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Message-Id: <20250714143332.264997-1-matt@readmodwrite.com>
Date: Mon, 14 Jul 2025 15:33:32 +0100
From: Matt Fleming <matt@...dmodwrite.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org,
kernel-team@...udflare.com,
Marco Elver <elver@...gle.com>,
Alexander Potapenko <glider@...gle.com>,
Andrey Konovalov <andreyknvl@...il.com>,
Dmitry Vyukov <dvyukov@...gle.com>,
Oscar Salvador <osalvador@...e.de>,
Vlastimil Babka <vbabka@...e.cz>,
Matt Fleming <mfleming@...udflare.com>
Subject: [PATCH] stackdepot: Make max number of pools boot-time configurable
From: Matt Fleming <mfleming@...udflare.com>
We're hitting the WARN in depot_init_pool() about reaching the stack
depot limit because we have long stacks that don't dedup very well.
Introduce a new start-up parameter to allow users to set the number of
maximum stack depot pools.
Signed-off-by: Matt Fleming <mfleming@...udflare.com>
---
.../admin-guide/kernel-parameters.txt | 5 ++
lib/stackdepot.c | 55 +++++++++++++++++--
2 files changed, 56 insertions(+), 4 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index b5cb36148554..6a6d60de4530 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -6542,6 +6542,11 @@
consumed by the stack hash table. By default this is set
to false.
+ stack_depot_max_pools= [KNL,EARLY]
+ Specify the maximum number of pools to use for storing
+ stack traces. Pools are allocated on-demand up to this
+ limit. Default value is 8191 pools.
+
stacktrace [FTRACE]
Enabled the stack tracer on boot up.
diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index 245d5b416699..f66b1d572efb 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -42,6 +42,8 @@
(((1LL << (DEPOT_POOL_INDEX_BITS)) - 1 < DEPOT_POOLS_CAP) ? \
(1LL << (DEPOT_POOL_INDEX_BITS)) - 1 : DEPOT_POOLS_CAP)
+static unsigned int stack_max_pools = DEPOT_MAX_POOLS;
+
static bool stack_depot_disabled;
static bool __stack_depot_early_init_requested __initdata = IS_ENABLED(CONFIG_STACKDEPOT_ALWAYS_INIT);
static bool __stack_depot_early_init_passed __initdata;
@@ -62,7 +64,7 @@ static unsigned int stack_bucket_number_order;
static unsigned int stack_hash_mask;
/* Array of memory regions that store stack records. */
-static void *stack_pools[DEPOT_MAX_POOLS];
+static void **stack_pools;
/* Newly allocated pool that is not yet added to stack_pools. */
static void *new_pool;
/* Number of pools in stack_pools. */
@@ -101,6 +103,33 @@ static int __init disable_stack_depot(char *str)
}
early_param("stack_depot_disable", disable_stack_depot);
+static int __init parse_max_pools(char *str)
+{
+ const long long limit = (1LL << (DEPOT_POOL_INDEX_BITS)) - 1;
+ unsigned int max_pools;
+ int rv;
+
+ rv = kstrtouint(str, 0, &max_pools);
+ if (rv)
+ return rv;
+
+ if (max_pools < 1024) {
+ pr_err("stack_depot_max_pools too low, using default\n");
+ goto out;
+ }
+
+ if (max_pools > limit) {
+ pr_err("stack_depot_max_pools too high, using default\n");
+ goto out;
+
+ }
+
+ stack_max_pools = max_pools;
+out:
+ return 0;
+}
+early_param("stack_depot_max_pools", parse_max_pools);
+
void __init stack_depot_request_early_init(void)
{
/* Too late to request early init now. */
@@ -182,6 +211,15 @@ int __init stack_depot_early_init(void)
}
init_stack_table(entries);
+ pr_info("allocating space for %u stack pools via memblock\n", stack_max_pools);
+ stack_pools = memblock_alloc(stack_max_pools * sizeof(void *), PAGE_SIZE);
+ if (!stack_pools) {
+ pr_err("stack pools allocation failed, disabling\n");
+ memblock_free(stack_table, entries * sizeof(struct list_head));
+ stack_depot_disabled = true;
+ return -ENOMEM;
+ }
+
return 0;
}
@@ -231,6 +269,15 @@ int stack_depot_init(void)
stack_hash_mask = entries - 1;
init_stack_table(entries);
+ pr_info("allocating space for %u stack pools via kvcalloc\n", stack_max_pools);
+ stack_pools = kvcalloc(stack_max_pools, sizeof(void *), GFP_KERNEL);
+ if (!stack_pools) {
+ pr_err("stack pools allocation failed, disabling\n");
+ kvfree(stack_table);
+ stack_depot_disabled = true;
+ ret = -ENOMEM;
+ }
+
out_unlock:
mutex_unlock(&stack_depot_init_mutex);
@@ -245,9 +292,9 @@ static bool depot_init_pool(void **prealloc)
{
lockdep_assert_held(&pool_lock);
- if (unlikely(pools_num >= DEPOT_MAX_POOLS)) {
+ if (unlikely(pools_num >= stack_max_pools)) {
/* Bail out if we reached the pool limit. */
- WARN_ON_ONCE(pools_num > DEPOT_MAX_POOLS); /* should never happen */
+ WARN_ON_ONCE(pools_num > stack_max_pools); /* should never happen */
WARN_ON_ONCE(!new_pool); /* to avoid unnecessary pre-allocation */
WARN_ONCE(1, "Stack depot reached limit capacity");
return false;
@@ -273,7 +320,7 @@ static bool depot_init_pool(void **prealloc)
* NULL; do not reset to NULL if we have reached the maximum number of
* pools.
*/
- if (pools_num < DEPOT_MAX_POOLS)
+ if (pools_num < stack_max_pools)
WRITE_ONCE(new_pool, NULL);
else
WRITE_ONCE(new_pool, STACK_DEPOT_POISON);
--
2.34.1
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