linux-ext4 - [PATCH 03/33] ext/052: use popdir.pl for much faster directory creation

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Message-ID: <176169820032.1433624.6179702780762580279.stgit@frogsfrogsfrogs>
Date: Tue, 28 Oct 2025 18:21:12 -0700
From: "Darrick J. Wong" <djwong@...nel.org>
To: djwong@...nel.org, zlang@...hat.com
Cc: neal@...pa.dev, fstests@...r.kernel.org, linux-ext4@...r.kernel.org,
 linux-fsdevel@...r.kernel.org, joannelkoong@...il.com, bernd@...ernd.com
Subject: [PATCH 03/33] ext/052: use popdir.pl for much faster directory
 creation

From: Darrick J. Wong <djwong@...nel.org>

This program wants to create a large directory htree index, and it
doesn't care what the children are.  Reduce the runtime of this program
by 2/3 by using hardlinks when possible instead of allocating 400,000
new child files.  This is an even bigger win for fuse2fs, which has a
runtime of 6.5h.

Signed-off-by: "Darrick J. Wong" <djwong@...nel.org>
---
 src/popdir.pl  |    9 ++++++++-
 tests/ext4/052 |    4 +++-
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/src/popdir.pl b/src/popdir.pl
index 0104957a3c941e..251500c2255f33 100755
--- a/src/popdir.pl
+++ b/src/popdir.pl
@@ -72,7 +72,14 @@ for ($i = $start; $i <= $end; $i += $incr) {
 	} elsif ($hardlink && $i > $start) {
 		# hardlink everything after the first file
 		$verbose && print "ln $link_fname $fname\n";
-		link $link_fname, $fname;
+		if (not link $link_fname, $fname) {
+			# if hardlink fails, create a new file in case the old
+			# file reached maximum link count
+			$verbose && print "touch $fname\n";
+			open(DONTCARE, ">$fname") or die("touch $fname");
+			close(DONTCARE);
+			$link_fname = $fname;
+		}
 	} elsif (($i % 100) < $file_pct) {
 		# create a file
 		$verbose && print "touch $fname\n";
diff --git a/tests/ext4/052 b/tests/ext4/052
index 0df8a651383ec7..18b2599f43c7ba 100755
--- a/tests/ext4/052
+++ b/tests/ext4/052
@@ -56,7 +56,9 @@ mkdir -p $loop_mnt
 _mount -o loop $fs_img $loop_mnt > /dev/null  2>&1 || \
 	_fail "Couldn't do initial mount"

-if ! $here/src/dirstress -c -d $loop_mnt -p 1 -f 400000 -C >$tmp.out 2>&1
+# popdir.pl is much faster than creating 400k file with dirstress
+mkdir "${loop_mnt}/stress.0"
+if ! $here/src/popdir.pl --dir "${loop_mnt}/stress.0" --end 400000 --hardlink --format "XXXXXXXXXXXX.%ld" > $tmp.out 2>&1
 then
     echo "    dirstress failed"
     cat $tmp.out >> $seqres.full