Re: [RFC PATCH 2/4] dma/pool: Add an API to check if DMA allocation is from pool

[Samiullah Khawaja <skhawaja@google.com>]

On Mon, Jun 08, 2026 at 06:10:02PM +0000, Pranjal Shrivastava wrote:
>On Tue, May 05, 2026 at 12:27:35AM +0000, Samiullah Khawaja wrote:
>> DMA allocations can be done through DMA pools, add an API that can be
>> used to check if an allocation is done from a pool. This will be used in
>> the later commit during preservation of DMA allocation.
>>
>> Signed-off-by: Samiullah Khawaja <skhawaja@google.com>
>> ---
>>  include/linux/dma-map-ops.h |  1 +
>>  kernel/dma/pool.c           | 13 +++++++++++++
>>  2 files changed, 14 insertions(+)
>>
>> diff --git a/include/linux/dma-map-ops.h b/include/linux/dma-map-ops.h
>> index 6a1832a73cad..6a0bc4ea2467 100644
>> --- a/include/linux/dma-map-ops.h
>> +++ b/include/linux/dma-map-ops.h
>> @@ -216,6 +216,7 @@ struct page *dma_alloc_from_pool(struct device *dev, size_t size,
>>  		bool (*phys_addr_ok)(struct device *, phys_addr_t, size_t));
>>  bool dma_free_from_pool(struct device *dev, void *start, size_t size);
>>
>> +bool dma_is_from_pool(struct device *dev, void *start, size_t size);
>>  int dma_direct_set_offset(struct device *dev, phys_addr_t cpu_start,
>>  		dma_addr_t dma_start, u64 size);
>>
>> diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
>> index 2b2fbb709242..32ce4d6d7683 100644
>> --- a/kernel/dma/pool.c
>> +++ b/kernel/dma/pool.c
>> @@ -307,3 +307,16 @@ bool dma_free_from_pool(struct device *dev, void *start, size_t size)
>>
>>  	return false;
>>  }
>> +
>> +bool dma_is_from_pool(struct device *dev, void *start, size_t size)
>
>Do we need struct device here? It seems unused?
>
>Nit: we only ever pass 0 gfp_flags to dma_guess_pool, should we instead
>name it: dma_is_from_atomic_pool() to be more accurate?

dma_guess_pool() goes through all of them when passing 0, look at the
prev logic inside it and how it is used by the dma_free_from_pool(). But
you are right they are all atomic, but semantically we want to check
whether it is part of any pool so lets keep it as is. WDYT?
>
>> +{
>> +	struct gen_pool *pool = NULL;
>> +
>> +	while ((pool = dma_guess_pool(pool, 0))) {
>> +		if (!gen_pool_has_addr(pool, (unsigned long)start, size))
>> +			continue;
>> +		return true;
>> +	}
>
>Nit: The loop looks slightly ugly, can we have:
>
>struct gen_pool *pool;
>
>for (pool = dma_guess_pool(NULL, 0); pool != NULL; pool = dma_guess_pool(pool, 0)) {
>	if (gen_pool_has_addr(pool, (unsigned long)start, size))
>		return true;
>}

It is a basically a copy dma_free_from_pool() without the free part, so
keeping the style consistent.
>
>> +
>> +	return false;
>> +}
>> --
>> 2.54.0.545.g6539524ca2-goog
>>
>
>Thanks,
>Praan

Thanks,
Sami