Re: [PATCH v3 02/17] memblock: Declare scratch memory as CMA

From: Pratyush Yadav <ptyadav@amazon.de>
To: Alexander Graf <graf@amazon.com>
Cc: <linux-kernel@vger.kernel.org>,
	<linux-trace-kernel@vger.kernel.org>, <linux-mm@kvack.org>,
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	"H . Peter Anvin" <hpa@zytor.com>,
	Andy Lutomirski <luto@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Steven Rostedt <rostedt@goodmis.org>,
	Andrew Morton <akpm@linux-foundation.org>,
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	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	Rob Herring <robh+dt@kernel.org>,
	"Krzysztof Kozlowski" <krzk@kernel.org>
Subject: Re: [PATCH v3 02/17] memblock: Declare scratch memory as CMA
Date: Fri, 23 Feb 2024 16:53:25 +0100	[thread overview]
Message-ID: <mafs0r0h36utm.fsf@amazon.de> (raw)
In-Reply-To: <20240117144704.602-3-graf@amazon.com> (Alexander Graf's message of "Wed, 17 Jan 2024 14:46:49 +0000")

Hi,

On Wed, Jan 17 2024, 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>
>
[...]
> @@ -2188,6 +2185,16 @@ static void __init __free_pages_memory(unsigned long start, unsigned long end)
>  	}
>  }
>  
> +static void mark_phys_as_cma(phys_addr_t start, phys_addr_t end)
> +{
> +	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)
> +		set_pageblock_migratetype(pfn_to_page(pfn), MIGRATE_CMA);

This fails to compile if CONFIG_CMA is disabled. I think you should add
it as a dependency for CONFIG_MEMBLOCK_SCRATCH.

> +}
> +
>  static unsigned long __init __free_memory_core(phys_addr_t start,
>  				 phys_addr_t end)
>  {
> @@ -2249,6 +2256,17 @@ static unsigned long __init free_low_memory_core_early(void)
>  
>  	memmap_init_reserved_pages();
>  
> +	if (IS_ENABLED(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)
> +			mark_phys_as_cma(start, end);
> +	}
> +
>  	/*
>  	 * 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

-- 
Regards,
Pratyush Yadav

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