_write(inode, iocb->ki_pos);
- error = xfs_setfilesize(ip, pos, ret);
+ if (ret > 0) {
+ if (iocb->ki_pos > i_size_read(inode)) {
+ i_size_write(inode, iocb->ki_pos);
+ error = xfs_setfilesize(ip, pos, ret);
+ }
+ if (xfs_is_cow_inode(ip))
+ xfs_reflink_end_cow(ip, pos, ret);
}
out:
xfs_iunlock(ip, iolock);
diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index e8fb500e1880..db8ee371252f 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -772,13 +772,14 @@ xfs_direct_write_iomap_begin(
goto out_unlock;
if (imap_needs_cow(ip, flags, &imap, nimaps)) {
+ bool need_convert = flags & IOMAP_DIRECT || IS_DAX(inode);
error = -EAGAIN;
if (flags & IOMAP_NOWAIT)
goto out_unlock;
/* may drop and re-acquire the ilock */
error = xfs_reflink_allocate_cow(ip, &imap, &cmap, &shared,
- &lockmode, flags & IOMAP_DIRECT);
+ &lockmode, need_convert);
if (error)
goto out_unlock;
if (shared)
diff --git a/fs/xfs/xfs_iops.c b/fs/xfs/xfs_iops.c
index 329a34af8e79..0052a97ccebf 100644
--- a/fs/xfs/xfs_iops.c
+++ b/fs/xfs/xfs_iops.c
@@ -834,6 +834,7 @@ xfs_setattr_size(
int error;
uint lock_flags = 0;
bool did_zeroing = false;
+ const struct iomap_ops *ops;
ASSERT(xfs_isilocked(ip, XFS_IOLOCK_EXCL));
ASSERT(xfs_isilocked(ip, XFS_MMAPLOCK_EXCL));
@@ -880,13 +881,17 @@ xfs_setattr_size(
* extension, or zeroing out the rest of the block on a downward
* truncate.
*/
+ if (IS_DAX(inode))
+ ops = &xfs_direct_write_iomap_ops;
+ else
+ ops = &xfs_buffered_write_iomap_ops;
+
if (newsize > oldsize) {
trace_xfs_zero_eof(ip, oldsize, newsize - oldsize);
error = iomap_zero_range(inode, oldsize, newsize - oldsize,
- &did_zeroing, &xfs_buffered_write_iomap_ops);
+ &did_zeroing, ops);
} else {
- error = iomap_truncate_page(inode, newsize, &did_zeroing,
- &xfs_buffered_write_iomap_ops);
+ error = iomap_truncate_page(inode, newsize, &did_zeroing, ops);
}
if (error)
diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index 2c8ad581d4db..e3620bc794a2 100644
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -1270,6 +1270,8 @@ xfs_reflink_zero_posteof(
trace_xfs_zero_eof(ip, isize, pos - isize);
return iomap_zero_range(VFS_I(ip), isize, pos - isize, NULL,
+ IS_DAX(VFS_I(ip)) ?
+ &xfs_direct_write_iomap_ops :
&xfs_buffered_write_iomap_ops);
}
--
2.23.0
From: Goldwyn Rodrigues <[email protected]>
However, this needed more iomap fields, so it was easier
to pass iomap and compute inside the function rather
than passing a log of arguments.
Note, there is subtle difference between iomap_sector and
dax_iomap_sector(). Can we replace dax_iomap_sector with
iomap_sector()? It would need pos & PAGE_MASK though or else
bdev_dax_pgoff() return -EINVAL.
Signed-off-by: Goldwyn Rodrigues <[email protected]>
---
fs/dax.c | 21 ++++++++++++++++-----
fs/iomap/buffered-io.c | 8 ++++----
include/linux/dax.h | 12 ++++++------
3 files changed, 26 insertions(+), 15 deletions(-)
diff --git a/fs/dax.c b/fs/dax.c
index a4f90f3faddb..eab6bb256205 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1117,11 +1117,16 @@ static int dax_copy_edges(loff_t pos, loff_t length, struct iomap *srcmap,
return ret;
}
-int __dax_zero_page_range(struct block_device *bdev,
- struct dax_device *dax_dev, sector_t sector,
- unsigned int offset, unsigned int size)
+int __dax_zero_page_range(struct iomap *iomap, struct iomap *srcmap, loff_t pos,
+ unsigned int offset, unsigned int size)
{
- if (dax_range_is_aligned(bdev, offset, size)) {
+ sector_t sector = dax_iomap_sector(iomap, pos & PAGE_MASK);
+ struct block_device *bdev = iomap->bdev;
+ struct dax_device *dax_dev = iomap->dax_dev;
+ int ret = 0;
+
+ if (iomap == srcmap &&
+ dax_range_is_aligned(bdev, offset, size)) {
sector_t start_sector = sector + (offset >> 9);
return blkdev_issue_zeroout(bdev, start_sector,
@@ -1141,11 +1146,17 @@ int __dax_zero_page_range(struct block_device *bdev,
dax_read_unlock(id);
return rc;
}
+ if (iomap != srcmap) {
+ ret = dax_copy_edges(pos, size, srcmap, kaddr, false);
+ if (ret)
+ goto out_unlock;
+ }
memset(kaddr + offset, 0, size);
dax_flush(dax_dev, kaddr + offset, size);
+out_unlock:
dax_read_unlock(id);
}
- return 0;
+ return ret;
}
EXPORT_SYMBOL_GPL(__dax_zero_page_range);
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index c62e807956b6..3fa79389e4d0 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -960,10 +960,9 @@ static int iomap_zero(struct inode *inode, loff_t pos, unsigned offset,
}
static int iomap_dax_zero(loff_t pos, unsigned offset, unsigned bytes,
- struct iomap *iomap)
+ struct iomap *iomap, struct iomap *srcmap)
{
- return __dax_zero_page_range(iomap->bdev, iomap->dax_dev,
- iomap_sector(iomap, pos & PAGE_MASK), offset, bytes);
+ return __dax_zero_page_range(iomap, srcmap, pos, offset, bytes);
}
static loff_t
@@ -985,7 +984,8 @@ iomap_zero_range_actor(struct inode *inode, loff_t pos, loff_t count,
bytes = min_t(loff_t, PAGE_SIZE - offset, count);
if (IS_DAX(inode))
- status = iomap_dax_zero(pos, offset, bytes, iomap);
+ status = iomap_dax_zero(pos, offset, bytes, iomap,
+ srcmap);
else
status = iomap_zero(inode, pos, offset, bytes, iomap,
srcmap);
diff --git a/include/linux/dax.h b/include/linux/dax.h
index 4533bfb99683..7adf3b9e1061 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -12,6 +12,7 @@
typedef unsigned long dax_entry_t;
+struct iomap;
struct iomap_ops;
struct dax_device;
struct dax_operations {
@@ -226,13 +227,12 @@ int dax_file_range_compare(struct inode *src, loff_t srcoff,
const struct iomap_ops *ops);
#ifdef CONFIG_FS_DAX
-int __dax_zero_page_range(struct block_device *bdev,
- struct dax_device *dax_dev, sector_t sector,
- unsigned int offset, unsigned int length);
+int __dax_zero_page_range(struct iomap *iomap, struct iomap *srcmap, loff_t pos,
+ unsigned int offset, unsigned int size);
#else
-static inline int __dax_zero_page_range(struct block_device *bdev,
- struct dax_device *dax_dev, sector_t sector,
- unsigned int offset, unsigned int length)
+static inline int __dax_zero_page_range(struct iomap *iomap,
+ struct iomap *srcmap, loff_t pos,
+ unsigned int offset, unsigned int size)
{
return -ENXIO;
}
--
2.23.0
Use xfs_break_layouts() to break files' layouts when locking them. And
call dax_file_range_compare() function to compare range for DAX files.
Signed-off-by: Shiyang Ruan <[email protected]>
---
fs/xfs/xfs_reflink.c | 77 ++++++++++++++++++++++++++------------------
1 file changed, 45 insertions(+), 32 deletions(-)
diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index e3620bc794a2..3d8d1d2f0ac0 100644
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -1186,47 +1186,41 @@ xfs_reflink_remap_blocks(
* back out both locks.
*/
static int
-xfs_iolock_two_inodes_and_break_layout(
- struct inode *src,
- struct inode *dest)
+xfs_reflink_remap_lock_and_break_layouts(
+ struct file *file_in,
+ struct file *file_out)
{
int error;
+ struct inode *inode_in = file_inode(file_in);
+ struct xfs_inode *src = XFS_I(inode_in);
+ struct inode *inode_out = file_inode(file_out);
+ struct xfs_inode *dest = XFS_I(inode_out);
+ uint iolock = XFS_IOLOCK_EXCL | XFS_MMAPLOCK_EXCL;
- if (src > dest)
+ if (inode_in > inode_out) {
+ swap(inode_in, inode_out);
swap(src, dest);
-
-retry:
- /* Wait to break both inodes' layouts before we start locking. */
- error = break_layout(src, true);
- if (error)
- return error;
- if (src != dest) {
- error = break_layout(dest, true);
- if (error)
- return error;
}
- /* Lock one inode and make sure nobody got in and leased it. */
- inode_lock(src);
- error = break_layout(src, false);
+ inode_lock(inode_in);
+ xfs_ilock(src, XFS_MMAPLOCK_EXCL);
+ error = xfs_break_layouts(inode_in, &iolock, BREAK_UNMAP);
+ xfs_iunlock(src, XFS_MMAPLOCK_EXCL);
if (error) {
- inode_unlock(src);
- if (error == -EWOULDBLOCK)
- goto retry;
+ inode_unlock(inode_in);
return error;
}
- if (src == dest)
+ if (inode_in == inode_out)
return 0;
- /* Lock the other inode and make sure nobody got in and leased it. */
- inode_lock_nested(dest, I_MUTEX_NONDIR2);
- error = break_layout(dest, false);
+ inode_lock_nested(inode_out, I_MUTEX_NONDIR2);
+ xfs_ilock(dest, XFS_MMAPLOCK_EXCL);
+ error = xfs_break_layouts(inode_out, &iolock, BREAK_UNMAP);
+ xfs_iunlock(dest, XFS_MMAPLOCK_EXCL);
if (error) {
- inode_unlock(src);
- inode_unlock(dest);
- if (error == -EWOULDBLOCK)
- goto retry;
+ inode_unlock(inode_in);
+ inode_unlock(inode_out);
return error;
}
@@ -1245,6 +1239,11 @@ xfs_reflink_remap_unlock(
struct xfs_inode *dest = XFS_I(inode_out);
bool same_inode = (inode_in == inode_out);
+ if (inode_in > inode_out) {
+ swap(inode_in, inode_out);
+ swap(src, dest);
+ }
+
xfs_iunlock(dest, XFS_MMAPLOCK_EXCL);
if (!same_inode)
xfs_iunlock(src, XFS_MMAPLOCK_EXCL);
@@ -1275,6 +1274,14 @@ xfs_reflink_zero_posteof(
&xfs_buffered_write_iomap_ops);
}
+int xfs_reflink_dedupe_file_range_compare(struct inode *src, loff_t srcoff,
+ struct inode *dest, loff_t destoff,
+ loff_t len, bool *is_same)
+{
+ return dax_file_range_compare(src, srcoff, dest, destoff, len, is_same,
+ &xfs_read_iomap_ops);
+}
+
/*
* Prepare two files for range cloning. Upon a successful return both inodes
* will have the iolock and mmaplock held, the page cache of the out file will
@@ -1319,9 +1326,10 @@ xfs_reflink_remap_prep(
struct xfs_inode *dest = XFS_I(inode_out);
bool same_inode = (inode_in == inode_out);
ssize_t ret;
+ compare_range_t cmp;
/* Lock both files against IO */
- ret = xfs_iolock_two_inodes_and_break_layout(inode_in, inode_out);
+ ret = xfs_reflink_remap_lock_and_break_layouts(file_in, file_out);
if (ret)
return ret;
if (same_inode)
@@ -1336,12 +1344,17 @@ xfs_reflink_remap_prep(
if (XFS_IS_REALTIME_INODE(src) || XFS_IS_REALTIME_INODE(dest))
goto out_unlock;
- /* Don't share DAX file data for now. */
- if (IS_DAX(inode_in) || IS_DAX(inode_out))
+ /* Don't share DAX file data with non-DAX file. */
+ if (IS_DAX(inode_in) != IS_DAX(inode_out))
goto out_unlock;
+ if (IS_DAX(inode_in))
+ cmp = xfs_reflink_dedupe_file_range_compare;
+ else
+ cmp = vfs_dedupe_file_range_compare;
+
ret = generic_remap_file_range_prep(file_in, pos_in, file_out, pos_out,
- len, remap_flags, vfs_dedupe_file_range_compare);
+ len, remap_flags, cmp);
if (ret < 0 || *len == 0)
goto out_unlock;
--
2.23.0
From: Goldwyn Rodrigues <[email protected]>
With dax we cannot deal with readpage() etc. So, we create a
funciton callback to perform the file data comparison and pass
it to generic_remap_file_range_prep() so it can use iomap-based
functions.
This may not be the best way to solve this. Suggestions welcome.
Signed-off-by: Goldwyn Rodrigues <[email protected]>
Signed-off-by: Shiyang Ruan <[email protected]>
---
fs/btrfs/ioctl.c | 3 ++-
fs/dax.c | 58 ++++++++++++++++++++++++++++++++++++++++++++
fs/ocfs2/file.c | 2 +-
fs/read_write.c | 11 +++++----
fs/xfs/xfs_reflink.c | 2 +-
include/linux/dax.h | 4 +++
include/linux/fs.h | 9 ++++++-
7 files changed, 80 insertions(+), 9 deletions(-)
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index de730e56d3f5..ee16e275c44a 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -3910,7 +3910,8 @@ static int btrfs_remap_file_range_prep(struct file *file_in, loff_t pos_in,
return ret;
return generic_remap_file_range_prep(file_in, pos_in, file_out, pos_out,
- len, remap_flags);
+ len, remap_flags,
+ vfs_dedupe_file_range_compare);
}
loff_t btrfs_remap_file_range(struct file *src_file, loff_t off,
diff --git a/fs/dax.c b/fs/dax.c
index e6174c0c669a..a4f90f3faddb 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -30,6 +30,8 @@
#define CREATE_TRACE_POINTS
#include <trace/events/fs_dax.h>
+#define MIN(a, b) (((a) < (b)) ? (a) : (b))
+
static inline unsigned int pe_order(enum page_entry_size pe_size)
{
if (pe_size == PE_SIZE_PTE)
@@ -1826,3 +1828,59 @@ vm_fault_t dax_finish_sync_fault(struct vm_fault *vmf,
return dax_insert_pfn_mkwrite(vmf, pfn, order);
}
EXPORT_SYMBOL_GPL(dax_finish_sync_fault);
+
+int dax_file_range_compare(struct inode *src, loff_t srcoff, struct inode *dest,
+ loff_t destoff, loff_t len, bool *is_same, const struct iomap_ops *ops)
+{
+ void *saddr, *daddr;
+ struct iomap s_iomap = {0};
+ struct iomap d_iomap = {0};
+ bool same = true;
+ loff_t cmp_len;
+ int id, ret = 0;
+
+ id = dax_read_lock();
+ while (len) {
+ ret = ops->iomap_begin(src, srcoff, len, 0, &s_iomap, NULL);
+ if (ret < 0) {
+ if (ops->iomap_end)
+ ops->iomap_end(src, srcoff, len, ret, 0, &s_iomap);
+ return ret;
+ }
+ cmp_len = len;
+ cmp_len = MIN(len, s_iomap.offset + s_iomap.length - srcoff);
+
+ ret = ops->iomap_begin(dest, destoff, cmp_len, 0, &d_iomap, NULL);
+ if (ret < 0) {
+ if (ops->iomap_end) {
+ ops->iomap_end(src, srcoff, len, ret, 0, &s_iomap);
+ ops->iomap_end(dest, destoff, len, ret, 0, &d_iomap);
+ }
+ return ret;
+ }
+ cmp_len = MIN(cmp_len, d_iomap.offset + d_iomap.length - destoff);
+
+ dax_iomap_direct_access(&s_iomap, srcoff,
+ ALIGN(srcoff + cmp_len, PAGE_SIZE),
+ NULL, &saddr);
+ dax_iomap_direct_access(&d_iomap, destoff,
+ ALIGN(destoff + cmp_len, PAGE_SIZE),
+ NULL, &daddr);
+
+ same = !memcmp(saddr, daddr, cmp_len);
+ if (!same)
+ break;
+ len -= cmp_len;
+ srcoff += cmp_len;
+ destoff += cmp_len;
+
+ if (ops->iomap_end) {
+ ret = ops->iomap_end(src, srcoff, len, 0, 0, &s_iomap);
+ ret = ops->iomap_end(dest, destoff, len, 0, 0, &d_iomap);
+ }
+ }
+ dax_read_unlock(id);
+ *is_same = same;
+ return ret;
+}
+EXPORT_SYMBOL_GPL(dax_file_range_compare);
diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
index 2e982db3e1ae..f29315d2e26b 100644
--- a/fs/ocfs2/file.c
+++ b/fs/ocfs2/file.c
@@ -2545,7 +2545,7 @@ static loff_t ocfs2_remap_file_range(struct file *file_in, loff_t pos_in,
goto out_unlock;
ret = generic_remap_file_range_prep(file_in, pos_in, file_out, pos_out,
- &len, remap_flags);
+ &len, remap_flags, vfs_dedupe_file_range_compare);
if (ret < 0 || len == 0)
goto out_unlock;
diff --git a/fs/read_write.c b/fs/read_write.c
index 5bbf587f5bc1..9c7a8320a260 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1853,7 +1853,7 @@ static void vfs_unlock_two_pages(struct page *page1, struct page *page2)
* Compare extents of two files to see if they are the same.
* Caller must have locked both inodes to prevent write races.
*/
-static int vfs_dedupe_file_range_compare(struct inode *src, loff_t srcoff,
+int vfs_dedupe_file_range_compare(struct inode *src, loff_t srcoff,
struct inode *dest, loff_t destoff,
loff_t len, bool *is_same)
{
@@ -1934,6 +1934,7 @@ static int vfs_dedupe_file_range_compare(struct inode *src, loff_t srcoff,
out_error:
return error;
}
+EXPORT_SYMBOL_GPL(vfs_dedupe_file_range_compare);
/*
* Check that the two inodes are eligible for cloning, the ranges make
@@ -1945,7 +1946,8 @@ static int vfs_dedupe_file_range_compare(struct inode *src, loff_t srcoff,
*/
int generic_remap_file_range_prep(struct file *file_in, loff_t pos_in,
struct file *file_out, loff_t pos_out,
- loff_t *len, unsigned int remap_flags)
+ loff_t *len, unsigned int remap_flags,
+ compare_range_t compare)
{
struct inode *inode_in = file_inode(file_in);
struct inode *inode_out = file_inode(file_out);
@@ -2004,9 +2006,8 @@ int generic_remap_file_range_prep(struct file *file_in, loff_t pos_in,
*/
if (remap_flags & REMAP_FILE_DEDUP) {
bool is_same = false;
-
- ret = vfs_dedupe_file_range_compare(inode_in, pos_in,
- inode_out, pos_out, *len, &is_same);
+ ret = (*compare)(inode_in, pos_in,
+ inode_out, pos_out, *len, &is_same);
if (ret)
return ret;
if (!is_same)
diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index de451235c4ee..2c8ad581d4db 100644
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -1339,7 +1339,7 @@ xfs_reflink_remap_prep(
goto out_unlock;
ret = generic_remap_file_range_prep(file_in, pos_in, file_out, pos_out,
- len, remap_flags);
+ len, remap_flags, vfs_dedupe_file_range_compare);
if (ret < 0 || *len == 0)
goto out_unlock;
diff --git a/include/linux/dax.h b/include/linux/dax.h
index 9bd8528bd305..4533bfb99683 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -220,6 +220,10 @@ vm_fault_t dax_finish_sync_fault(struct vm_fault *vmf,
int dax_delete_mapping_entry(struct address_space *mapping, pgoff_t index);
int dax_invalidate_mapping_entry_sync(struct address_space *mapping,
pgoff_t index);
+int dax_file_range_compare(struct inode *src, loff_t srcoff,
+ struct inode *dest, loff_t destoff,
+ loff_t len, bool *is_same,
+ const struct iomap_ops *ops);
#ifdef CONFIG_FS_DAX
int __dax_zero_page_range(struct block_device *bdev,
diff --git a/include/linux/fs.h b/include/linux/fs.h
index e0d909d35763..ac5755f70995 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1912,13 +1912,20 @@ extern ssize_t vfs_readv(struct file *, const struct iovec __user *,
unsigned long, loff_t *, rwf_t);
extern ssize_t vfs_copy_file_range(struct file *, loff_t , struct file *,
loff_t, size_t, unsigned int);
+extern int vfs_dedupe_file_range_compare(struct inode *src, loff_t srcoff,
+ struct inode *dest, loff_t destoff,
+ loff_t len, bool *is_same);
+typedef int (*compare_range_t)(struct inode *src, loff_t srcpos,
+ struct inode *dest, loff_t destpos,
+ loff_t len, bool *is_same);
extern ssize_t generic_copy_file_range(struct file *file_in, loff_t pos_in,
struct file *file_out, loff_t pos_out,
size_t len, unsigned int flags);
extern int generic_remap_file_range_prep(struct file *file_in, loff_t pos_in,
struct file *file_out, loff_t pos_out,
loff_t *count,
- unsigned int remap_flags);
+ unsigned int remap_flags,
+ compare_range_t cmp);
extern loff_t do_clone_file_range(struct file *file_in, loff_t pos_in,
struct file *file_out, loff_t pos_out,
loff_t len, unsigned int remap_flags);
--
2.23.0
Add dax_copy_edges() into each dax actor functions to perform
copy on write.
Signed-off-by: Shiyang Ruan <[email protected]>
---
fs/dax.c | 36 +++++++++++++++++++++++++++++++++---
1 file changed, 33 insertions(+), 3 deletions(-)
diff --git a/fs/dax.c b/fs/dax.c
index e1f4493ce56a..949a40cf1fe7 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1159,7 +1159,7 @@ dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
return iov_iter_zero(min(length, end - pos), iter);
}
- if (WARN_ON_ONCE(iomap->type != IOMAP_MAPPED))
+ if (WARN_ON_ONCE(iomap->type != IOMAP_MAPPED && iomap == srcmap))
return -EIO;
/*
@@ -1198,6 +1198,12 @@ dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
break;
}
+ if (iomap != srcmap) {
+ ret = dax_copy_edges(pos, length, srcmap, kaddr, false);
+ if (ret)
+ break;
+ }
+
map_len = PFN_PHYS(map_len);
kaddr += offset;
map_len -= offset;
@@ -1306,6 +1312,7 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
vm_fault_t ret = 0;
void *entry;
pfn_t pfn;
+ void *kaddr;
trace_dax_pte_fault(inode, vmf, ret);
/*
@@ -1387,19 +1394,27 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
switch (iomap.type) {
case IOMAP_MAPPED:
+cow:
if (iomap.flags & IOMAP_F_NEW) {
count_vm_event(PGMAJFAULT);
count_memcg_event_mm(vma->vm_mm, PGMAJFAULT);
major = VM_FAULT_MAJOR;
}
error = dax_iomap_direct_access(&iomap, pos, PAGE_SIZE, &pfn,
- NULL);
+ &kaddr);
if (error < 0)
goto error_finish_iomap;
entry = dax_insert_entry(&xas, mapping, vmf, entry, pfn,
0, write && !sync);
+ if (srcmap.type != IOMAP_HOLE) {
+ error = dax_copy_edges(pos, PAGE_SIZE, &srcmap, kaddr,
+ false);
+ if (error)
+ goto error_finish_iomap;
+ }
+
/*
* If we are doing synchronous page fault and inode needs fsync,
* we can insert PTE into page tables only after that happens.
@@ -1423,6 +1438,9 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
goto finish_iomap;
case IOMAP_UNWRITTEN:
+ if (srcmap.type != IOMAP_HOLE)
+ goto cow;
+ /*FALLTHRU*/
case IOMAP_HOLE:
if (!write) {
ret = dax_load_hole(&xas, mapping, &entry, vmf);
@@ -1530,6 +1548,7 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
loff_t pos;
int error;
pfn_t pfn;
+ void *kaddr;
/*
* Check whether offset isn't beyond end of file now. Caller is
@@ -1610,15 +1629,23 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
sync = dax_fault_is_synchronous(iomap_flags, vma, &iomap);
switch (iomap.type) {
+cow:
case IOMAP_MAPPED:
error = dax_iomap_direct_access(&iomap, pos, PMD_SIZE, &pfn,
- NULL);
+ &kaddr);
if (error < 0)
goto finish_iomap;
entry = dax_insert_entry(&xas, mapping, vmf, entry, pfn,
DAX_PMD, write && !sync);
+ if (srcmap.type != IOMAP_HOLE) {
+ error = dax_copy_edges(pos, PMD_SIZE, &srcmap, kaddr,
+ true);
+ if (error)
+ goto unlock_entry;
+ }
+
/*
* If we are doing synchronous page fault and inode needs fsync,
* we can insert PMD into page tables only after that happens.
@@ -1637,6 +1664,9 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
result = vmf_insert_pfn_pmd(vmf, pfn, write);
break;
case IOMAP_UNWRITTEN:
+ if (srcmap.type != IOMAP_HOLE)
+ goto cow;
+ /*FALLTHRU*/
case IOMAP_HOLE:
if (WARN_ON_ONCE(write))
break;
--
2.23.0
To copy source data to destance address before write. Change
dax_iomap_pfn() to return the address as well in order to use it for
performing a memcpy in case the type is IOMAP_COW.
dax_copy_edges() is a helper functions performs a copy from one part of
the device to another for data not page aligned.
Signed-off-by: Goldwyn Rodrigues <[email protected]>
Signed-off-by: Shiyang Ruan <[email protected]>
---
fs/dax.c | 64 ++++++++++++++++++++++++++++++++++++++++++++++++++------
1 file changed, 58 insertions(+), 6 deletions(-)
diff --git a/fs/dax.c b/fs/dax.c
index 68eef98cd9c4..e1f4493ce56a 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -987,8 +987,8 @@ static sector_t dax_iomap_sector(struct iomap *iomap, loff_t pos)
return (iomap->addr + (pos & PAGE_MASK) - iomap->offset) >> 9;
}
-static int dax_iomap_pfn(struct iomap *iomap, loff_t pos, size_t size,
- pfn_t *pfnp)
+static int dax_iomap_direct_access(struct iomap *iomap, loff_t pos, size_t size,
+ pfn_t *pfnp, void **addr)
{
const sector_t sector = dax_iomap_sector(iomap, pos);
pgoff_t pgoff;
@@ -999,12 +999,14 @@ static int dax_iomap_pfn(struct iomap *iomap, loff_t pos, size_t size,
if (rc)
return rc;
id = dax_read_lock();
- length = dax_direct_access(iomap->dax_dev, pgoff, PHYS_PFN(size),
- NULL, pfnp);
+ length = dax_direct_access(iomap->dax_dev, pgoff, PHYS_PFN(size), addr,
+ pfnp);
if (length < 0) {
rc = length;
goto out;
}
+ if (!pfnp)
+ goto out_check_addr;
rc = -EINVAL;
if (PFN_PHYS(length) < size)
goto out;
@@ -1014,6 +1016,12 @@ static int dax_iomap_pfn(struct iomap *iomap, loff_t pos, size_t size,
if (length > 1 && !pfn_t_devmap(*pfnp))
goto out;
rc = 0;
+
+out_check_addr:
+ if (!addr)
+ goto out;
+ if (!*addr)
+ rc = -EFAULT;
out:
dax_read_unlock(id);
return rc;
@@ -1056,6 +1064,48 @@ static bool dax_range_is_aligned(struct block_device *bdev,
return true;
}
+/*
+ * dax_copy_edges - Copies the part of the pages not included in
+ * the write, but required for CoW because
+ * offset/offset+length are not page aligned.
+ */
+static int dax_copy_edges(loff_t pos, loff_t length, struct iomap *srcmap,
+ void *daddr, bool pmd)
+{
+ size_t page_size = pmd ? PMD_SIZE : PAGE_SIZE;
+ loff_t offset = pos & (page_size - 1);
+ size_t size = ALIGN(offset + length, page_size);
+ loff_t end = pos + length;
+ loff_t pg_end = round_up(end, page_size);
+ void *saddr = 0;
+ int ret = 0;
+
+ ret = dax_iomap_direct_access(srcmap, pos, size, NULL, &saddr);
+ if (ret)
+ return ret;
+ /*
+ * Copy the first part of the page
+ * Note: we pass offset as length
+ */
+ if (offset) {
+ if (saddr)
+ ret = memcpy_mcsafe(daddr, saddr, offset);
+ else
+ memset(daddr, 0, offset);
+ }
+
+ /* Copy the last part of the range */
+ if (end < pg_end) {
+ if (saddr)
+ ret = memcpy_mcsafe(daddr + offset + length,
+ saddr + offset + length, pg_end - end);
+ else
+ memset(daddr + offset + length, 0,
+ pg_end - end);
+ }
+ return ret;
+}
+
int __dax_zero_page_range(struct block_device *bdev,
struct dax_device *dax_dev, sector_t sector,
unsigned int offset, unsigned int size)
@@ -1342,7 +1392,8 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
count_memcg_event_mm(vma->vm_mm, PGMAJFAULT);
major = VM_FAULT_MAJOR;
}
- error = dax_iomap_pfn(&iomap, pos, PAGE_SIZE, &pfn);
+ error = dax_iomap_direct_access(&iomap, pos, PAGE_SIZE, &pfn,
+ NULL);
if (error < 0)
goto error_finish_iomap;
@@ -1560,7 +1611,8 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
switch (iomap.type) {
case IOMAP_MAPPED:
- error = dax_iomap_pfn(&iomap, pos, PMD_SIZE, &pfn);
+ error = dax_iomap_direct_access(&iomap, pos, PMD_SIZE, &pfn,
+ NULL);
if (error < 0)
goto finish_iomap;
--
2.23.0
On 12:13 30/10, Shiyang Ruan wrote:
> This patchset aims to take care of this issue to make reflink and dedupe
> work correctly (actually in read/write path, there still has some problems,
> such as the page->mapping and page->index issue, in mmap path) in XFS under
> fsdax mode.
Have you managed to solve the problem of multi-mapped pages? I don't
think we can include this until we solve that problem. This is the
problem I faced when I was doing the btrfs dax support.
Suppose there is an extent shared with multiple files. You map data for
both files. Which inode should page->mapping->host (precisely
page->mapping) point to? As Dave pointed out, this needs to be fixed at
the mm level, and will not only benefit dax with CoW but other
areas such as overlayfs and possibly containers.
--
Goldwyn
>
> It is based on Goldwyn's patchsets: "v4 Btrfs dax support" and the latest
> iomap. I borrowed some patches related and made a few fix to make it
> basically works fine.
>
> For dax framework:
> 1. adapt to the latest change in iomap (two iomaps).
>
> For XFS:
> 1. distinguish dax write/zero from normal write/zero.
> 2. remap extents after COW.
> 3. add file contents comparison function based on dax framework.
> 4. use xfs_break_layouts() instead of break_layout to support dax.
>
>
> Goldwyn Rodrigues (3):
> dax: replace mmap entry in case of CoW
> fs: dedup file range to use a compare function
> dax: memcpy before zeroing range
>
> Shiyang Ruan (4):
> dax: Introduce dax_copy_edges() for COW.
> dax: copy data before write.
> xfs: handle copy-on-write in fsdax write() path.
> xfs: support dedupe for fsdax.
>
> fs/btrfs/ioctl.c | 3 +-
> fs/dax.c | 211 +++++++++++++++++++++++++++++++++++++----
> fs/iomap/buffered-io.c | 8 +-
> fs/ocfs2/file.c | 2 +-
> fs/read_write.c | 11 ++-
> fs/xfs/xfs_bmap_util.c | 6 +-
> fs/xfs/xfs_file.c | 10 +-
> fs/xfs/xfs_iomap.c | 3 +-
> fs/xfs/xfs_iops.c | 11 ++-
> fs/xfs/xfs_reflink.c | 79 ++++++++-------
> include/linux/dax.h | 16 ++--
> include/linux/fs.h | 9 +-
> 12 files changed, 291 insertions(+), 78 deletions(-)
>
> --
> 2.23.0
>
>
>
--
Goldwyn
On 10/30/19 7:48 PM, Goldwyn Rodrigues wrote:
> On 12:13 30/10, Shiyang Ruan wrote:
>> This patchset aims to take care of this issue to make reflink and dedupe
>> work correctly (actually in read/write path, there still has some problems,
>> such as the page->mapping and page->index issue, in mmap path) in XFS under
>> fsdax mode.
>
> Have you managed to solve the problem of multi-mapped pages? I don't
> think we can include this until we solve that problem. This is the
> problem I faced when I was doing the btrfs dax support.
That problem still exists, didn't be solved in this patchset. But I am
also looking into it. As you know, it's a bit difficult.
Since the iomap for cow is merged in for-next tree, I think it's time to
update this in order to get some comments.
>
> Suppose there is an extent shared with multiple files. You map data for
> both files. Which inode should page->mapping->host (precisely
> page->mapping) point to? As Dave pointed out, this needs to be fixed at
> the mm level, and will not only benefit dax with CoW but other
> areas such as overlayfs and possibly containers.
Yes, I will try to figure out a solution.
>
--
Thanks,
Shiyang Ruan.
Hi Darrick, Dave,
Do you have any comment on this?
On 10/30/19 12:13 PM, Shiyang Ruan wrote:
> This patchset aims to take care of this issue to make reflink and dedupe
> work correctly (actually in read/write path, there still has some problems,
> such as the page->mapping and page->index issue, in mmap path) in XFS under
> fsdax mode.
>
> It is based on Goldwyn's patchsets: "v4 Btrfs dax support" and the latest
> iomap. I borrowed some patches related and made a few fix to make it
> basically works fine.
>
> For dax framework:
> 1. adapt to the latest change in iomap (two iomaps).
>
> For XFS:
> 1. distinguish dax write/zero from normal write/zero.
> 2. remap extents after COW.
> 3. add file contents comparison function based on dax framework.
> 4. use xfs_break_layouts() instead of break_layout to support dax.
>
>
> Goldwyn Rodrigues (3):
> dax: replace mmap entry in case of CoW
> fs: dedup file range to use a compare function
> dax: memcpy before zeroing range
>
> Shiyang Ruan (4):
> dax: Introduce dax_copy_edges() for COW.
> dax: copy data before write.
> xfs: handle copy-on-write in fsdax write() path.
> xfs: support dedupe for fsdax.
>
> fs/btrfs/ioctl.c | 3 +-
> fs/dax.c | 211 +++++++++++++++++++++++++++++++++++++----
> fs/iomap/buffered-io.c | 8 +-
> fs/ocfs2/file.c | 2 +-
> fs/read_write.c | 11 ++-
> fs/xfs/xfs_bmap_util.c | 6 +-
> fs/xfs/xfs_file.c | 10 +-
> fs/xfs/xfs_iomap.c | 3 +-
> fs/xfs/xfs_iops.c | 11 ++-
> fs/xfs/xfs_reflink.c | 79 ++++++++-------
> include/linux/dax.h | 16 ++--
> include/linux/fs.h | 9 +-
> 12 files changed, 291 insertions(+), 78 deletions(-)
>
--
Thanks,
Shiyang Ruan.
On Thu, Nov 7, 2019 at 7:11 PM Shiyang Ruan <[email protected]> wrote:
>
> Hi Darrick, Dave,
>
> Do you have any comment on this?
Christoph pointed out at ALPSS that this problem has significant
overlap with the shared page-cache for reflink problem. So I think we
need to solve that first and then circle back to dax reflink support.
I'm starting to take a look at that.
On Thu, Nov 07, 2019 at 07:30:32PM -0800, Dan Williams wrote:
> On Thu, Nov 7, 2019 at 7:11 PM Shiyang Ruan <[email protected]> wrote:
> >
> > Hi Darrick, Dave,
> >
> > Do you have any comment on this?
>
> Christoph pointed out at ALPSS that this problem has significant
> overlap with the shared page-cache for reflink problem. So I think we
> need to solve that first and then circle back to dax reflink support.
> I'm starting to take a look at that.
I think the DAX side is somewhat simpler because it doesn't really
need to involve the page cache and we don't have to worry about
subtly breaking random filesystems. Hence I'd suggest we sort out a
solution for DAX first, then worry about page cache stuff. The
shared page cache for reflink feature is not a show stopper -
multiple references for DAX is a show stopper. Let's deal with the
DAX problem first.
Cheers,
-Dave.
--
Dave Chinner
[email protected]