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* [PATCH] debugobjects: Allow to configure the amount of pre-allocated objects
@ 2026-02-25 16:05 Benjamin Block
  2026-03-11 10:04 ` Benjamin Block
  2026-03-20 15:26 ` Thomas Gleixner
  0 siblings, 2 replies; 7+ messages in thread
From: Benjamin Block @ 2026-02-25 16:05 UTC (permalink / raw)
  To: Andrew Morton, Thomas Gleixner; +Cc: linux-kernel, linux-s390, Benjamin Block

To debug object operations a certain amount of metadata has to be kept
per object that is tracked. During boot a static amount of pre-
allocated objects is set aside to be used for this task until such a
time a dynamic allocator can be used. Once a dynamic allocator can be
used an initial amount of objects is pre-allocated to be used when
needed.

So far the amount of such initially statically, and later dynamically
pre-allocated objects is set fixed at `64 * 16 = 1024`. But depending on
the system this might not be enough during boot, when only the static
amount of pre-allocated objects is used; and once this happens ODEBUG
disables itself permanently.

On s390 it has been observed, that even with 16384 such pre-allocated
objects ODEBUG would still be disabled during boot.

Similarly to other debug features like KMEMLEAK add a Kconfig option
CONFIG_DEBUG_OBJECTS_POOL_SIZE_SHIFT that allows to increase the amount
of pre-allocated objects (in both the static and later dynamic cases).
Use it as exponential, rather than linear value to allow for head-room
to grow into once set in a configuration.

The calculation is done as such:
    N_OBJECTS = 2^DEBUG_OBJECTS_POOL_SIZE_SHIFT * N_BATCH

By default it is set to 6, so the actual amount is unchanged, unless
the new options is changed:
    N_OBJECTS = 2^6 * 16
    N_OBJECTS = 1024

For the previously mentioned observations on s390 it was necessary to
increase the option to 11 in order to have enough space during boot.

Signed-off-by: Benjamin Block <bblock@linux.ibm.com>
---
 lib/Kconfig.debug  | 32 ++++++++++++++++++++++++++++++++
 lib/debugobjects.c | 15 +++++++++++++--
 2 files changed, 45 insertions(+), 2 deletions(-)

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 318df4c75454..c6afc5b03572 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -811,6 +811,38 @@ config DEBUG_OBJECTS_PERCPU_COUNTER
 	  percpu counter routines to track the life time of percpu counter
 	  objects and validate the percpu counter operations.
 
+config DEBUG_OBJECTS_POOL_SIZE_SHIFT
+	int "Metadata objects pool size"
+	depends on DEBUG_OBJECTS
+	range 0 21
+	default 6
+	help
+	  To debug object operations a certain amount of metadata has to be
+	  kept per object that is tracked. During boot a static amount of pre-
+	  allocated objects is set aside to be used for this task until such a
+	  time a dynamic allocator can be used. Once a dynamic allocator can be
+	  used an initial amount of objects is pre-allocated to be used when
+	  needed.
+
+	  This option sets the amount of both: the amount of initially
+	  statically allocated objects; and later the amount of dynamically
+	  pre-allocated objects. It is used as exponent to the power of 2,
+	  multiplied by the batch size used to set how many objects are move
+	  between pools at once.
+
+	  For example, when left at the default of 6:
+	      N_OBJECTS = 2^DEBUG_OBJECTS_POOL_SIZE_SHIFT * N_BATCH
+	      N_OBJECTS = 2^6 * 16
+	      N_OBJECTS = 1024
+	  By increasing the option by 1, you double the amount of objects.
+
+	  An indication that you need to increase this option is that during
+	  boot you see messages like this:
+	      ODEBUG: Out of memory. ODEBUG disabled
+
+	  If in doubt, leave the default.
+
+
 config DEBUG_OBJECTS_ENABLE_DEFAULT
 	int "debug_objects bootup default value (0-1)"
 	range 0 1
diff --git a/lib/debugobjects.c b/lib/debugobjects.c
index 89a1d6745dc2..20e93d0074fa 100644
--- a/lib/debugobjects.c
+++ b/lib/debugobjects.c
@@ -22,11 +22,18 @@
 #define ODEBUG_HASH_BITS	14
 #define ODEBUG_HASH_SIZE	(1 << ODEBUG_HASH_BITS)
 
-/* Must be power of two */
+/*
+ * Must be power of two.
+ * Please change Kconfig help text of DEBUG_OBJECTS_POOL_SIZE_SHIFT when
+ * changed.
+ */
 #define ODEBUG_BATCH_SIZE	16
 
+#define ODEBUG_POOL_SHIFT	CONFIG_DEBUG_OBJECTS_POOL_SIZE_SHIFT
+static_assert(ODEBUG_POOL_SHIFT >= 0);
+
 /* Initial values. Must all be a multiple of batch size */
-#define ODEBUG_POOL_SIZE	(64 * ODEBUG_BATCH_SIZE)
+#define ODEBUG_POOL_SIZE	((1 << ODEBUG_POOL_SHIFT) * ODEBUG_BATCH_SIZE)
 #define ODEBUG_POOL_MIN_LEVEL	(ODEBUG_POOL_SIZE / 4)
 
 #define ODEBUG_POOL_PERCPU_SIZE	(8 * ODEBUG_BATCH_SIZE)
@@ -569,6 +576,10 @@ static void debug_objects_oom(void)
 	struct debug_bucket *db = obj_hash;
 	HLIST_HEAD(freelist);
 
+	/*
+	 * Please change Kconfig help text of DEBUG_OBJECTS_POOL_SIZE_SHIFT
+	 * when changed.
+	 */
 	pr_warn("Out of memory. ODEBUG disabled\n");
 
 	for (int i = 0; i < ODEBUG_HASH_SIZE; i++, db++) {
-- 
2.53.0


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Thread overview: 7+ messages (download: mbox.gz follow: Atom feed
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2026-02-25 16:05 [PATCH] debugobjects: Allow to configure the amount of pre-allocated objects Benjamin Block
2026-03-11 10:04 ` Benjamin Block
2026-03-11 17:47   ` Andrew Morton
2026-03-13 14:26     ` Benjamin Block
2026-03-14 22:06       ` Andrew Morton
2026-03-17 11:42         ` Benjamin Block
2026-03-20 15:26 ` Thomas Gleixner

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