On Tue, Apr 24, 2018 at 04:33:50PM -0700, Dan Williams wrote: > xfs_break_dax_layouts(), similar to xfs_break_leased_layouts(), scans > for busy / pinned dax pages and waits for those pages to go idle before > any potential extent unmap operation. > > dax_layout_busy_page() handles synchronizing against new page-busy > events (get_user_pages). It invalidates all mappings to trigger the > get_user_pages slow path which will eventually block on the xfs inode > lock held in XFS_MMAPLOCK_EXCL mode. If dax_layout_busy_page() finds a > busy page it returns it for xfs to wait for the page-idle event that > will fire when the page reference count reaches 1 (recall ZONE_DEVICE > pages are idle at count 1, see generic_dax_pagefree()). > > While waiting, the XFS_MMAPLOCK_EXCL lock is dropped in order to not > deadlock the process that might be trying to elevate the page count of > more pages before arranging for any of them to go idle. I.e. the typical > case of submitting I/O is that iov_iter_get_pages() elevates the > reference count of all pages in the I/O before starting I/O on the first > page. The process of elevating the reference count of all pages involved > in an I/O may cause faults that need to take XFS_MMAPLOCK_EXCL. > > Although XFS_MMAPLOCK_EXCL is dropped while waiting, XFS_IOLOCK_EXCL is > held while sleeping. We need this to prevent starvation of the truncate > path as continuous submission of direct-I/O could starve the truncate > path indefinitely if the lock is dropped. > > Cc: Dave Chinner <[email protected]> > Cc: "Darrick J. Wong" <[email protected]> > Cc: Ross Zwisler <[email protected]> > Reported-by: Jan Kara <[email protected]> > Cc: Christoph Hellwig <[email protected]> > Signed-off-by: Dan Williams <[email protected]>
I should've acked this explicitly since it's xfs code, Acked-by: Darrick J. Wong <[email protected]> The rest of it looks fine enough to me too, but there's no Acked-by-goober tag to put on them. :P --D > --- > fs/xfs/xfs_file.c | 59 > +++++++++++++++++++++++++++++++++++++++++++---------- > 1 file changed, 48 insertions(+), 11 deletions(-) > > diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c > index 1a5176b21803..4e98d0dcc035 100644 > --- a/fs/xfs/xfs_file.c > +++ b/fs/xfs/xfs_file.c > @@ -718,6 +718,37 @@ xfs_file_write_iter( > return ret; > } > > +static void > +xfs_wait_dax_page( > + struct inode *inode, > + bool *did_unlock) > +{ > + struct xfs_inode *ip = XFS_I(inode); > + > + *did_unlock = true; > + xfs_iunlock(ip, XFS_MMAPLOCK_EXCL); > + schedule(); > + xfs_ilock(ip, XFS_MMAPLOCK_EXCL); > +} > + > +static int > +xfs_break_dax_layouts( > + struct inode *inode, > + uint iolock, > + bool *did_unlock) > +{ > + struct page *page; > + > + *did_unlock = false; > + page = dax_layout_busy_page(inode->i_mapping); > + if (!page) > + return 0; > + > + return ___wait_var_event(&page->_refcount, > + atomic_read(&page->_refcount) == 1, TASK_INTERRUPTIBLE, > + 0, 0, xfs_wait_dax_page(inode, did_unlock)); > +} > + > int > xfs_break_layouts( > struct inode *inode, > @@ -729,17 +760,23 @@ xfs_break_layouts( > > ASSERT(xfs_isilocked(XFS_I(inode), XFS_IOLOCK_SHARED|XFS_IOLOCK_EXCL)); > > - switch (reason) { > - case BREAK_UNMAP: > - ASSERT(xfs_isilocked(XFS_I(inode), XFS_MMAPLOCK_EXCL)); > - /* fall through */ > - case BREAK_WRITE: > - error = xfs_break_leased_layouts(inode, iolock, &retry); > - break; > - default: > - WARN_ON_ONCE(1); > - return -EINVAL; > - } > + do { > + switch (reason) { > + case BREAK_UNMAP: > + ASSERT(xfs_isilocked(XFS_I(inode), XFS_MMAPLOCK_EXCL)); > + > + error = xfs_break_dax_layouts(inode, *iolock, &retry); > + /* fall through */ > + case BREAK_WRITE: > + if (error || retry) > + break; > + error = xfs_break_leased_layouts(inode, iolock, &retry); > + break; > + default: > + WARN_ON_ONCE(1); > + return -EINVAL; > + } > + } while (error == 0 && retry); > > return error; > } > > -- > To unsubscribe from this list: send the line "unsubscribe linux-xfs" in > the body of a message to [email protected] > More majordomo info at http://vger.kernel.org/majordomo-info.html _______________________________________________ Linux-nvdimm mailing list [email protected] https://lists.01.org/mailman/listinfo/linux-nvdimm
