Re: [PATCH 15/20] xfs: add an extent to the rmap btree

Brian Foster
2015-06-25T16:41:27Z

On Wed, Jun 03, 2015 at 04:04:52PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> Now all the btree, free space and transaction infrastructure is in
> place, we can finally add the code to insert reverse mappings to the
> rmap btree. Freeing will be done in a spearate patch, so just the
> addition operation can be focussed on here.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
> fs/xfs/libxfs/xfs_rmap.c | 139 ++++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 138 insertions(+), 1 deletion(-)
>
> diff --git a/fs/xfs/libxfs/xfs_rmap.c b/fs/xfs/libxfs/xfs_rmap.c
> index 38a92a1..c1e5d23 100644
> --- a/fs/xfs/libxfs/xfs_rmap.c
> +++ b/fs/xfs/libxfs/xfs_rmap.c
> @@ -120,6 +120,18 @@ out_error:
> return error;
> }
>
> +/*
> + * When we allocate a new block, the first thing we do is add a reference to the
> + * extent in the rmap btree. This takes the form of a [agbno, length, owner]
> + * record. Newly inserted extents should never overlap with an existing extent
> + * in the rmap btree. Hence the insertion is a relatively trivial exercise,
> + * involving checking for adjacent records and merging if the new extent is
> + * contiguous and has the same owner.
> + *
> + * Note that we have no MAXEXTLEN limits here when merging as the length in the
> + * record has the full 32 bits available and hence a single record can track the
> + * entire space in the AG.
> + */
> int
> xfs_rmap_alloc(
> struct xfs_trans *tp,
> @@ -130,18 +142,143 @@ xfs_rmap_alloc(
> uint64_t owner)
> {
> struct xfs_mount *mp = tp->t_mountp;
> + struct xfs_btree_cur *cur;
> + struct xfs_rmap_irec ltrec;
> + struct xfs_rmap_irec gtrec;
> + int have_gt;
> int error = 0;
> + int i;
>
> if (!xfs_sb_version_hasrmapbt(&mp->m_sb))
> return 0;
>
> trace_xfs_rmap_alloc_extent(mp, agno, bno, len, owner);
> - if (1)
> + cur = xfs_rmapbt_init_cursor(mp, tp, agbp, agno);
> +
> + /*
> + * For the initial lookup, look for and exact match or the left-adjacent
> + * record for our insertion point. This will also give us the record for
> + * start block contiguity tests.
> + */
> + error = xfs_rmap_lookup_le(cur, bno, len, owner, &i);
> + if (error)
> + goto out_error;
> + XFS_WANT_CORRUPTED_GOTO(mp, i == 1, out_error);
> +

Are we intentionally relying on the fact that a left record will always
exist due to the static metadata blocks that start the AG? If so, I'd
just suggest to note that in the comment above.

Brian

> + error = xfs_rmap_get_rec(cur, &ltrec, &i);
> + if (error)
> goto out_error;
> + XFS_WANT_CORRUPTED_GOTO(mp, i == 1, out_error);
> + //printk("rmalloc ag %d bno 0x%x/0x%x/0x%llx, ltrec 0x%x/0x%x/0x%llx\n",
> + // agno, bno, len, owner, ltrec.rm_startblock,
> + // ltrec.rm_blockcount, ltrec.rm_owner);
> +
> + XFS_WANT_CORRUPTED_GOTO(mp,
> + ltrec.rm_startblock + ltrec.rm_blockcount <= bno, out_error);
> +
> + /*
> + * Increment the cursor to see if we have a right-adjacent record to our
> + * insertion point. This will give us the record for end block
> + * contiguity tests.
> + */
> + error = xfs_btree_increment(cur, 0, &have_gt);
> + if (error)
> + goto out_error;
> + if (have_gt) {
> + error = xfs_rmap_get_rec(cur, &gtrec, &i);
> + if (error)
> + goto out_error;
> + XFS_WANT_CORRUPTED_GOTO(mp, i == 1, out_error);
> + //printk("rmalloc ag %d bno 0x%x/0x%x/0x%llx, gtrec 0x%x/0x%x/0x%llx\n",
> + // agno, bno, len, owner, gtrec.rm_startblock,
> + // gtrec.rm_blockcount, gtrec.rm_owner);
> + XFS_WANT_CORRUPTED_GOTO(mp, bno + len <= gtrec.rm_startblock,
> + out_error);
> + } else {
> + gtrec.rm_owner = XFS_RMAP_OWN_NULL;
> + }
> +
> + /*
> + * Note: cursor currently points one record to the right of ltrec, even
> + * if there is no record in the tree to the right.
> + */
> + if (ltrec.rm_owner == owner &&
> + ltrec.rm_startblock + ltrec.rm_blockcount == bno) {
> + /*
> + * left edge contiguous, merge into left record.
> + *
> + * ltbno ltlen
> + * orig: |ooooooooo|
> + * adding: |aaaaaaaaa|
> + * result: |rrrrrrrrrrrrrrrrrrr|
> + * bno len
> + */
> + //printk("add left\n");
> + ltrec.rm_blockcount += len;
> + if (gtrec.rm_owner == owner &&
> + bno + len == gtrec.rm_startblock) {
> + //printk("add middle\n");
> + /*
> + * right edge also contiguous, delete right record
> + * and merge into left record.
> + *
> + * ltbno ltlen gtbno gtlen
> + * orig: |ooooooooo| |ooooooooo|
> + * adding: |aaaaaaaaa|
> + * result: |rrrrrrrrrrrrrrrrrrrrrrrrrrrrr|
> + */
> + ltrec.rm_blockcount += gtrec.rm_blockcount;
> + error = xfs_btree_delete(cur, &i);
> + if (error)
> + goto out_error;
> + XFS_WANT_CORRUPTED_GOTO(mp, i == 1, out_error);
> + }
> +
> + /* point the cursor back to the left record and update */
> + error = xfs_btree_decrement(cur, 0, &have_gt);
> + if (error)
> + goto out_error;
> + error = xfs_rmap_update(cur, &ltrec);
> + if (error)
> + goto out_error;
> + } else if (gtrec.rm_owner == owner &&
> + bno + len == gtrec.rm_startblock) {
> + /*
> + * right edge contiguous, merge into right record.
> + *
> + * gtbno gtlen
> + * Orig: |ooooooooo|
> + * adding: |aaaaaaaaa|
> + * Result: |rrrrrrrrrrrrrrrrrrr|
> + * bno len
> + */
> + //printk("add right\n");
> + gtrec.rm_startblock = bno;
> + gtrec.rm_blockcount += len;
> + error = xfs_rmap_update(cur, &gtrec);
> + if (error)
> + goto out_error;
> + } else {
> + //printk("add no match\n");
> + /*
> + * no contiguous edge with identical owner, insert
> + * new record at current cursor position.
> + */
> + cur->bc_rec.r.rm_startblock = bno;
> + cur->bc_rec.r.rm_blockcount = len;
> + cur->bc_rec.r.rm_owner = owner;
> + error = xfs_btree_insert(cur, &i);
> + if (error)
> + goto out_error;
> + XFS_WANT_CORRUPTED_GOTO(mp, i == 1, out_error);
> + }
> +
> trace_xfs_rmap_alloc_extent_done(mp, agno, bno, len, owner);
> + xfs_btree_del_cursor(cur, XFS_BTREE_NOERROR);
> return 0;
>
> out_error:
> trace_xfs_rmap_alloc_extent_error(mp, agno, bno, len, owner);
> + xfs_btree_del_cursor(cur, XFS_BTREE_ERROR);
> return error;
> }
> --
> 2.0.0
>
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