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Message-ID: <20210916041811.GB34874@magnolia>
Date: Wed, 15 Sep 2021 21:18:11 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: Shiyang Ruan <ruansy.fnst@...itsu.com>
Cc: hch@....de, linux-xfs@...r.kernel.org, dan.j.williams@...el.com,
david@...morbit.com, linux-fsdevel@...r.kernel.org,
linux-kernel@...r.kernel.org, nvdimm@...ts.linux.dev,
rgoldwyn@...e.de, viro@...iv.linux.org.uk, willy@...radead.org
Subject: Re: [PATCH v9 8/8] xfs: Add dax dedupe support
On Thu, Sep 16, 2021 at 12:01:18PM +0800, Shiyang Ruan wrote:
>
>
> 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@...itsu.com>
> > > Reviewed-by: Darrick J. Wong <djwong@...nel.org>
> > > Reviewed-by: Christoph Hellwig <hch@....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.
>
> 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.
<nod> It's totally reasonable to copy-paste the function you want and
change it as needed...
> 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.
...especially when even the maintainer is only 99% sure that the AIL
checking chunk here can be removed. Anyone else have an opinion?
--D
> >
> > > + } 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
>
> 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
> > >
> > >
> > >
>
>
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