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

Steven Rostedt
2025-02-11T00:03:03Z

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

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