| Message ID | 1480971924-4864-2-git-send-email-hch@lst.de (mailing list archive) |
|---|---|
| State | Superseded, archived |
| Headers | show |
On Mon, Dec 05, 2016 at 10:05:22PM +0100, Christoph Hellwig wrote: > We currently fall back from direct to buffered writes if we detect a > remaining shared extent in the iomap_begin callback. But by the time > iomap_begin is called for the potentially unaligned end block we might > have already written most of the data to disk, which we'd now write > again using buffered I/O. To avoid this reject all writes to reflinked > files before starting I/O so that we are guaranteed to only write the > data once. > > The alternative would be to unshare the unaligned start and/or end block > before doing the I/O. I think that's doable, and will actually be > required to support reflinks on DAX file system. But it will take a > little more time and I'd rather get rid of the double write ASAP. > > Signed-off-by: Christoph Hellwig <hch@lst.de> > --- Reviewed-by: Brian Foster <bfoster@redhat.com> > fs/xfs/xfs_file.c | 7 +++++++ > fs/xfs/xfs_iomap.c | 12 +----------- > 2 files changed, 8 insertions(+), 11 deletions(-) > > diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c > index f5effa6..873cd42 100644 > --- a/fs/xfs/xfs_file.c > +++ b/fs/xfs/xfs_file.c > @@ -532,6 +532,13 @@ xfs_file_dio_aio_write( > if ((iocb->ki_pos & mp->m_blockmask) || > ((iocb->ki_pos + count) & mp->m_blockmask)) { > unaligned_io = 1; > + > + /* > + * We can't properly handle unaligned direct I/O to reflink > + * files yet, as we can't unshare a partial block. > + */ > + if (xfs_is_reflink_inode(ip)) > + return -EREMCHG; > iolock = XFS_IOLOCK_EXCL; > } else { > iolock = XFS_IOLOCK_SHARED; > diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c > index 0d14742..78105db 100644 > --- a/fs/xfs/xfs_iomap.c > +++ b/fs/xfs/xfs_iomap.c > @@ -1026,17 +1026,7 @@ xfs_file_iomap_begin( > if (error) > goto out_unlock; > > - /* > - * We're here because we're trying to do a directio write to a > - * region that isn't aligned to a filesystem block. If the > - * extent is shared, fall back to buffered mode to handle the > - * RMW. > - */ > - if (!(flags & IOMAP_REPORT) && shared) { > - trace_xfs_reflink_bounce_dio_write(ip, &imap); > - error = -EREMCHG; > - goto out_unlock; > - } > + ASSERT((flags & IOMAP_REPORT) || !shared); > } > > if ((flags & (IOMAP_WRITE | IOMAP_ZERO)) && xfs_is_reflink_inode(ip)) { > -- > 2.1.4 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-xfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c index f5effa6..873cd42 100644 --- a/fs/xfs/xfs_file.c +++ b/fs/xfs/xfs_file.c @@ -532,6 +532,13 @@ xfs_file_dio_aio_write( if ((iocb->ki_pos & mp->m_blockmask) || ((iocb->ki_pos + count) & mp->m_blockmask)) { unaligned_io = 1; + + /* + * We can't properly handle unaligned direct I/O to reflink + * files yet, as we can't unshare a partial block. + */ + if (xfs_is_reflink_inode(ip)) + return -EREMCHG; iolock = XFS_IOLOCK_EXCL; } else { iolock = XFS_IOLOCK_SHARED; diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c index 0d14742..78105db 100644 --- a/fs/xfs/xfs_iomap.c +++ b/fs/xfs/xfs_iomap.c @@ -1026,17 +1026,7 @@ xfs_file_iomap_begin( if (error) goto out_unlock; - /* - * We're here because we're trying to do a directio write to a - * region that isn't aligned to a filesystem block. If the - * extent is shared, fall back to buffered mode to handle the - * RMW. - */ - if (!(flags & IOMAP_REPORT) && shared) { - trace_xfs_reflink_bounce_dio_write(ip, &imap); - error = -EREMCHG; - goto out_unlock; - } + ASSERT((flags & IOMAP_REPORT) || !shared); } if ((flags & (IOMAP_WRITE | IOMAP_ZERO)) && xfs_is_reflink_inode(ip)) {
We currently fall back from direct to buffered writes if we detect a remaining shared extent in the iomap_begin callback. But by the time iomap_begin is called for the potentially unaligned end block we might have already written most of the data to disk, which we'd now write again using buffered I/O. To avoid this reject all writes to reflinked files before starting I/O so that we are guaranteed to only write the data once. The alternative would be to unshare the unaligned start and/or end block before doing the I/O. I think that's doable, and will actually be required to support reflinks on DAX file system. But it will take a little more time and I'd rather get rid of the double write ASAP. Signed-off-by: Christoph Hellwig <hch@lst.de> --- fs/xfs/xfs_file.c | 7 +++++++ fs/xfs/xfs_iomap.c | 12 +----------- 2 files changed, 8 insertions(+), 11 deletions(-)