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From:   andrey.konovalov@linux.dev
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     Andrey Konovalov <andreyknvl@gmail.com>,
        Marco Elver <elver@google.com>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Vlastimil Babka <vbabka@suse.cz>, kasan-dev@googlegroups.com,
        Evgenii Stepanov <eugenis@google.com>,
        Oscar Salvador <osalvador@suse.de>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        Andrey Konovalov <andreyknvl@google.com>
Subject: [PATCH v4 22/22] lib/stackdepot: adjust DEPOT_POOLS_CAP for KMSAN
Date:   Mon, 20 Nov 2023 18:47:20 +0100
Message-Id: <301a115cf7ce8ddb42ef6de9151c2bb76ba728fc.1700502145.git.andreyknvl@google.com>
In-Reply-To: <cover.1700502145.git.andreyknvl@google.com>
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From: Andrey Konovalov <andreyknvl@google.com>

KMSAN is frequently used in fuzzing scenarios and thus saves a lot of
stack traces. As KMSAN does not support evicting stack traces from the
stack depot, the stack depot capacity might be reached quickly with large
stack records.

Adjust the maximum number of stack depot pools for this case.

The average size of a stack trace saved into the stack depot is ~16
frames. Thus, adjust the maximum pools number accordingly to keep the
maximum number of stack traces that can be saved into the stack depot
similar to the one that was allowed before the stack trace eviction
changes.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
---
 lib/stackdepot.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/lib/stackdepot.c b/lib/stackdepot.c
index c1b31160f4b4..870cce2f4cbd 100644
--- a/lib/stackdepot.c
+++ b/lib/stackdepot.c
@@ -41,7 +41,17 @@
 #define DEPOT_OFFSET_BITS (DEPOT_POOL_ORDER + PAGE_SHIFT - DEPOT_STACK_ALIGN)
 #define DEPOT_POOL_INDEX_BITS (DEPOT_HANDLE_BITS - DEPOT_OFFSET_BITS - \
 			       STACK_DEPOT_EXTRA_BITS)
+#if IS_ENABLED(CONFIG_KMSAN) && CONFIG_STACKDEPOT_MAX_FRAMES >= 32
+/*
+ * KMSAN is frequently used in fuzzing scenarios and thus saves a lot of stack
+ * traces. As KMSAN does not support evicting stack traces from the stack
+ * depot, the stack depot capacity might be reached quickly with large stack
+ * records. Adjust the maximum number of stack depot pools for this case.
+ */
+#define DEPOT_POOLS_CAP (8192 * (CONFIG_STACKDEPOT_MAX_FRAMES / 16))
+#else
 #define DEPOT_POOLS_CAP 8192
+#endif
 #define DEPOT_MAX_POOLS \
 	(((1LL << (DEPOT_POOL_INDEX_BITS)) < DEPOT_POOLS_CAP) ? \
 	 (1LL << (DEPOT_POOL_INDEX_BITS)) : DEPOT_POOLS_CAP)
-- 
2.25.1