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

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Message-ID: <Z7Q1xY3jhWjaSdeh@kernel.org>
Date: Tue, 18 Feb 2025 09:24:53 +0200
From: Mike Rapoport <rppt@...nel.org>
To: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc: Steven Rostedt <rostedt@...dmis.org>, 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>
Subject: Re: [PATCH v3 1/2] mm/memblock: Add reserved memory release function

Hi Masami,

On Tue, Feb 11, 2025 at 11:47:03PM +0900, Masami Hiramatsu (Google) wrote:
> From: Masami Hiramatsu (Google) <mhiramat@...nel.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@...nel.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Mike Rapoport <rppt@...nel.org>
> Cc: linux-mm@...ck.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@...nel.org>

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

-- 
Sincerely yours,
Mike.