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    SubjectRe: [PATCH v9 8/8] xfs: Add dax dedupe support
    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@fujitsu.com>
    > Reviewed-by: Darrick J. Wong <djwong@kernel.org>
    > Reviewed-by: Christoph Hellwig <hch@lst.de>
    > ---
    > 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.

    > + } 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@amd.com/T/#m59cf7cd5c0d521ad487fa3a15d31c3865db88bdf

    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
    >
    >
    >

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