cc linux-xfs
On Tue, Nov 21, 2017 at 10:51:10AM -0600, Mark Tinguely wrote:
> On 11/21/2017 09:05 AM, Brian Foster wrote:
> > I ended up looking at tr_ifree while investigating some options to
> > resolve this problem and am slightly confused by the reservation
> > calculation. In particular, we do this for the inobt portion of the
> > operation (i.e., "the inode btree: max depth * blocksize"):
> >
> > xfs_calc_buf_res(2 + mp->m_ialloc_blks +
> > mp->m_in_maxlevels, 0) +
>
Hi Mark,
> I reviewed the Jeff Lui refactoring of the log space calculation years
> ago....
>
> There is some combination of entries only difference that I see is that the
> original calculation used the generic btree calculation for the inode btree
> and the generic btree calculation accounts for the by-block and by-count, so
> they are times two:
>
> /*
> * In freeing an inode we can modify:
> * the inode being freed: inode size
> * the super block free inode counter: sector size
> * the agi hash list and counters: sector size
> * the inode btree entry: block size
> * the on disk inode before ours in the agi hash list: inode cluster size
> * the inode btree: max depth * blocksize
> * the allocation btrees: 2 trees * (max depth - 1) * block size
> */
> STATIC uint
> xfs_calc_ifree_reservation(
> struct xfs_mount *mp)
> {
> return XFS_DQUOT_LOGRES(mp) +
> mp->m_sb.sb_inodesize +
> mp->m_sb.sb_sectsize +
> mp->m_sb.sb_sectsize +
> XFS_FSB_TO_B(mp, 1) +
> MAX((__uint16_t)XFS_FSB_TO_B(mp, 1),
> XFS_INODE_CLUSTER_SIZE(mp)) +
> 128 * 5 +
> XFS_ALLOCFREE_LOG_RES(mp, 1) +
> 128 * (2 + XFS_IALLOC_BLOCKS(mp) + mp->m_in_maxlevels +
> XFS_ALLOCFREE_LOG_COUNT(mp, 1));
> }
> ...
Indeed, this looks fairly similar to the line cited above from the
current code (modulo the xfs_calc_buf_res() refactoring). I'm curious
why we only consider the buffer overhead (i.e., 128 bytes *
->m_in_maxlevels) of the ->m_in_maxlevels value rather than the full
buffer size.
> /*
> * Per-extent log reservation for the allocation btree changes
> * involved in freeing or allocating an extent.
> * 2 trees * (2 blocks/level * max depth - 1) * block size
> */
> #define XFS_ALLOCFREE_LOG_RES(mp,nx) \
> ((nx) * (2 * XFS_FSB_TO_B((mp), 2 * XFS_AG_MAXLEVELS(mp) - 1)))
> #define XFS_ALLOCFREE_LOG_COUNT(mp,nx) \
> ((nx) * (2 * (2 * XFS_AG_MAXLEVELS(mp) - 1)))
>
> Doesn't the blocks for the btrees get allocated in:
>
> xfs_calc_buf_res(xfs_allocfree_log_count(mp, 1),
> XFS_FSB_TO_B(mp, 1)) +
Yeah, I believe that covers the log reservation for the allocation
btrees. I'm wondering if/where we'd account for a join of the inobt due
to freeing an inode chunk and removing the associated inobt record. I
suppose the above could also cover the inobt since the transaction is
rolled, but then aren't we assuming that m_in_maxlevels ==
m_ag_maxlevels..?
Brian
>
> And the rest of the calculation counts the log chunks that can get modified?
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