[PATCH 1/2] docs: fix a typo in the AGF section of the disk format doc

[PATCH 1/2] docs: fix a typo in the AGF section of the disk format doc

[Darrick J. Wong]

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
 .../allocation_groups.asciidoc                     |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)


diff --git a/design/XFS_Filesystem_Structure/allocation_groups.asciidoc b/design/XFS_Filesystem_Structure/allocation_groups.asciidoc
index 38d7357..51ca57d 100644
--- a/design/XFS_Filesystem_Structure/allocation_groups.asciidoc
+++ b/design/XFS_Filesystem_Structure/allocation_groups.asciidoc
@@ -636,7 +636,7 @@ The size of the reference count B+tree in this allocation group, in blocks.
 *agf_refcount_root*::
 Block number for the root of the reference count B+tree, if enabled.
 
-*agf_refcount_root*::
+*agf_refcount_level*::
 Depth of the reference count B+tree, if enabled.
 
 *agf_spare64*::

[PATCH 2/2] docs: update refcount btree to reflect new cow staging extent policy

[Darrick J. Wong]

We now record the extents being used to stage a copy on write operation
in the refcount btree with the high bit of rc_startblock set and a
reference count of 1.  Setting the high bit helps us reduce CoW GC time
at mount by moving all the records to the right side of the tree.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
 .../XFS_Filesystem_Structure/refcountbt.asciidoc   |   19 ++++++++++++++-----
 1 file changed, 14 insertions(+), 5 deletions(-)


diff --git a/design/XFS_Filesystem_Structure/refcountbt.asciidoc b/design/XFS_Filesystem_Structure/refcountbt.asciidoc
index dbbb98e..508a9dd 100644
--- a/design/XFS_Filesystem_Structure/refcountbt.asciidoc
+++ b/design/XFS_Filesystem_Structure/refcountbt.asciidoc
@@ -25,7 +25,10 @@ struct xfs_refcount_rec {
 ----
 
 *rc_startblock*::
-AG block number of this record.
+AG block number of this record.  The high bit is set for all records
+referring to an extent that is being used to stage a copy on write
+operation.  This reduces recovery time during mount operations.  The
+reference count of these staging events must only be 1.
 
 *rc_blockcount*::
 The length of this extent.
@@ -81,12 +84,18 @@ lsn = 0x200004ec2
 uuid = f1f89746-e00b-49c9-96b3-ecef0f2f14ae
 owner = 0
 crc = 0xc3962813 (correct)
-recs[1-80] = [startblock,blockcount,refcount]
-        1:[65780,1,2] 2:[65781,1,3] 3:[65785,2,2] 4:[66640,1,2]
-        5:[69602,4,2] 6:[72256,16,2] 7:[72871,4,2] 8:[72879,20,2]
-        9:[73395,4,2] 10:[75063,4,2] 11:[79093,4,2] 12:[86344,16,2]
+recs[1-80] = [startblock,blockcount,refcount,cowflag]
+        1:[65780,1,2,0] 2:[65781,1,3,0] 3:[65785,2,2,0] 4:[66640,1,2,0]
+        5:[69602,4,2,0] 6:[72256,16,2,0] 7:[72871,4,2,0] 8:[72879,20,2,0]
+        9:[73395,4,2,0] 10:[75063,4,2,0] 11:[79093,4,2,0] 12:[86344,16,2,0]
+        ...
+        80:[35235,10,1,1]
 ----
 
+Notice record 80.  The copy on write flag is set and the reference count is
+1, which indicates that the extent 35,235 - 35,244 are being used to stage a
+copy on write activity.  The "cowflag" field is the high bit of rc_startblock.
+
 Record 6 in the reference count B+tree for AG 0 indicates that the AG extent
 starting at block 72,256 and running for 16 blocks has a reference count of 2.
 This means that there are two files sharing the block:

Re: [PATCH 1/2] docs: fix a typo in the AGF section of the disk format doc

[Christoph Hellwig]

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH 2/2] docs: update refcount btree to reflect new cow staging extent policy

[Christoph Hellwig]

Looks good,

Reviewed-by: Christoph Hellwig <hch@lst.de>