linux-kernel - Re: [PATCH 3/3] dma-pool: limit DMA and DMA32 zone size pools

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Date:   Wed, 17 Aug 2022 13:50:09 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Christoph Hellwig <hch@....de>, iommu@...ts.linux.dev,
        Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     Michal Hocko <mhocko@...e.com>,
        David Rientjes <rientjes@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] dma-pool: limit DMA and DMA32 zone size pools

On 2022-08-17 07:06, Christoph Hellwig wrote:
> Limit the sizing of the atomic pools for allocations from
> ZONE_DMA and ZONE_DMA32 based on the number of pages actually
> present in those zones instead of the total memory.
> 
> Fixes: c84dc6e68a1d ("dma-pool: add additional coherent pools to map to gfp mask")
> Reported-by: Michal Hocko <mhocko@...e.com>
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>   kernel/dma/pool.c | 40 +++++++++++++++++++++++++++++-----------
>   1 file changed, 29 insertions(+), 11 deletions(-)
> 
> diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
> index 5b07b0379a501..f629c6dfd8555 100644
> --- a/kernel/dma/pool.c
> +++ b/kernel/dma/pool.c
> @@ -193,28 +193,46 @@ static unsigned long calculate_pool_size(unsigned long zone_pages)
>   	return max_t(unsigned long, nr_pages << PAGE_SHIFT, SZ_128K);
>   }
>   
> +#if defined(CONFIG_ZONE_DMA) || defined(CONFIG_ZONE_DMA32)

This #ifdeffery seems horribly clunky - I think it would be much nicer 
to mark this __maybe_unused, and preserve the has_managed_dma/IS_ENABLED 
logic below.

> +static unsigned long __init nr_managed_pages(int zone_idx)
> +{
> +	struct pglist_data *pgdat;
> +	unsigned long nr_pages = 0;
> +
> +	for_each_online_pgdat(pgdat)
> +		nr_pages += zone_managed_pages(&pgdat->node_zones[zone_idx]);
> +	return nr_pages;
> +}
> +#endif /* CONFIG_ZONE_DMA || CONFIG_ZONE_DMA32 */
> +
>   static int __init dma_atomic_pool_init(void)
>   {
> +	unsigned long nr_zone_dma_pages, nr_zone_dma32_pages;

...otherwise, I expect the buildbots will be along shortly with unused 
variable warnings for these :)

Cheers,
Robin.

> +
> +#ifdef CONFIG_ZONE_DMA
> +	nr_zone_dma_pages = nr_managed_pages(ZONE_DMA);
> +	if (nr_zone_dma_pages)
> +		atomic_pool_dma = __dma_atomic_pool_init(
> +				calculate_pool_size(nr_zone_dma_pages),
> +				GFP_DMA);
> +#endif
> +#ifdef CONFIG_ZONE_DMA32
> +	nr_zone_dma32_pages = nr_managed_pages(ZONE_DMA32);
> +	if (nr_zone_dma32_pages)
> +		atomic_pool_dma32 = __dma_atomic_pool_init(
> +				calculate_pool_size(nr_zone_dma32_pages),
> +				GFP_DMA32);
> +#endif
>   	/*
>   	 * If coherent_pool was not used on the command line, default the pool
>   	 * sizes to 128KB per 1GB of memory, min 128KB, max MAX_ORDER-1.
>   	 */
>   	if (!atomic_pool_size)
>   		atomic_pool_size = calculate_pool_size(totalram_pages());
> -
> -	INIT_WORK(&atomic_pool_work, atomic_pool_work_fn);
> -
>   	atomic_pool_kernel = __dma_atomic_pool_init(atomic_pool_size,
>   						    GFP_KERNEL);
> -	if (has_managed_dma()) {
> -		atomic_pool_dma = __dma_atomic_pool_init(atomic_pool_size,
> -						GFP_KERNEL | GFP_DMA);
> -	}
> -	if (IS_ENABLED(CONFIG_ZONE_DMA32)) {
> -		atomic_pool_dma32 = __dma_atomic_pool_init(atomic_pool_size,
> -						GFP_KERNEL | GFP_DMA32);
> -	}
>   
> +	INIT_WORK(&atomic_pool_work, atomic_pool_work_fn);
>   	dma_atomic_pool_debugfs_init();
>   	return 0;
>   }