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

[Brian Foster <bfoster@redhat.com>]

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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