[08/34] common/populate: correct the parent pointer name creation formulae

Commit Message

Darrick J. Wong Feb. 4, 2025, 9:24 p.m. UTC

From: Darrick J. Wong <[e-mail]>

The formulae used to compute the number of parent pointers that we have
to create in a child file in order to generate a particular xattr
structure are not even close to correct -- the first one needs a bit of
adjustment, but the second one is way off and creates far too many
files.

Fix the computation, and document where the magic numbers come from.

Cc: <[e-mail]> # v2024.06.27
Fixes: 0c02207d61af9a ("populate: create hardlinks for parent pointers")
Signed-off-by: "Darrick J. Wong" <[e-mail]>
---
 common/populate |   13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

Patch

diff --git a/common/populate b/common/populate
index 4cf9c0691956a3..c907e04efd0ea9 100644
--- a/common/populate
+++ b/common/populate
@@ -473,13 +473,18 @@  _scratch_xfs_populate() {
 		__populate_create_dir "${SCRATCH_MNT}/PPTRS" 1 '' \
 			--hardlink --format "two_%d"
 
-		# Create one xattr leaf block of parent pointers
-		nr="$((blksz * 2 / 16))"
+		# Create one xattr leaf block of parent pointers.  The name is
+		# 8 bytes and, the handle is 12 bytes, which rounds up to 24
+		# bytes per record, plus xattr structure overhead.
+		nr="$((blksz / 24))"
 		__populate_create_dir "${SCRATCH_MNT}/PPTRS" ${nr} '' \
 			--hardlink --format "many%04d"
 
-		# Create multiple xattr leaf blocks of large parent pointers
-		nr="$((blksz * 16 / 16))"
+		# Create multiple xattr leaf blocks of large parent pointers.
+		# The name is 256 bytes and the handle is 12 bytes, which
+		# rounds up to 272 bytes per record, plus xattr structure
+		# overhead.
+		nr="$((blksz * 2 / 272))"
 		__populate_create_dir "${SCRATCH_MNT}/PPTRS" ${nr} '' \
 			--hardlink --format "y%0254d"