linux-kernel - [PATCH 1/3] kmemleak: drop (age <increasing>) from leak record

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Date:   Tue, 25 Apr 2023 16:24:44 -0600
From:   Jim Cromie <jim.cromie@...il.com>
To:     catalin.marinas@....com, linux-mm@...ck.org
Cc:     linux-kernel@...r.kernel.org, Jim Cromie <jim.cromie@...il.com>
Subject: [PATCH 1/3] kmemleak: drop (age <increasing>) from leak record

Displaying age is pretty, but counter-productive; it surrenders
idempotency of the output, which breaks simple hash-based cataloging
of the records by the user.

The trouble: sequential reads, wo new leaks, get new results:

  :#> sum /sys/kernel/debug/kmemleak
  53439    74 /sys/kernel/debug/kmemleak
  :#> sum /sys/kernel/debug/kmemleak
  59066    74 /sys/kernel/debug/kmemleak

and age is why (nothing else changes):

  :#> grep -v age /sys/kernel/debug/kmemleak | sum
  58894    67
  :#> grep -v age /sys/kernel/debug/kmemleak | sum
  58894    67

Further, age is not an intrinsic property of the leak, its an artifact
of when it was scanned, and relative age is embedded in leak order.

While userspace could work around the always-changing output, ISTM
none could be relying upon age in any important way, and having
idempotent output is just better.

Signed-off-by: Jim Cromie <jim.cromie@...il.com>
---
 mm/kmemleak.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/mm/kmemleak.c b/mm/kmemleak.c
index a2d34226e3c8..f025c7bc845b 100644
--- a/mm/kmemleak.c
+++ b/mm/kmemleak.c
@@ -355,14 +355,12 @@ static void print_unreferenced(struct seq_file *seq,
 	int i;
 	unsigned long *entries;
 	unsigned int nr_entries;
-	unsigned int msecs_age = jiffies_to_msecs(jiffies - object->jiffies);
 
 	nr_entries = stack_depot_fetch(object->trace_handle, &entries);
 	warn_or_seq_printf(seq, "unreferenced object 0x%08lx (size %zu):\n",
 			  object->pointer, object->size);
-	warn_or_seq_printf(seq, "  comm \"%s\", pid %d, jiffies %lu (age %d.%03ds)\n",
-			   object->comm, object->pid, object->jiffies,
-			   msecs_age / 1000, msecs_age % 1000);
+	warn_or_seq_printf(seq, "  comm \"%s\", pid %d, jiffies %lu\n",
+			   object->comm, object->pid, object->jiffies);
 	hex_dump_object(seq, object);
 	warn_or_seq_printf(seq, "  backtrace:\n");
 
-- 
2.40.0