From 93729d83fa5bf15f4ec694e08e9777bde858fb41 Mon Sep 17 00:00:00 2001
From: Lars Ellenberg <lars.ellenberg@linbit.com>
Date: Thu, 16 Oct 2025 10:58:37 +0200
Subject: [PATCH 1/2] Filesystem: speed up get_pids

With force_umount=safe, we "manually" scan the /proc/ file system.

We look for symlinks pointing into the path we are interested in.
Specifically, we are interested in
  /proc/<pid>/{root,exe,cwd}
  /proc/<pid>/fd/<fd>
We also look for relevant memory mappings in /proc/<pid>/maps

All these are per process, not per "task" or "thread".
see procfs(5) and pthreads(7).
Still, we currently also scan /proc/<pid>/task/<tid>/
for all the same things.

With a large system with many heavily threaded processes,
this can significantly slow down this scanning,
without gaining new information.

Adding -maxdepth to the find command line avoids this useless work,
potentially reducing the scanning time by orders of magnitute
on systems with many heavily threaded processes.

We could also write a dedicated helper in C to do the very same thing,
with the option to "short circuit" and proceed with the next pid
as soon as the first "match" is found for the currently inspected pid.

That could further reduce the scanning time
by about an additional factor of 10.
---
 heartbeat/Filesystem | 25 +++++++++++++++++++++----
 1 file changed, 21 insertions(+), 4 deletions(-)

diff --git a/heartbeat/Filesystem b/heartbeat/Filesystem
index 6d3960162..f76339fd6 100755
--- a/heartbeat/Filesystem
+++ b/heartbeat/Filesystem
@@ -680,14 +680,31 @@ get_pids()
 		# -path "/proc/[!0-9]*" -prune -o ...
 		# -path "/proc/[0-9]*" -a ...
 		# the latter seemd to be significantly faster for this one in my naive test.
+
+		# root, cwd, exe, maps, fd: all per process, not per task ("thread").
+		# -maxdepth to avoid repeatedly scanning the same thing
+		# for all threads of a heavily threaded process.
+		#
+		# Adding -maxdepth reduced scanning from > 16 seconds to < 2 seconds
+		# on a mostly idle system that happened to run a few java processes.
+		#
+		# We can also add a dedicated helper in C do twhat is done below,
+		# which would reduce the scanning time by an
+		# additional factor of 10 again.
+		#
+		# Or trust that fuser (above) learned something in the last 15 years
+		# and avoids blocking operations meanwhile?
 		procs=$(exec 2>/dev/null;
-			find /proc -path "/proc/[0-9]*" -type l \( -lname "${dir}/*" -o -lname "${dir}" \) -print |
+			find /proc -mindepth 1 -maxdepth 3 \
+				-path "/proc/[0-9]*" \
+				-type l \( -lname "${dir}/*" -o -lname "${dir}" \) -print |
 			awk -F/ '{print $3}' | uniq)
 
-		# This finds both /proc/<pid>/maps and /proc/<pid>/task/<tid>/maps;
-		# if you don't want the latter, add -maxdepth.
+		# memory mappings are also per process, not per task.
+		# This finds only /proc/<pid>/maps, and not /proc/<pid>/task/<tid>/maps;
+		# if you also want the latter, drop -maxdepth.
 		mmap_procs=$(exec 2>/dev/null;
-			find /proc -path "/proc/[0-9]*/maps" -print |
+			find /proc -mindepth 2 -maxdepth 2 -path "/proc/[0-9]*/maps" -print |
 			xargs -r grep -l " ${dir}/" | awk -F/ '{print $3}' | uniq)
 		printf "${procs}\n${mmap_procs}" | sort -u
 	fi

From 3d34db0c60a125126361b45ff8303358b6275298 Mon Sep 17 00:00:00 2001
From: Lars Ellenberg <lars.ellenberg@linbit.com>
Date: Thu, 16 Oct 2025 11:31:00 +0200
Subject: [PATCH 2/2] Filesystem: futher speed up get_pids

If we have /proc/<pid>/map_files/* symlinks,
we don't need to additionally grep /proc/<pid>/maps.

Also don't first collect output of commands into variables
just to pipe them to sort -u later,
just pipe the output of the commands through sort -u directly.
---
 heartbeat/Filesystem | 31 +++++++++++++++++++------------
 1 file changed, 19 insertions(+), 12 deletions(-)

diff --git a/heartbeat/Filesystem b/heartbeat/Filesystem
index f76339fd6..7021f13da 100755
--- a/heartbeat/Filesystem
+++ b/heartbeat/Filesystem
@@ -694,19 +694,26 @@ get_pids()
 		#
 		# Or trust that fuser (above) learned something in the last 15 years
 		# and avoids blocking operations meanwhile?
-		procs=$(exec 2>/dev/null;
-			find /proc -mindepth 1 -maxdepth 3 \
-				-path "/proc/[0-9]*" \
-				-type l \( -lname "${dir}/*" -o -lname "${dir}" \) -print |
-			awk -F/ '{print $3}' | uniq)
-
-		# memory mappings are also per process, not per task.
-		# This finds only /proc/<pid>/maps, and not /proc/<pid>/task/<tid>/maps;
-		# if you also want the latter, drop -maxdepth.
-		mmap_procs=$(exec 2>/dev/null;
+		(
+		# If you want to debug this, drop this redirection.
+		# But it producess too much "No such file" noise for kernel
+		# threads or due to races with exiting processes or closing fds.
+		exec 2>/dev/null;
+		find /proc -mindepth 1 -maxdepth 3 \
+			-path "/proc/[0-9]*" \
+			-type l \( -lname "${dir}/*" -o -lname "${dir}" \) -print |
+		awk -F/ '{print $3}' | uniq
+
+		# If we have "map_files/", "find" above already found the
+		# relevant symlinks, and we don't need to grep "maps" below.
+		# Available since kernel 3.3, respectively 4.3.
+		test -d /proc/$$/map_files ||
+			# memory mappings are also per process, not per task.
+			# This finds only /proc/<pid>/maps, and not /proc/<pid>/task/<tid>/maps;
+			# if you also want the latter, drop -maxdepth.
 			find /proc -mindepth 2 -maxdepth 2 -path "/proc/[0-9]*/maps" -print |
-			xargs -r grep -l " ${dir}/" | awk -F/ '{print $3}' | uniq)
-		printf "${procs}\n${mmap_procs}" | sort -u
+			xargs -r grep -l " ${dir}/" | awk -F/ '{print $3}' | uniq
+		) | sort -u
 	fi
 }