[PATCH 0/3] slab: switch away from the legacy param parser

[PATCH 0/3] slab: switch away from the legacy param parser

[Petr Tesarik]

The handling of legacy __setup() parameters has some confusing quirks.
Instead of fixing them, convert the code to struct kerenel_param, which
is a saner API.

Note that parameters defined with core_param() and __core_param_cb() are
parsed early in start_kernel(). Do not confuse them with core_param_cb(),
which are processed at a later stage.

Petr Tesarik (3):
  slab: constify slab debug strings
  slab: convert setup_slub_debug() to use __core_param_cb()
  slab: use core_param for remaining command line parameters

 mm/slub.c | 87 ++++++++++++++++++++++++++++++++-----------------------
 1 file changed, 51 insertions(+), 36 deletions(-)

-- 
2.51.0

[PATCH 1/3] slab: constify slab debug strings

[Petr Tesarik]

Since the string passed to slab_debug is never modified, use pointers to
const char in all places where it is processed.

No functional changes intended.

Signed-off-by: Petr Tesarik <ptesarik@suse.com>
---
 mm/slub.c | 19 ++++++++++---------
 1 file changed, 10 insertions(+), 9 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 708848d3512c5..26faebcf27a2b 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -978,7 +978,7 @@ static slab_flags_t slub_debug = DEBUG_DEFAULT_FLAGS;
 static slab_flags_t slub_debug;
 #endif
 
-static char *slub_debug_string;
+static const char *slub_debug_string __ro_after_init;
 static int disable_higher_order_debug;
 
 /*
@@ -1785,8 +1785,8 @@ static inline int free_consistency_checks(struct kmem_cache *s,
  *
  * returns the start of next block if there's any, or NULL
  */
-static char *
-parse_slub_debug_flags(char *str, slab_flags_t *flags, char **slabs, bool init)
+static const char *
+parse_slub_debug_flags(const char *str, slab_flags_t *flags, const char **slabs, bool init)
 {
 	bool higher_order_disable = false;
 
@@ -1863,14 +1863,15 @@ parse_slub_debug_flags(char *str, slab_flags_t *flags, char **slabs, bool init)
 		return NULL;
 }
 
-static int __init setup_slub_debug(char *str)
+static int __init setup_slub_debug(char *val)
 {
 	slab_flags_t flags;
 	slab_flags_t global_flags;
-	char *saved_str;
-	char *slab_list;
+	const char *saved_str;
+	const char *slab_list;
 	bool global_slub_debug_changed = false;
 	bool slab_list_specified = false;
+	const char *str = val;
 
 	global_flags = DEBUG_DEFAULT_FLAGS;
 	if (*str++ != '=' || !*str)
@@ -1935,9 +1936,9 @@ __setup_param("slub_debug", slub_debug, setup_slub_debug, 0);
  */
 slab_flags_t kmem_cache_flags(slab_flags_t flags, const char *name)
 {
-	char *iter;
+	const char *iter;
 	size_t len;
-	char *next_block;
+	const char *next_block;
 	slab_flags_t block_flags;
 	slab_flags_t slub_debug_local = slub_debug;
 
@@ -1961,7 +1962,7 @@ slab_flags_t kmem_cache_flags(slab_flags_t flags, const char *name)
 			continue;
 		/* Found a block that has a slab list, search it */
 		while (*iter) {
-			char *end, *glob;
+			const char *end, *glob;
 			size_t cmplen;
 
 			end = strchrnul(iter, ',');
-- 
2.51.0

Re: [PATCH 1/3] slab: constify slab debug strings

[Christoph Lameter (Ampere)]

Reviewed-by: Christoph Lameter <cl@gentwo.org>

Re: [PATCH 1/3] slab: constify slab debug strings

[Harry Yoo]

On Fri, Oct 24, 2025 at 07:06:52PM +0200, Petr Tesarik wrote:
> Since the string passed to slab_debug is never modified, use pointers to
> const char in all places where it is processed.
> 
> No functional changes intended.
> 
> Signed-off-by: Petr Tesarik <ptesarik@suse.com>
> ---

Looks good to me,
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>

-- 
Cheers,
Harry / Hyeonggon

[PATCH 2/3] slab: convert setup_slub_debug() to use __core_param_cb()

[Petr Tesarik]

Use __core_param_cb() to parse the "slab_debug" kernel parameter instead of
the obsolescent __setup(). For now, the parameter is not exposed in sysfs,
and no get ops is provided.

There is a slight change in behavior. Before this patch, the following
parameter would silently turn on full debugging for all slabs:

  slub_debug_yada_yada_gotta_love_this=hail_satan!

This syntax is now rejected, and the parameter will be passed to user
space, making the kernel a holier place.

Signed-off-by: Petr Tesarik <ptesarik@suse.com>
---
 mm/slub.c | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 26faebcf27a2b..b124087b95f32 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1863,7 +1863,7 @@ parse_slub_debug_flags(const char *str, slab_flags_t *flags, const char **slabs,
 		return NULL;
 }
 
-static int __init setup_slub_debug(char *val)
+static int __init setup_slub_debug(const char *str, const struct kernel_param *kp)
 {
 	slab_flags_t flags;
 	slab_flags_t global_flags;
@@ -1871,10 +1871,9 @@ static int __init setup_slub_debug(char *val)
 	const char *slab_list;
 	bool global_slub_debug_changed = false;
 	bool slab_list_specified = false;
-	const char *str = val;
 
 	global_flags = DEBUG_DEFAULT_FLAGS;
-	if (*str++ != '=' || !*str)
+	if (!str || !*str)
 		/*
 		 * No options specified. Switch on full debugging.
 		 */
@@ -1918,11 +1917,15 @@ static int __init setup_slub_debug(char *val)
 	     static_branch_unlikely(&init_on_free)) &&
 	    (slub_debug & SLAB_POISON))
 		pr_info("mem auto-init: SLAB_POISON will take precedence over init_on_alloc/init_on_free\n");
-	return 1;
+	return 0;
 }
 
-__setup("slab_debug", setup_slub_debug);
-__setup_param("slub_debug", slub_debug, setup_slub_debug, 0);
+static const struct kernel_param_ops param_ops_slab_debug __initconst = {
+	.flags = KERNEL_PARAM_OPS_FL_NOARG,
+	.set = setup_slub_debug,
+};
+__core_param_cb(slab_debug, &param_ops_slab_debug, NULL, 0);
+__core_param_cb(slub_debug, &param_ops_slab_debug, NULL, 0);
 
 /*
  * kmem_cache_flags - apply debugging options to the cache
-- 
2.51.0

Re: [PATCH 2/3] slab: convert setup_slub_debug() to use __core_param_cb()

[Harry Yoo]

On Fri, Oct 24, 2025 at 07:06:53PM +0200, Petr Tesarik wrote:
> Use __core_param_cb() to parse the "slab_debug" kernel parameter instead of
> the obsolescent __setup(). For now, the parameter is not exposed in sysfs,
> and no get ops is provided.
> 
> There is a slight change in behavior. Before this patch, the following
> parameter would silently turn on full debugging for all slabs:
> 
>   slub_debug_yada_yada_gotta_love_this=hail_satan!
> 
> This syntax is now rejected, and the parameter will be passed to user
> space, making the kernel a holier place.
> 
> Signed-off-by: Petr Tesarik <ptesarik@suse.com>
> ---

Good byte to slub_debug_yada_yada_gotta_love_this=hail_satan! :'(

Looks good to me,
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>

-- 
Cheers,
Harry / Hyeonggon

[PATCH 3/3] slab: use new API for remaining command line parameters

[Petr Tesarik]

Use core_param() and __core_param_cb() instead of __setup() or
__setup_param() to improve syntax checking and error messages.

Replace get_option() with kstrtouint(), because:
* the latter accepts a pointer to const char,
* these parameters should not accept ranges,
* error value can be passed directly to parser.

There is one more change apart from the parsing of numeric parameters:
slub_strict_numa parameter name must match exactly. Before this patch the
kernel would silently accept any option that starts with the name as an
undocumented alias.

Signed-off-by: Petr Tesarik <ptesarik@suse.com>
---
 mm/slub.c | 57 +++++++++++++++++++++++++++++++++----------------------
 1 file changed, 34 insertions(+), 23 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index b124087b95f32..482460ff3abca 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -8119,46 +8119,53 @@ void __kmem_obj_info(struct kmem_obj_info *kpp, void *object, struct slab *slab)
  *		Kmalloc subsystem
  *******************************************************************/
 
-static int __init setup_slub_min_order(char *str)
+static int __init setup_slub_min_order(const char *str, const struct kernel_param *kp)
 {
-	get_option(&str, (int *)&slub_min_order);
+	int ret;
+
+	ret = kstrtouint(str, 0, &slub_min_order);
+	if (ret)
+		return ret;
 
 	if (slub_min_order > slub_max_order)
 		slub_max_order = slub_min_order;
 
-	return 1;
+	return 0;
 }
 
-__setup("slab_min_order=", setup_slub_min_order);
-__setup_param("slub_min_order=", slub_min_order, setup_slub_min_order, 0);
-
+static const struct kernel_param_ops param_ops_slab_min_order __initconst = {
+	.set = setup_slub_min_order,
+};
+__core_param_cb(slab_min_order, &param_ops_slab_min_order, &slub_min_order, 0);
+__core_param_cb(slub_min_order, &param_ops_slab_min_order, &slub_min_order, 0);
 
-static int __init setup_slub_max_order(char *str)
+static int __init setup_slub_max_order(const char *str, const struct kernel_param *kp)
 {
-	get_option(&str, (int *)&slub_max_order);
+	int ret;
+
+	ret = kstrtouint(str, 0, &slub_max_order);
+	if (ret)
+		return ret;
+
 	slub_max_order = min_t(unsigned int, slub_max_order, MAX_PAGE_ORDER);
 
 	if (slub_min_order > slub_max_order)
 		slub_min_order = slub_max_order;
 
-	return 1;
+	return 0;
 }
 
-__setup("slab_max_order=", setup_slub_max_order);
-__setup_param("slub_max_order=", slub_max_order, setup_slub_max_order, 0);
-
-static int __init setup_slub_min_objects(char *str)
-{
-	get_option(&str, (int *)&slub_min_objects);
-
-	return 1;
-}
+static const struct kernel_param_ops param_ops_slab_max_order __initconst = {
+	.set = setup_slub_max_order,
+};
+__core_param_cb(slab_max_order, &param_ops_slab_max_order, &slub_max_order, 0);
+__core_param_cb(slub_max_order, &param_ops_slab_max_order, &slub_max_order, 0);
 
-__setup("slab_min_objects=", setup_slub_min_objects);
-__setup_param("slub_min_objects=", slub_min_objects, setup_slub_min_objects, 0);
+core_param(slab_min_objects, slub_min_objects, uint, 0);
+core_param(slub_min_objects, slub_min_objects, uint, 0);
 
 #ifdef CONFIG_NUMA
-static int __init setup_slab_strict_numa(char *str)
+static int __init setup_slab_strict_numa(const char *str, const struct kernel_param *kp)
 {
 	if (nr_node_ids > 1) {
 		static_branch_enable(&strict_numa);
@@ -8167,10 +8174,14 @@ static int __init setup_slab_strict_numa(char *str)
 		pr_warn("slab_strict_numa parameter set on non NUMA system.\n");
 	}
 
-	return 1;
+	return 0;
 }
 
-__setup("slab_strict_numa", setup_slab_strict_numa);
+static const struct kernel_param_ops param_ops_slab_strict_numa __initconst = {
+	.flags = KERNEL_PARAM_OPS_FL_NOARG,
+	.set = setup_slab_strict_numa,
+};
+__core_param_cb(slab_strict_numa, &param_ops_slab_strict_numa, NULL, 0);
 #endif
 
 
-- 
2.51.0

Re: [PATCH 3/3] slab: use new API for remaining command line parameters

[Harry Yoo]

On Fri, Oct 24, 2025 at 07:06:54PM +0200, Petr Tesarik wrote:
> Use core_param() and __core_param_cb() instead of __setup() or
> __setup_param() to improve syntax checking and error messages.
> 
> Replace get_option() with kstrtouint(), because:
> * the latter accepts a pointer to const char,
> * these parameters should not accept ranges,
> * error value can be passed directly to parser.
> 
> There is one more change apart from the parsing of numeric parameters:
> slub_strict_numa parameter name must match exactly. Before this patch the

nit: ^ slab_strict_numa

> kernel would silently accept any option that starts with the name as an
> undocumented alias.
> 
> Signed-off-by: Petr Tesarik <ptesarik@suse.com>
> ---

Looks good to me,
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>

-- 
Cheers,
Harry / Hyeonggon

Re: [PATCH 3/3] slab: use new API for remaining command line parameters

[Petr Tesarik]

On Wed, 29 Oct 2025 19:52:46 +0900
Harry Yoo <harry.yoo@oracle.com> wrote:

> On Fri, Oct 24, 2025 at 07:06:54PM +0200, Petr Tesarik wrote:
> > Use core_param() and __core_param_cb() instead of __setup() or
> > __setup_param() to improve syntax checking and error messages.
> > 
> > Replace get_option() with kstrtouint(), because:
> > * the latter accepts a pointer to const char,
> > * these parameters should not accept ranges,
> > * error value can be passed directly to parser.
> > 
> > There is one more change apart from the parsing of numeric parameters:
> > slub_strict_numa parameter name must match exactly. Before this patch the  
> 
> nit: ^ slab_strict_numa

Indeed.

Petr T

Re: [PATCH 3/3] slab: use new API for remaining command line parameters

[Vlastimil Babka]

On 10/30/25 14:32, Petr Tesarik wrote:
> On Wed, 29 Oct 2025 19:52:46 +0900
> Harry Yoo <harry.yoo@oracle.com> wrote:
> 
>> On Fri, Oct 24, 2025 at 07:06:54PM +0200, Petr Tesarik wrote:
>> > Use core_param() and __core_param_cb() instead of __setup() or
>> > __setup_param() to improve syntax checking and error messages.
>> > 
>> > Replace get_option() with kstrtouint(), because:
>> > * the latter accepts a pointer to const char,
>> > * these parameters should not accept ranges,
>> > * error value can be passed directly to parser.
>> > 
>> > There is one more change apart from the parsing of numeric parameters:
>> > slub_strict_numa parameter name must match exactly. Before this patch the  
>> 
>> nit: ^ slab_strict_numa

Ah right, thanks, fixed up.

> Indeed.
> 
> Petr T

Re: [PATCH 0/3] slab: switch away from the legacy param parser

[Vlastimil Babka]

On 10/24/25 19:06, Petr Tesarik wrote:
> The handling of legacy __setup() parameters has some confusing quirks.
> Instead of fixing them, convert the code to struct kerenel_param, which
> is a saner API.
> 
> Note that parameters defined with core_param() and __core_param_cb() are
> parsed early in start_kernel(). Do not confuse them with core_param_cb(),
> which are processed at a later stage.

Thanks! Added to slab/for-next

> Petr Tesarik (3):
>   slab: constify slab debug strings
>   slab: convert setup_slub_debug() to use __core_param_cb()
>   slab: use core_param for remaining command line parameters
> 
>  mm/slub.c | 87 ++++++++++++++++++++++++++++++++-----------------------
>  1 file changed, 51 insertions(+), 36 deletions(-)
> 

Re: [PATCH 0/3] slab: switch away from the legacy param parser

[Petr Tesarik]

On Mon, 27 Oct 2025 16:06:21 +0100
Vlastimil Babka <vbabka@suse.cz> wrote:

> On 10/24/25 19:06, Petr Tesarik wrote:
> > The handling of legacy __setup() parameters has some confusing quirks.
> > Instead of fixing them, convert the code to struct kerenel_param, which
> > is a saner API.
> > 
> > Note that parameters defined with core_param() and __core_param_cb() are
> > parsed early in start_kernel(). Do not confuse them with core_param_cb(),
> > which are processed at a later stage.  
> 
> Thanks! Added to slab/for-next

Thank you! Appreciated.

Petr T