Re: [PATCH v2 02/17] memblock: Declare scratch memory as CMA

[Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>]

On Fri, Dec 22, 2023 at 07:35:52PM +0000, Alexander Graf wrote:
> When we finish populating our memory, we don't want to lose the scratch
> region as memory we can use for useful data. Do do that, we mark it as
> CMA memory. That means that any allocation within it only happens with
> movable memory which we can then happily discard for the next kexec.
> 
> That way we don't lose the scratch region's memory anymore for
> allocations after boot.
> 
> Signed-off-by: Alexander Graf <graf@amazon.com>
> 
> ---
> 
> v1 -> v2:
> 
>   - test bot warning fix
> ---
>  mm/memblock.c | 30 ++++++++++++++++++++++++++----
>  1 file changed, 26 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/memblock.c b/mm/memblock.c
> index e89e6c8f9d75..3700c2c1a96d 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/page-isolation.h>
>  
>  #include <asm/sections.h>
>  #include <linux/io.h>
> @@ -1100,10 +1101,6 @@ static bool should_skip_region(struct memblock_type *type,
>  	if ((flags & MEMBLOCK_SCRATCH) && !memblock_is_scratch(m))
>  		return true;
>  
> -	/* Leave scratch memory alone after scratch-only phase */
> -	if (!(flags & MEMBLOCK_SCRATCH) && memblock_is_scratch(m))
> -		return true;
> -
>  	return false;
>  }
>  
> @@ -2153,6 +2150,20 @@ static void __init __free_pages_memory(unsigned long start, unsigned long end)
>  	}
>  }
>  
> +#ifdef CONFIG_MEMBLOCK_SCRATCH
> +static void reserve_scratch_mem(phys_addr_t start, phys_addr_t end)

nit: the function name doesn't look reasonable as it has nothing
limiting it to neither reservation nor scratch mem.
Perhaps something like "set_mem_cma_type" would be a better fit.

> +{
> +	ulong start_pfn = pageblock_start_pfn(PFN_DOWN(start));
> +	ulong end_pfn = pageblock_align(PFN_UP(end));
> +	ulong pfn;
> +
> +	for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages) {
> +		/* Mark as CMA to prevent kernel allocations in it */

nit: the comment above looks irrelevant/redundant.

> +		set_pageblock_migratetype(pfn_to_page(pfn), MIGRATE_CMA);
> +	}
> +}
> +#endif
> +
>  static unsigned long __init __free_memory_core(phys_addr_t start,
>  				 phys_addr_t end)
>  {
> @@ -2214,6 +2225,17 @@ static unsigned long __init free_low_memory_core_early(void)
>  
>  	memmap_init_reserved_pages();
>  
> +#ifdef CONFIG_MEMBLOCK_SCRATCH
> +	/*
> +	 * Mark scratch mem as CMA before we return it. That way we ensure that
> +	 * no kernel allocations happen on it. That means we can reuse it as
> +	 * scratch memory again later.
> +	 */
> +	__for_each_mem_range(i, &memblock.memory, NULL, NUMA_NO_NODE,
> +			     MEMBLOCK_SCRATCH, &start, &end, NULL)
> +		reserve_scratch_mem(start, end);
> +#endif
> +
>  	/*
>  	 * We need to use NUMA_NO_NODE instead of NODE_DATA(0)->node_id
>  	 *  because in some case like Node0 doesn't have RAM installed
> -- 
> 2.40.1
> 
> 
> 
> 
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