[PATCH v3 0/2] tracing: Make persistent ring buffer freeable

[PATCH v3 0/2] tracing: Make persistent ring buffer freeable

[Masami Hiramatsu (Google)]

Hi,

Here is a pair of patches for making the persistent ring buffer
freeable. These were splitted from another series for improving
persistent ring buffer [1].

[1] https://lore.kernel.org/all/173920222697.826592.3726270716809214055.stgit@devnote2/

Anyway, this series allows us to release the memory for the persistent
ring buffer if it is not used anymore without changing kernel cmdline
and reboot. This allows us to enable the persistent ring buffer by
default boot, but disable it according to the user setting after boot
and recycle the memory for the persistent ring buffer.

This is important for the secure system which signs kernel cmdline with
the kernel image, because user can not change the cmdline easily
(usually, it is not possible unless changing kernel image.) Thus, to
use the persistent ring buffer, we need to enable it by default on such
system. However, in that case, some amount of memory is locked by the
persistent ring buffer even if it is not used by user setting.

This feature is useful for such case, because if user setting is
disabled the persistent tracing, we can release the persistent ring
buffer to free page pool.

Thank you,
---

Masami Hiramatsu (Google) (2):
      mm/memblock: Add reserved memory release function
      tracing: Freeable reserved ring buffer


 include/linux/mm.h   |    1 +
 kernel/trace/trace.c |   13 ++++++++-
 kernel/trace/trace.h |    1 +
 mm/memblock.c        |   72 ++++++++++++++++++++++++++++++++++++++++++--------
 4 files changed, 74 insertions(+), 13 deletions(-)

--
Masami Hiramatsu (Google) <mhiramat@kernel.org>

[PATCH v3 1/2] mm/memblock: Add reserved memory release function

[Masami Hiramatsu (Google)]

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Add reserve_mem_release_by_name() to release a reserved memory region
with a given name. This allows us to release reserved memory which is
defined by kernel cmdline, after boot.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: linux-mm@kvack.org
---
 Changes in v2:
  - Rename reserved_mem_* to reserve_mem_*.
---
 include/linux/mm.h |    1 +
 mm/memblock.c      |   72 +++++++++++++++++++++++++++++++++++++++++++---------
 2 files changed, 61 insertions(+), 12 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index f02925447e59..fe5f7711df04 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -4197,6 +4197,7 @@ void vma_pgtable_walk_begin(struct vm_area_struct *vma);
 void vma_pgtable_walk_end(struct vm_area_struct *vma);
 
 int reserve_mem_find_by_name(const char *name, phys_addr_t *start, phys_addr_t *size);
+int reserve_mem_release_by_name(const char *name);
 
 #ifdef CONFIG_64BIT
 int do_mseal(unsigned long start, size_t len_in, unsigned long flags);
diff --git a/mm/memblock.c b/mm/memblock.c
index 095c18b5c430..c8d207ebb93c 100644
--- a/mm/memblock.c
+++ b/mm/memblock.c
@@ -16,6 +16,7 @@
 #include <linux/kmemleak.h>
 #include <linux/seq_file.h>
 #include <linux/memblock.h>
+#include <linux/mutex.h>
 
 #include <asm/sections.h>
 #include <linux/io.h>
@@ -2263,6 +2264,7 @@ struct reserve_mem_table {
 };
 static struct reserve_mem_table reserved_mem_table[RESERVE_MEM_MAX_ENTRIES];
 static int reserved_mem_count;
+static DEFINE_MUTEX(reserve_mem_lock);
 
 /* Add wildcard region with a lookup name */
 static void __init reserved_mem_add(phys_addr_t start, phys_addr_t size,
@@ -2276,6 +2278,21 @@ static void __init reserved_mem_add(phys_addr_t start, phys_addr_t size,
 	strscpy(map->name, name);
 }
 
+static struct reserve_mem_table *reserve_mem_find_by_name_nolock(const char *name)
+{
+	struct reserve_mem_table *map;
+	int i;
+
+	for (i = 0; i < reserved_mem_count; i++) {
+		map = &reserved_mem_table[i];
+		if (!map->size)
+			continue;
+		if (strcmp(name, map->name) == 0)
+			return map;
+	}
+	return NULL;
+}
+
 /**
  * reserve_mem_find_by_name - Find reserved memory region with a given name
  * @name: The name that is attached to a reserved memory region
@@ -2289,22 +2306,53 @@ static void __init reserved_mem_add(phys_addr_t start, phys_addr_t size,
 int reserve_mem_find_by_name(const char *name, phys_addr_t *start, phys_addr_t *size)
 {
 	struct reserve_mem_table *map;
-	int i;
 
-	for (i = 0; i < reserved_mem_count; i++) {
-		map = &reserved_mem_table[i];
-		if (!map->size)
-			continue;
-		if (strcmp(name, map->name) == 0) {
-			*start = map->start;
-			*size = map->size;
-			return 1;
-		}
-	}
-	return 0;
+	guard(mutex)(&reserve_mem_lock);
+	map = reserve_mem_find_by_name_nolock(name);
+	if (!map)
+		return 0;
+
+	*start = map->start;
+	*size = map->size;
+	return 1;
 }
 EXPORT_SYMBOL_GPL(reserve_mem_find_by_name);
 
+/**
+ * reserve_mem_release_by_name - Release reserved memory region with a given name
+ * @name: The name that is attatched to a reserved memory region
+ *
+ * Forcibly release the pages in the reserved memory region so that those memory
+ * can be used as free memory. After released the reserved region size becomes 0.
+ *
+ * Returns: 1 if released or 0 if not found.
+ */
+int reserve_mem_release_by_name(const char *name)
+{
+	struct reserve_mem_table *map;
+	unsigned int page_count;
+	phys_addr_t start;
+
+	guard(mutex)(&reserve_mem_lock);
+	map = reserve_mem_find_by_name_nolock(name);
+	if (!map)
+		return 0;
+
+	start = map->start;
+	page_count = DIV_ROUND_UP(map->size, PAGE_SIZE);
+
+	for (int i = 0; i < page_count; i++) {
+		phys_addr_t addr = start + i * PAGE_SIZE;
+		struct page *page = pfn_to_page(addr >> PAGE_SHIFT);
+
+		page->flags &= ~BIT(PG_reserved);
+		__free_page(page);
+	}
+	map->size = 0;
+
+	return 1;
+}
+
 /*
  * Parse reserve_mem=nn:align:name
  */

Re: [PATCH v3 1/2] mm/memblock: Add reserved memory release function

[Steven Rostedt]

On Tue, 11 Feb 2025 23:47:03 +0900
"Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:

> From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> 
> Add reserve_mem_release_by_name() to release a reserved memory region
> with a given name. This allows us to release reserved memory which is
> defined by kernel cmdline, after boot.
> 
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Mike Rapoport <rppt@kernel.org>
> Cc: linux-mm@kvack.org

Hi, can we get one of the Memory Management maintainers to ack this patch?

We will be having devices going out with the reserve_mem option to perform
tracing in the field. But that only happens if the user grants permission
to do so. But the kernel command line does not change between users that
granted permission and those that do not. We would like to free up the
memory for those devices where the users did not grant permission to trace,
as then the memory is just wasted.

Thanks!

-- Steve


> ---
>  Changes in v2:
>   - Rename reserved_mem_* to reserve_mem_*.
> ---
>  include/linux/mm.h |    1 +
>  mm/memblock.c      |   72 +++++++++++++++++++++++++++++++++++++++++++---------
>  2 files changed, 61 insertions(+), 12 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index f02925447e59..fe5f7711df04 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -4197,6 +4197,7 @@ void vma_pgtable_walk_begin(struct vm_area_struct *vma);
>  void vma_pgtable_walk_end(struct vm_area_struct *vma);
>  
>  int reserve_mem_find_by_name(const char *name, phys_addr_t *start, phys_addr_t *size);
> +int reserve_mem_release_by_name(const char *name);
>  
>  #ifdef CONFIG_64BIT
>  int do_mseal(unsigned long start, size_t len_in, unsigned long flags);
> diff --git a/mm/memblock.c b/mm/memblock.c
> index 095c18b5c430..c8d207ebb93c 100644
> --- a/mm/memblock.c
> +++ b/mm/memblock.c
> @@ -16,6 +16,7 @@
>  #include <linux/kmemleak.h>
>  #include <linux/seq_file.h>
>  #include <linux/memblock.h>
> +#include <linux/mutex.h>
>  
>  #include <asm/sections.h>
>  #include <linux/io.h>
> @@ -2263,6 +2264,7 @@ struct reserve_mem_table {
>  };
>  static struct reserve_mem_table reserved_mem_table[RESERVE_MEM_MAX_ENTRIES];
>  static int reserved_mem_count;
> +static DEFINE_MUTEX(reserve_mem_lock);
>  
>  /* Add wildcard region with a lookup name */
>  static void __init reserved_mem_add(phys_addr_t start, phys_addr_t size,
> @@ -2276,6 +2278,21 @@ static void __init reserved_mem_add(phys_addr_t start, phys_addr_t size,
>  	strscpy(map->name, name);
>  }
>  
> +static struct reserve_mem_table *reserve_mem_find_by_name_nolock(const char *name)
> +{
> +	struct reserve_mem_table *map;
> +	int i;
> +
> +	for (i = 0; i < reserved_mem_count; i++) {
> +		map = &reserved_mem_table[i];
> +		if (!map->size)
> +			continue;
> +		if (strcmp(name, map->name) == 0)
> +			return map;
> +	}
> +	return NULL;
> +}
> +
>  /**
>   * reserve_mem_find_by_name - Find reserved memory region with a given name
>   * @name: The name that is attached to a reserved memory region
> @@ -2289,22 +2306,53 @@ static void __init reserved_mem_add(phys_addr_t start, phys_addr_t size,
>  int reserve_mem_find_by_name(const char *name, phys_addr_t *start, phys_addr_t *size)
>  {
>  	struct reserve_mem_table *map;
> -	int i;
>  
> -	for (i = 0; i < reserved_mem_count; i++) {
> -		map = &reserved_mem_table[i];
> -		if (!map->size)
> -			continue;
> -		if (strcmp(name, map->name) == 0) {
> -			*start = map->start;
> -			*size = map->size;
> -			return 1;
> -		}
> -	}
> -	return 0;
> +	guard(mutex)(&reserve_mem_lock);
> +	map = reserve_mem_find_by_name_nolock(name);
> +	if (!map)
> +		return 0;
> +
> +	*start = map->start;
> +	*size = map->size;
> +	return 1;
>  }
>  EXPORT_SYMBOL_GPL(reserve_mem_find_by_name);
>  
> +/**
> + * reserve_mem_release_by_name - Release reserved memory region with a given name
> + * @name: The name that is attatched to a reserved memory region
> + *
> + * Forcibly release the pages in the reserved memory region so that those memory
> + * can be used as free memory. After released the reserved region size becomes 0.
> + *
> + * Returns: 1 if released or 0 if not found.
> + */
> +int reserve_mem_release_by_name(const char *name)
> +{
> +	struct reserve_mem_table *map;
> +	unsigned int page_count;
> +	phys_addr_t start;
> +
> +	guard(mutex)(&reserve_mem_lock);
> +	map = reserve_mem_find_by_name_nolock(name);
> +	if (!map)
> +		return 0;
> +
> +	start = map->start;
> +	page_count = DIV_ROUND_UP(map->size, PAGE_SIZE);
> +
> +	for (int i = 0; i < page_count; i++) {
> +		phys_addr_t addr = start + i * PAGE_SIZE;
> +		struct page *page = pfn_to_page(addr >> PAGE_SHIFT);
> +
> +		page->flags &= ~BIT(PG_reserved);
> +		__free_page(page);
> +	}
> +	map->size = 0;
> +
> +	return 1;
> +}
> +
>  /*
>   * Parse reserve_mem=nn:align:name
>   */

Re: [PATCH v3 1/2] mm/memblock: Add reserved memory release function

[Masami Hiramatsu]

On Tue, 11 Feb 2025 12:52:11 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Tue, 11 Feb 2025 23:47:03 +0900
> "Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:
> 
> > From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> > 
> > Add reserve_mem_release_by_name() to release a reserved memory region
> > with a given name. This allows us to release reserved memory which is
> > defined by kernel cmdline, after boot.
> > 
> > Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: Mike Rapoport <rppt@kernel.org>
> > Cc: linux-mm@kvack.org
> 
> Hi, can we get one of the Memory Management maintainers to ack this patch?
> 
> We will be having devices going out with the reserve_mem option to perform
> tracing in the field. But that only happens if the user grants permission
> to do so. But the kernel command line does not change between users that
> granted permission and those that do not. We would like to free up the
> memory for those devices where the users did not grant permission to trace,
> as then the memory is just wasted.

Thanks Steve for explaining, I missed Ccing the background information.
Here is the covermail of this series.

https://lore.kernel.org/all/173928521419.906035.17750338150436695675.stgit@devnote2/

Thank you,

> 
> Thanks!
> 
> -- Steve
> 
> 
> > ---
> >  Changes in v2:
> >   - Rename reserved_mem_* to reserve_mem_*.
> > ---
> >  include/linux/mm.h |    1 +
> >  mm/memblock.c      |   72 +++++++++++++++++++++++++++++++++++++++++++---------
> >  2 files changed, 61 insertions(+), 12 deletions(-)
> > 
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index f02925447e59..fe5f7711df04 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -4197,6 +4197,7 @@ void vma_pgtable_walk_begin(struct vm_area_struct *vma);
> >  void vma_pgtable_walk_end(struct vm_area_struct *vma);
> >  
> >  int reserve_mem_find_by_name(const char *name, phys_addr_t *start, phys_addr_t *size);
> > +int reserve_mem_release_by_name(const char *name);
> >  
> >  #ifdef CONFIG_64BIT
> >  int do_mseal(unsigned long start, size_t len_in, unsigned long flags);
> > diff --git a/mm/memblock.c b/mm/memblock.c
> > index 095c18b5c430..c8d207ebb93c 100644
> > --- a/mm/memblock.c
> > +++ b/mm/memblock.c
> > @@ -16,6 +16,7 @@
> >  #include <linux/kmemleak.h>
> >  #include <linux/seq_file.h>
> >  #include <linux/memblock.h>
> > +#include <linux/mutex.h>
> >  
> >  #include <asm/sections.h>
> >  #include <linux/io.h>
> > @@ -2263,6 +2264,7 @@ struct reserve_mem_table {
> >  };
> >  static struct reserve_mem_table reserved_mem_table[RESERVE_MEM_MAX_ENTRIES];
> >  static int reserved_mem_count;
> > +static DEFINE_MUTEX(reserve_mem_lock);
> >  
> >  /* Add wildcard region with a lookup name */
> >  static void __init reserved_mem_add(phys_addr_t start, phys_addr_t size,
> > @@ -2276,6 +2278,21 @@ static void __init reserved_mem_add(phys_addr_t start, phys_addr_t size,
> >  	strscpy(map->name, name);
> >  }
> >  
> > +static struct reserve_mem_table *reserve_mem_find_by_name_nolock(const char *name)
> > +{
> > +	struct reserve_mem_table *map;
> > +	int i;
> > +
> > +	for (i = 0; i < reserved_mem_count; i++) {
> > +		map = &reserved_mem_table[i];
> > +		if (!map->size)
> > +			continue;
> > +		if (strcmp(name, map->name) == 0)
> > +			return map;
> > +	}
> > +	return NULL;
> > +}
> > +
> >  /**
> >   * reserve_mem_find_by_name - Find reserved memory region with a given name
> >   * @name: The name that is attached to a reserved memory region
> > @@ -2289,22 +2306,53 @@ static void __init reserved_mem_add(phys_addr_t start, phys_addr_t size,
> >  int reserve_mem_find_by_name(const char *name, phys_addr_t *start, phys_addr_t *size)
> >  {
> >  	struct reserve_mem_table *map;
> > -	int i;
> >  
> > -	for (i = 0; i < reserved_mem_count; i++) {
> > -		map = &reserved_mem_table[i];
> > -		if (!map->size)
> > -			continue;
> > -		if (strcmp(name, map->name) == 0) {
> > -			*start = map->start;
> > -			*size = map->size;
> > -			return 1;
> > -		}
> > -	}
> > -	return 0;
> > +	guard(mutex)(&reserve_mem_lock);
> > +	map = reserve_mem_find_by_name_nolock(name);
> > +	if (!map)
> > +		return 0;
> > +
> > +	*start = map->start;
> > +	*size = map->size;
> > +	return 1;
> >  }
> >  EXPORT_SYMBOL_GPL(reserve_mem_find_by_name);
> >  
> > +/**
> > + * reserve_mem_release_by_name - Release reserved memory region with a given name
> > + * @name: The name that is attatched to a reserved memory region
> > + *
> > + * Forcibly release the pages in the reserved memory region so that those memory
> > + * can be used as free memory. After released the reserved region size becomes 0.
> > + *
> > + * Returns: 1 if released or 0 if not found.
> > + */
> > +int reserve_mem_release_by_name(const char *name)
> > +{
> > +	struct reserve_mem_table *map;
> > +	unsigned int page_count;
> > +	phys_addr_t start;
> > +
> > +	guard(mutex)(&reserve_mem_lock);
> > +	map = reserve_mem_find_by_name_nolock(name);
> > +	if (!map)
> > +		return 0;
> > +
> > +	start = map->start;
> > +	page_count = DIV_ROUND_UP(map->size, PAGE_SIZE);
> > +
> > +	for (int i = 0; i < page_count; i++) {
> > +		phys_addr_t addr = start + i * PAGE_SIZE;
> > +		struct page *page = pfn_to_page(addr >> PAGE_SHIFT);
> > +
> > +		page->flags &= ~BIT(PG_reserved);
> > +		__free_page(page);
> > +	}
> > +	map->size = 0;
> > +
> > +	return 1;
> > +}
> > +
> >  /*
> >   * Parse reserve_mem=nn:align:name
> >   */
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>

Re: [PATCH v3 1/2] mm/memblock: Add reserved memory release function

[Mike Rapoport]

Hi Masami,

On Tue, Feb 11, 2025 at 11:47:03PM +0900, Masami Hiramatsu (Google) wrote:
> From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> 
> Add reserve_mem_release_by_name() to release a reserved memory region
> with a given name. This allows us to release reserved memory which is
> defined by kernel cmdline, after boot.
> 
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Mike Rapoport <rppt@kernel.org>
> Cc: linux-mm@kvack.org

...

> +/**
> + * reserve_mem_release_by_name - Release reserved memory region with a given name
> + * @name: The name that is attatched to a reserved memory region
> + *
> + * Forcibly release the pages in the reserved memory region so that those memory
> + * can be used as free memory. After released the reserved region size becomes 0.
> + *
> + * Returns: 1 if released or 0 if not found.
> + */
> +int reserve_mem_release_by_name(const char *name)
> +{
> +	struct reserve_mem_table *map;
> +	unsigned int page_count;
> +	phys_addr_t start;
> +
> +	guard(mutex)(&reserve_mem_lock);
> +	map = reserve_mem_find_by_name_nolock(name);
> +	if (!map)
> +		return 0;
> +
> +	start = map->start;
> +	page_count = DIV_ROUND_UP(map->size, PAGE_SIZE);
> +
> +	for (int i = 0; i < page_count; i++) {
> +		phys_addr_t addr = start + i * PAGE_SIZE;
> +		struct page *page = pfn_to_page(addr >> PAGE_SHIFT);
> +
> +		page->flags &= ~BIT(PG_reserved);
> +		__free_page(page);
> +	}

We have free_reserved_area(), please use it here.
Otherwise

Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

> +	map->size = 0;
> +
> +	return 1;
> +}
> +
>  /*
>   * Parse reserve_mem=nn:align:name
>   */
> 

-- 
Sincerely yours,
Mike.

Re: [PATCH v3 1/2] mm/memblock: Add reserved memory release function

[Masami Hiramatsu]

Hi Mike,

On Tue, 18 Feb 2025 09:24:53 +0200
Mike Rapoport <rppt@kernel.org> wrote:

> Hi Masami,
> 
> On Tue, Feb 11, 2025 at 11:47:03PM +0900, Masami Hiramatsu (Google) wrote:
> > From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> > 
> > Add reserve_mem_release_by_name() to release a reserved memory region
> > with a given name. This allows us to release reserved memory which is
> > defined by kernel cmdline, after boot.
> > 
> > Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: Mike Rapoport <rppt@kernel.org>
> > Cc: linux-mm@kvack.org
> 
> ...
> 
> > +/**
> > + * reserve_mem_release_by_name - Release reserved memory region with a given name
> > + * @name: The name that is attatched to a reserved memory region
> > + *
> > + * Forcibly release the pages in the reserved memory region so that those memory
> > + * can be used as free memory. After released the reserved region size becomes 0.
> > + *
> > + * Returns: 1 if released or 0 if not found.
> > + */
> > +int reserve_mem_release_by_name(const char *name)
> > +{
> > +	struct reserve_mem_table *map;
> > +	unsigned int page_count;
> > +	phys_addr_t start;
> > +
> > +	guard(mutex)(&reserve_mem_lock);
> > +	map = reserve_mem_find_by_name_nolock(name);
> > +	if (!map)
> > +		return 0;
> > +
> > +	start = map->start;
> > +	page_count = DIV_ROUND_UP(map->size, PAGE_SIZE);
> > +
> > +	for (int i = 0; i < page_count; i++) {
> > +		phys_addr_t addr = start + i * PAGE_SIZE;
> > +		struct page *page = pfn_to_page(addr >> PAGE_SHIFT);
> > +
> > +		page->flags &= ~BIT(PG_reserved);
> > +		__free_page(page);
> > +	}
> 
> We have free_reserved_area(), please use it here.
> Otherwise
> 
> Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

Thanks! but I can not use free_reserved_area() here because it uses
virt_to_page(). Here we only know the physical address in the map.
I think we can use free_reserved_page() instead. Is that OK?

Thank you,


> 
> > +	map->size = 0;
> > +
> > +	return 1;
> > +}
> > +
> >  /*
> >   * Parse reserve_mem=nn:align:name
> >   */
> > 
> 
> -- 
> Sincerely yours,
> Mike.


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>

Re: [PATCH v3 1/2] mm/memblock: Add reserved memory release function

[Mike Rapoport]

On Tue, Feb 18, 2025 at 05:42:57PM +0900, Masami Hiramatsu wrote:
> Hi Mike,
> 
> On Tue, 18 Feb 2025 09:24:53 +0200
> Mike Rapoport <rppt@kernel.org> wrote:
> 
> > Hi Masami,
> > 
> > On Tue, Feb 11, 2025 at 11:47:03PM +0900, Masami Hiramatsu (Google) wrote:
> > > From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> > > 
> > > Add reserve_mem_release_by_name() to release a reserved memory region
> > > with a given name. This allows us to release reserved memory which is
> > > defined by kernel cmdline, after boot.
> > > 
> > > Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> > > Cc: Andrew Morton <akpm@linux-foundation.org>
> > > Cc: Mike Rapoport <rppt@kernel.org>
> > > Cc: linux-mm@kvack.org
> > 
> > ...
> > 
> > > +/**
> > > + * reserve_mem_release_by_name - Release reserved memory region with a given name
> > > + * @name: The name that is attatched to a reserved memory region
> > > + *
> > > + * Forcibly release the pages in the reserved memory region so that those memory
> > > + * can be used as free memory. After released the reserved region size becomes 0.
> > > + *
> > > + * Returns: 1 if released or 0 if not found.
> > > + */
> > > +int reserve_mem_release_by_name(const char *name)
> > > +{
> > > +	struct reserve_mem_table *map;
> > > +	unsigned int page_count;
> > > +	phys_addr_t start;
> > > +
> > > +	guard(mutex)(&reserve_mem_lock);
> > > +	map = reserve_mem_find_by_name_nolock(name);
> > > +	if (!map)
> > > +		return 0;
> > > +
> > > +	start = map->start;
> > > +	page_count = DIV_ROUND_UP(map->size, PAGE_SIZE);
> > > +
> > > +	for (int i = 0; i < page_count; i++) {
> > > +		phys_addr_t addr = start + i * PAGE_SIZE;
> > > +		struct page *page = pfn_to_page(addr >> PAGE_SHIFT);
> > > +
> > > +		page->flags &= ~BIT(PG_reserved);
> > > +		__free_page(page);
> > > +	}
> > 
> > We have free_reserved_area(), please use it here.
> > Otherwise
> > 
> > Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> 
> Thanks! but I can not use free_reserved_area() here because it uses
> virt_to_page(). Here we only know the physical address in the map.
> I think we can use free_reserved_page() instead. Is that OK?

For reserve_mem ranges virt_to_phys() will work, they are allocated from the
memory that is covered by the direct map.
 
> Thank you,
> 
> -- 
> Masami Hiramatsu (Google) <mhiramat@kernel.org>

-- 
Sincerely yours,
Mike.

Re: [PATCH v3 1/2] mm/memblock: Add reserved memory release function

[Mike Rapoport]

On Tue, Feb 18, 2025 at 11:47:11AM +0200, Mike Rapoport wrote:
> On Tue, Feb 18, 2025 at 05:42:57PM +0900, Masami Hiramatsu wrote:
> > Hi Mike,
> > 
> > 
> > Thanks! but I can not use free_reserved_area() here because it uses
> > virt_to_page(). Here we only know the physical address in the map.
> > I think we can use free_reserved_page() instead. Is that OK?
> 
> For reserve_mem ranges virt_to_phys() will work, they are allocated from the

I meant phys_to_virt() of course :)

> memory that is covered by the direct map.

-- 
Sincerely yours,
Mike.

Re: [PATCH v3 1/2] mm/memblock: Add reserved memory release function

[Masami Hiramatsu]

On Tue, 18 Feb 2025 13:34:51 +0200
Mike Rapoport <rppt@kernel.org> wrote:

> On Tue, Feb 18, 2025 at 11:47:11AM +0200, Mike Rapoport wrote:
> > On Tue, Feb 18, 2025 at 05:42:57PM +0900, Masami Hiramatsu wrote:
> > > Hi Mike,
> > > 
> > > 
> > > Thanks! but I can not use free_reserved_area() here because it uses
> > > virt_to_page(). Here we only know the physical address in the map.
> > > I think we can use free_reserved_page() instead. Is that OK?
> > 
> > For reserve_mem ranges virt_to_phys() will work, they are allocated from the
> 
> I meant phys_to_virt() of course :)

Ah, I got it :). Let me update it.

Thanks!

> 
> > memory that is covered by the direct map.
> 
> -- 
> Sincerely yours,
> Mike.


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>

[PATCH v3 2/2] tracing: Freeable reserved ring buffer

[Masami Hiramatsu (Google)]

From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Make the ring buffer on reserved memory to be freeable. This allows us
to free the trace instance on the reserved memory without changing
cmdline and rebooting. Even if we can not change the kernel cmdline
for security reason, we can release the reserved memory for the ring
buffer as free (available) memory.

For example, boot kernel with reserved memory;
"reserve_mem=20M:2M:trace trace_instance=boot_mapped^traceoff@trace"

 # free
              total        used        free      shared  buff/cache   available
Mem:        1994720       45292     1931960       14908       17468     1915920
Swap:             0           0           0
 # rmdir /sys/kernel/tracing/instances/boot_mapped/
 # free
              total        used        free      shared  buff/cache   available
Mem:        1994720       17204     1960060       14912       17456     1944012
Swap:             0           0           0

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
 Changes in v3:
  - Remove debug printk.
---
 kernel/trace/trace.c |   13 ++++++++++++-
 kernel/trace/trace.h |    1 +
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 1496a5ac33ae..9c7921ec7e91 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -9286,6 +9286,9 @@ static void free_trace_buffers(struct trace_array *tr)
 #ifdef CONFIG_TRACER_MAX_TRACE
 	free_trace_buffer(&tr->max_buffer);
 #endif
+
+	if (tr->range_addr_start)
+		vunmap((void *)tr->range_addr_start);
 }
 
 static void init_trace_flags_index(struct trace_array *tr)
@@ -9447,6 +9450,7 @@ trace_array_create_systems(const char *name, const char *systems,
 	free_cpumask_var(tr->pipe_cpumask);
 	free_cpumask_var(tr->tracing_cpumask);
 	kfree_const(tr->system_names);
+	kfree(tr->range_name);
 	kfree(tr->name);
 	kfree(tr);
 
@@ -9573,6 +9577,11 @@ static int __remove_instance(struct trace_array *tr)
 	free_trace_buffers(tr);
 	clear_tracing_err_log(tr);
 
+	if (tr->range_name) {
+		reserve_mem_release_by_name(tr->range_name);
+		kfree(tr->range_name);
+	}
+
 	for (i = 0; i < tr->nr_topts; i++) {
 		kfree(tr->topts[i].topts);
 	}
@@ -10370,6 +10379,7 @@ __init static void enable_instances(void)
 		bool traceoff = false;
 		char *flag_delim;
 		char *addr_delim;
+		char *rname __free(kfree) = NULL;
 
 		tok = strsep(&curr_str, ",");
 
@@ -10426,6 +10436,7 @@ __init static void enable_instances(void)
 				pr_warn("Failed to map boot instance %s to %s\n", name, tok);
 				continue;
 			}
+			rname = kstrdup(tok, GFP_KERNEL);
 		}
 
 		if (start) {
@@ -10462,7 +10473,7 @@ __init static void enable_instances(void)
 		 */
 		if (start) {
 			tr->flags |= TRACE_ARRAY_FL_BOOT;
-			tr->ref++;
+			tr->range_name = no_free_ptr(rname);
 		}
 
 		while ((tok = strsep(&curr_str, ","))) {
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 9c21ba45b7af..93b6279d3da4 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -348,6 +348,7 @@ struct trace_array {
 	unsigned int		mapped;
 	unsigned long		range_addr_start;
 	unsigned long		range_addr_size;
+	char			*range_name;
 	long			text_delta;
 	long			data_delta;