Re: [PATCH RFC 2/2] xfs: don't log dirty ranges for ordered buffers

Brian Foster
2017-08-17T11:06:39Z

On Wed, Aug 16, 2017 at 10:15:01AM -0700, Darrick J. Wong wrote:
> On Mon, Aug 14, 2017 at 12:54:51PM -0400, Brian Foster wrote:
> > Ordered buffers are attached to transactions and pushed through the
> > logging infrastructure just like normal buffers with the exception
> > that they are not actually written to the log. Therefore, we don't
> > need to log dirty ranges of ordered buffers. xfs_trans_log_buf() is
> > called on ordered buffers to set up all of the dirty state on the
> > transaction, buffer and log item and prepare the buffer for I/O.
> >
> > Now that xfs_trans_dirty_buf() is available, call it from
> > xfs_trans_ordered_buf() so the latter is now mutually exclusive with
> > xfs_trans_log_buf(). This reflects the implementation of ordered
> > buffers and helps eliminate confusion over the need to log ranges of
> > ordered buffers just to set up internal log state.
> >
> > Signed-off-by: Brian Foster <bfoster@redhat.com>
> > ---
> > fs/xfs/libxfs/xfs_btree.c | 3 ++-
> > fs/xfs/libxfs/xfs_ialloc.c | 2 --
> > fs/xfs/xfs_trans_buf.c | 25 +++++++++++++------------
> > 3 files changed, 15 insertions(+), 15 deletions(-)
> >
> > diff --git a/fs/xfs/libxfs/xfs_btree.c b/fs/xfs/libxfs/xfs_btree.c
> > index e0bcc4a..9c97896 100644
> > --- a/fs/xfs/libxfs/xfs_btree.c
> > +++ b/fs/xfs/libxfs/xfs_btree.c
> > @@ -4466,7 +4466,8 @@ xfs_btree_block_change_owner(
> > if (bp) {
> > if (cur->bc_tp) {
> > xfs_trans_ordered_buf(cur->bc_tp, bp);
> > - xfs_btree_log_block(cur, bp, XFS_BB_OWNER);
> > + /*xfs_trans_buf_set_type(cur->bc_tp, bp,
> > + XFS_BLFT_BTREE_BUF);*/
>
> I don't see the point of this, but maybe you've already dropped it anyway. :)
>

Yes, it's been dropped. I had it there to remind myself to look further
into it because it looked like the only part of xfs_btree_log_block()
that could have any effect on an ordered buffer.

> > } else {
> > xfs_buf_delwri_queue(bp, bbcoi->buffer_list);
> > }
> > diff --git a/fs/xfs/libxfs/xfs_ialloc.c b/fs/xfs/libxfs/xfs_ialloc.c
> > index ffd5a15..12c0452 100644
> > --- a/fs/xfs/libxfs/xfs_ialloc.c
> > +++ b/fs/xfs/libxfs/xfs_ialloc.c
> > @@ -378,8 +378,6 @@ xfs_ialloc_inode_init(
> > * transaction and pin the log appropriately.
> > */
> > xfs_trans_ordered_buf(tp, fbuf);
> > - xfs_trans_log_buf(tp, fbuf, 0,
> > - BBTOB(fbuf->b_length) - 1);
> > }
> > } else {
> > fbuf->b_flags |= XBF_DONE;
> > diff --git a/fs/xfs/xfs_trans_buf.c b/fs/xfs/xfs_trans_buf.c
> > index 58818a0..3a358cb 100644
> > --- a/fs/xfs/xfs_trans_buf.c
> > +++ b/fs/xfs/xfs_trans_buf.c
> > @@ -560,16 +560,12 @@ xfs_trans_log_buf(
> > struct xfs_buf_log_item *bip = bp->b_fspriv;
> >
> > ASSERT(first <= last && last < BBTOB(bp->b_length));
> > + ASSERT(!(bip->bli_flags & XFS_BLI_ORDERED));
> >
> > xfs_trans_dirty_buf(tp, bp);
> >
> > - /*
> > - * If we have an ordered buffer we are not logging any dirty range but
> > - * it still needs to be marked dirty and that it has been logged.
> > - */
> > trace_xfs_trans_log_buf(bip);
> > - if (!(bip->bli_flags & XFS_BLI_ORDERED))
> > - xfs_buf_item_log(bip, first, last);
> > + xfs_buf_item_log(bip, first, last);
> > }
> >
> >
> > @@ -722,12 +718,11 @@ xfs_trans_inode_alloc_buf(
> > }
> >
> > /*
> > - * Mark the buffer as ordered for this transaction. This means
> > - * that the contents of the buffer are not recorded in the transaction
> > - * but it is tracked in the AIL as though it was. This allows us
> > - * to record logical changes in transactions rather than the physical
> > - * changes we make to the buffer without changing writeback ordering
> > - * constraints of metadata buffers.
> > + * Mark the buffer as ordered for this transaction. This means that the contents
> > + * of the buffer are not recorded in the transaction but it is tracked in the
> > + * AIL as though it was. This allows us to record logical changes in
> > + * transactions rather than the physical changes we make to the buffer without
> > + * changing writeback ordering constraints of metadata buffers.
>
> Did the text of this comment change? AFAICT the only difference is
> where we line wrap?
>
> (If that's the case, why bother?)
>

The text hasn't changed. This just fixes the wrapping to 80 chars, which
is just one of those things I tend to fix up when already making changes
in a particular function (along with similar cleanups to code
indentation, eliminating the old typedef usages, etc.).

> > */
> > void
> > xfs_trans_ordered_buf(
> > @@ -742,6 +737,12 @@ xfs_trans_ordered_buf(
> >
> > bip->bli_flags |= XFS_BLI_ORDERED;
> > trace_xfs_buf_item_ordered(bip);
> > +
> > + /*
> > + * We don't log a dirty range of an ordered buffer but it still needs
> > + * to be marked dirty and that it has been logged.
> > + */
> > + xfs_trans_dirty_buf(tp, bp);
>
> Otherwise looks ok to me...
>

Thanks..

Brian

> --D
>
> > }
> >
> > /*
> > --
> > 2.9.4
> >
> > --
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