Re: [PATCH v9 8/8] xfs: Add dax dedupe support

From: Shiyang Ruan
Date: Thu Sep 16 2021 - 00:01:35 EST



On 2021/9/16 8:30, Darrick J. Wong wrote:
On Wed, Sep 15, 2021 at 06:45:01PM +0800, Shiyang Ruan wrote:
Introduce xfs_mmaplock_two_inodes_and_break_dax_layout() for dax files
who are going to be deduped. After that, call compare range function
only when files are both DAX or not.

Signed-off-by: Shiyang Ruan <ruansy.fnst@xxxxxxxxxxx>
Reviewed-by: Darrick J. Wong <djwong@xxxxxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
---
fs/xfs/xfs_file.c | 2 +-
fs/xfs/xfs_inode.c | 80 +++++++++++++++++++++++++++++++++++++++++---
fs/xfs/xfs_inode.h | 1 +
fs/xfs/xfs_reflink.c | 4 +--
4 files changed, 80 insertions(+), 7 deletions(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 2ef1930374d2..c3061723613c 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -846,7 +846,7 @@ xfs_wait_dax_page(
xfs_ilock(ip, XFS_MMAPLOCK_EXCL);
}
-static int
+int
xfs_break_dax_layouts(
struct inode *inode,
bool *retry)
diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index a4f6f034fb81..bdc084cdbf46 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -3790,6 +3790,61 @@ xfs_iolock_two_inodes_and_break_layout(
return 0;
}
+static int
+xfs_mmaplock_two_inodes_and_break_dax_layout(
+ struct xfs_inode *ip1,
+ struct xfs_inode *ip2)
+{
+ int error, attempts = 0;
+ bool retry;
+ struct page *page;
+ struct xfs_log_item *lp;
+
+ if (ip1->i_ino > ip2->i_ino)
+ swap(ip1, ip2);
+
+again:
+ retry = false;
+ /* Lock the first inode */
+ xfs_ilock(ip1, XFS_MMAPLOCK_EXCL);
+ error = xfs_break_dax_layouts(VFS_I(ip1), &retry);
+ if (error || retry) {
+ xfs_iunlock(ip1, XFS_MMAPLOCK_EXCL);
+ if (error == 0 && retry)
+ goto again;
+ return error;
+ }
+
+ if (ip1 == ip2)
+ return 0;
+
+ /* Nested lock the second inode */
+ lp = &ip1->i_itemp->ili_item;
+ if (lp && test_bit(XFS_LI_IN_AIL, &lp->li_flags)) {
+ if (!xfs_ilock_nowait(ip2,
+ xfs_lock_inumorder(XFS_MMAPLOCK_EXCL, 1))) {
+ xfs_iunlock(ip1, XFS_MMAPLOCK_EXCL);
+ if ((++attempts % 5) == 0)
+ delay(1); /* Don't just spin the CPU */
+ goto again;
+ }

I suspect we don't need this part for grabbing the MMAPLOCK^W pagecache
invalidatelock. The AIL only grabs the ILOCK, never the IOLOCK or the
MMAPLOCK.

Maybe I have misunderstood this part.

What I want is to lock the two inode nestedly. This code is copied from xfs_lock_two_inodes(), which checks this AIL during locking two inode with each of the three kinds of locks.

But I also found the recent merged function: filemap_invalidate_lock_two() just locks two inode directly without checking AIL. So, I am not if the AIL check is needed in this case.


+ } else
+ xfs_ilock(ip2, xfs_lock_inumorder(XFS_MMAPLOCK_EXCL, 1));
+ /*
+ * We cannot use xfs_break_dax_layouts() directly here because it may
+ * need to unlock & lock the XFS_MMAPLOCK_EXCL which is not suitable
+ * for this nested lock case.
+ */
+ page = dax_layout_busy_page(VFS_I(ip2)->i_mapping);
+ if (page && page_ref_count(page) != 1) {

Do you think the patch "ext4/xfs: add page refcount helper" would be a
good cleanup to head this series?

https://lore.kernel.org/linux-xfs/20210913161604.31981-1-alex.sierra@xxxxxxx/T/#m59cf7cd5c0d521ad487fa3a15d31c3865db88bdf

Got it.


--
Thanks,
Ruan


The rest of the logic looks ok.

--D

+ xfs_iunlock(ip2, XFS_MMAPLOCK_EXCL);
+ xfs_iunlock(ip1, XFS_MMAPLOCK_EXCL);
+ goto again;
+ }
+
+ return 0;
+}
+
/*
* Lock two inodes so that userspace cannot initiate I/O via file syscalls or
* mmap activity.
@@ -3804,8 +3859,19 @@ xfs_ilock2_io_mmap(
ret = xfs_iolock_two_inodes_and_break_layout(VFS_I(ip1), VFS_I(ip2));
if (ret)
return ret;
- filemap_invalidate_lock_two(VFS_I(ip1)->i_mapping,
- VFS_I(ip2)->i_mapping);
+
+ if (IS_DAX(VFS_I(ip1)) && IS_DAX(VFS_I(ip2))) {
+ ret = xfs_mmaplock_two_inodes_and_break_dax_layout(ip1, ip2);
+ if (ret) {
+ inode_unlock(VFS_I(ip2));
+ if (ip1 != ip2)
+ inode_unlock(VFS_I(ip1));
+ return ret;
+ }
+ } else
+ filemap_invalidate_lock_two(VFS_I(ip1)->i_mapping,
+ VFS_I(ip2)->i_mapping);
+
return 0;
}
@@ -3815,8 +3881,14 @@ xfs_iunlock2_io_mmap(
struct xfs_inode *ip1,
struct xfs_inode *ip2)
{
- filemap_invalidate_unlock_two(VFS_I(ip1)->i_mapping,
- VFS_I(ip2)->i_mapping);
+ if (IS_DAX(VFS_I(ip1)) && IS_DAX(VFS_I(ip2))) {
+ xfs_iunlock(ip2, XFS_MMAPLOCK_EXCL);
+ if (ip1 != ip2)
+ xfs_iunlock(ip1, XFS_MMAPLOCK_EXCL);
+ } else
+ filemap_invalidate_unlock_two(VFS_I(ip1)->i_mapping,
+ VFS_I(ip2)->i_mapping);
+
inode_unlock(VFS_I(ip2));
if (ip1 != ip2)
inode_unlock(VFS_I(ip1));
diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
index b21b177832d1..f7e26fe31a26 100644
--- a/fs/xfs/xfs_inode.h
+++ b/fs/xfs/xfs_inode.h
@@ -472,6 +472,7 @@ enum xfs_prealloc_flags {
int xfs_update_prealloc_flags(struct xfs_inode *ip,
enum xfs_prealloc_flags flags);
+int xfs_break_dax_layouts(struct inode *inode, bool *retry);
int xfs_break_layouts(struct inode *inode, uint *iolock,
enum layout_break_reason reason);
diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
index 9d876e268734..3b99c9dfcf0d 100644
--- a/fs/xfs/xfs_reflink.c
+++ b/fs/xfs/xfs_reflink.c
@@ -1327,8 +1327,8 @@ 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))
--
2.33.0