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

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

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>