linux-kernel - [PATCH v2] cma: introduce CMA_ALLOC

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Date:   Wed, 9 Aug 2023 18:46:40 +0530
From:   Bibek Kumar Patro <quic_bibekkum@...cinc.com>
To:     <akpm@...ux-foundation.org>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <quic_pkondeti@...cinc.com>, <quic_charante@...cinc.com>,
        Bibek Kumar Patro <quic_bibekkum@...cinc.com>
Subject: [PATCH v2] cma: introduce CMA_ALLOC_DEBUG config

Currently enabling CONFIG_CMA_DEBUG enables DEBUG preprocessor macro.
If DEBUG is defined, it's equivalent to a printk with KERN_DEBUG loglevel
flooding the dmesg buffer with pr_debug prints from mm/cma driver and from
included files as well. This results in excessive amount of CMA logging and
also might distract the debug teams with unrelated KERN_DEBUG prints.One of
the ways engineers currently tackle this problem is by passing loglevel=N
though commandline to suppress KERN_DEBUG messages. This approach can
sometimes become tiresome due to its repetitive nature.
This patch proposes an alternative approach by introducing a simple new
config CONFIG_CMA_ALLOC_DEBUG which only shows the cma bit allocation
status in case of cma failure and do not enable DEBUG preprocessor macro
from CONFIG_CMA_DEBUG avoiding excessive CMA logging from pr_debug.
Engineers and tech teams seeking only for bitmap status in case of cma
failure can use this simple config instead of worrying about changing
the loglevel or trying other similar workarounds.

Signed-off-by: Bibek Kumar Patro <quic_bibekkum@...cinc.com>
---
 mm/Kconfig | 11 +++++++++++
 mm/cma.c   |  2 +-
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/mm/Kconfig b/mm/Kconfig
index 09130434e30d..ad2a20576a65 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -891,12 +891,23 @@ config CMA
 config CMA_DEBUG
 	bool "CMA debug messages (DEVELOPMENT)"
 	depends on DEBUG_KERNEL && CMA
+	select CMA_ALLOC_DEBUG
 	help
 	  Turns on debug messages in CMA.  This produces KERN_DEBUG
 	  messages for every CMA call as well as various messages while
 	  processing calls such as dma_alloc_from_contiguous().
 	  This option does not affect warning and error messages.

+config CMA_ALLOC_DEBUG
+	bool "CMA bitmap status upon failure"
+	depends on CMA
+	help
+	  Turns on bitmap dump in case of cma failures. This prints
+	  current status of CMA bit upon failures and will appear
+	  when cma_alloc() return no_warn argument as false and won't
+	  flood the dmesg buffer with unrelated KERN_DEBUG prints. No
+	  need to explicitly enable this if CMA_DEBUG is enabled.
+
 config CMA_DEBUGFS
 	bool "CMA debugfs interface"
 	depends on CMA && DEBUG_FS
diff --git a/mm/cma.c b/mm/cma.c
index a4cfe995e11e..0ead392769b3 100644
--- a/mm/cma.c
+++ b/mm/cma.c
@@ -383,7 +383,7 @@ int __init cma_declare_contiguous_nid(phys_addr_t base,
 	return ret;
 }

-#ifdef CONFIG_CMA_DEBUG
+#ifdef CONFIG_CMA_ALLOC_DEBUG
 static void cma_debug_show_areas(struct cma *cma)
 {
 	unsigned long next_zero_bit, next_set_bit, nr_zero;
--
2.17.1