Re: [PATCH 2/5] libxfs: refactor the btree size calculator code

Dave Chinner
2016-02-12T01:07:55Z

On Thu, Feb 11, 2016 at 03:48:07PM -0800, Darrick J. Wong wrote:
> On Fri, Jan 22, 2016 at 04:35:08PM -0800, Darrick J. Wong wrote:
> > Create a macro to generate btree height calculator functions.
> > This will be used (much) later when we get to the refcount
> > btree.
> >
> > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > ---
> > libxfs/xfs_bmap.c | 18 +-----------------
> > libxfs/xfs_bmap_btree.c | 9 +++++++++
> > libxfs/xfs_bmap_btree.h | 3 +++
> > libxfs/xfs_btree.c | 28 ++++++++++++++++++++++++++++
> > libxfs/xfs_btree.h | 3 +++
> > 5 files changed, 44 insertions(+), 17 deletions(-)
> >
> >
> > diff --git a/libxfs/xfs_bmap.c b/libxfs/xfs_bmap.c
> > index aef7cf3..c134765 100644
> > --- a/libxfs/xfs_bmap.c
> > +++ b/libxfs/xfs_bmap.c
> > @@ -172,25 +172,9 @@ xfs_bmap_worst_indlen(
> > xfs_inode_t *ip, /* incore inode pointer */
> > xfs_filblks_t len) /* delayed extent length */
> > {
> > - int level; /* btree level number */
> > - int maxrecs; /* maximum record count at this level */
> > - xfs_mount_t *mp; /* mount structure */
> > xfs_filblks_t rval; /* return value */
> >
> > - mp = ip->i_mount;
> > - maxrecs = mp->m_bmap_dmxr[0];
> > - for (level = 0, rval = 0;
> > - level < XFS_BM_MAXLEVELS(mp, XFS_DATA_FORK);
> > - level++) {
> > - len += maxrecs - 1;
> > - do_div(len, maxrecs);
> > - rval += len;
> > - if (len == 1)
> > - return rval + XFS_BM_MAXLEVELS(mp, XFS_DATA_FORK) -
> > - level - 1;
> > - if (level == 0)
> > - maxrecs = mp->m_bmap_dmxr[1];
> > - }
> > + rval = xfs_bmbt_calc_size(ip->i_mount, len);
>
> NAK. This function figures out how many blocks could be required to handle
> adding (worst-case one-extent-per-block) extents to the bmbt and btree splits
> all the way up the tree, whereas xfs_btree_calc_size() merely calculates the
> number of blocks needed to create a tree with some number of records. When I
> start using the AG reservation code and counting the number of blocks in use at
> mount time, using the below xfs_btree_calc_size() to calculate the resevation
> size leads to undersized reservations, which (I think?) explains why I still
> occasionally run out of blocks when expanding the refcount tree, which is
> supposed to reserve /all/ the blocks it'll ever need.
>
> This function should go back to the way it was, and the xfs_btree_calc_size()
> function will get fixed to calculate tree size correctly.
>
> Also NAK on the kernelside version of this patch.

Thanks for the heads-up, Darrick. I hadn't pulled this in to either
tree yet, because it hadn't got a reviewed-by. I guess that's a sign
that the process is working as it should. :P

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com