linux-kernel - Re: [RFC PATCH v2 2/3] mm/memblock: Add reserved memory release function

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Message-ID: <20250210190306.6ffda2c7@gandalf.local.home>
Date: Mon, 10 Feb 2025 19:03:06 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org, Mark
 Rutland <mark.rutland@....com>, Mathieu Desnoyers
 <mathieu.desnoyers@...icios.com>, Andrew Morton
 <akpm@...ux-foundation.org>, Mike Rapoport <rppt@...nel.org>
Subject: Re: [RFC PATCH v2 2/3] mm/memblock: Add reserved memory release
 function

On Tue, 11 Feb 2025 00:44:08 +0900
"Masami Hiramatsu (Google)" <mhiramat@...nel.org> wrote:

> From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> 
> Add reserved_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.

Since Mike wrote the reserve_mem code, we should Cc him on changes.

Also, I would make patches 2 and 3 a separate patchset, as it is unrelated
to the other code.

> 
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@...nel.org>
> ---
>  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..a7201824c1fc 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 reserved_mem_release_by_name(const char *name);

Should be "reserve_mem_release_by_name()" and not "reserved_mem" to stay consistent.

>  
>  #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..9962fbb90597 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(reserved_mem_lock);

"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)(&reserved_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);
>  
> +/**
> + * reserved_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 reserved_mem_release_by_name(const char *name)
> +{
> +	struct reserve_mem_table *map;
> +	unsigned int page_count;
> +	phys_addr_t start;
> +
> +	guard(mutex)(&reserved_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
>   */


Thanks,

-- Steve