linux-kernel - [PATCH] alloc_tag: introduce Kconfig option for default compressed profiling

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Message-ID: <20250416180653.3438158-1-usamaarif642@gmail.com>
Date: Wed, 16 Apr 2025 19:06:52 +0100
From: Usama Arif <usamaarif642@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
	surenb@...gle.com,
	linux-mm@...ck.org
Cc: hannes@...xchg.org,
	shakeel.butt@...ux.dev,
	linux-kernel@...r.kernel.org,
	kernel-team@...a.com,
	Usama Arif <usamaarif642@...il.com>
Subject: [PATCH] alloc_tag: introduce Kconfig option for default compressed profiling

With this Kconfig option enabled, the kernel stores allocation tag references
in the page flags by default.

There are 2 reasons to introduce this:
- As mentioned in [1], compressed tags dont have system memory overhead
and much lower performance overhead. It would be preferrable to have this as
the default option, and to be able to switch it at compile time. Another
option is to just declare the static key as true by default?
- As compressed option is the best one, it doesn't make sense to have to
change both defconfig and command line options to enable memory
allocation profiling. Changing commandline across a large number of services
can result in signifcant work, which shouldn't be needed if the kernel
defconfig needs to be changed anyways.

[1] https://lore.kernel.org/all/20241023170759.999909-7-surenb@google.com/T/#m0da08879435f7673eaa10871a6e9d1be4f605ac8

Signed-off-by: Usama Arif <usamaarif642@...il.com>
---
 include/linux/pgalloc_tag.h | 4 ++++
 lib/Kconfig.debug           | 5 +++++
 lib/alloc_tag.c             | 4 ++++
 3 files changed, 13 insertions(+)

diff --git a/include/linux/pgalloc_tag.h b/include/linux/pgalloc_tag.h
index c74077977830..0226059bcf00 100644
--- a/include/linux/pgalloc_tag.h
+++ b/include/linux/pgalloc_tag.h
@@ -16,7 +16,11 @@ extern unsigned long alloc_tag_ref_mask;
 extern int alloc_tag_ref_offs;
 extern struct alloc_tag_kernel_section kernel_tags;
 
+#ifdef CONFIG_MEM_ALLOC_PROFILING_COMPRESSED_ENABLED_BY_DEFAULT
+DECLARE_STATIC_KEY_TRUE(mem_profiling_compressed);
+#else
 DECLARE_STATIC_KEY_FALSE(mem_profiling_compressed);
+#endif
 
 typedef u16	pgalloc_tag_idx;
 
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 9fe4d8dfe578..66d8995f3514 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1028,6 +1028,11 @@ config MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT
 	default y
 	depends on MEM_ALLOC_PROFILING
 
+config MEM_ALLOC_PROFILING_COMPRESSED_ENABLED_BY_DEFAULT
+	bool "store page allocation tag references in the page flags by default"
+	default y
+	depends on MEM_ALLOC_PROFILING
+
 config MEM_ALLOC_PROFILING_DEBUG
 	bool "Memory allocation profiler debugging"
 	default n
diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c
index 25ecc1334b67..30adad5630dd 100644
--- a/lib/alloc_tag.c
+++ b/lib/alloc_tag.c
@@ -31,7 +31,11 @@ DEFINE_STATIC_KEY_MAYBE(CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT,
 			mem_alloc_profiling_key);
 EXPORT_SYMBOL(mem_alloc_profiling_key);
 
+#ifdef CONFIG_MEM_ALLOC_PROFILING_COMPRESSED_ENABLED_BY_DEFAULT
+DEFINE_STATIC_KEY_TRUE(mem_profiling_compressed);
+#else
 DEFINE_STATIC_KEY_FALSE(mem_profiling_compressed);
+#endif
 
 struct alloc_tag_kernel_section kernel_tags = { NULL, 0 };
 unsigned long alloc_tag_ref_mask;
-- 
2.47.1