Re: [PATCH v5 05/10] mm/cma: Introduce cma_alloc_at() API

Re: [PATCH v5 05/10] mm/cma: Introduce cma_alloc_at() API

[Marek Szyprowski]

On 20.08.2026 20:04, David Hildenbrand (Arm) wrote:
>> /* This part must be outside protection */> diff --git a/mm/cma.c b/mm/cma.c
>> index a10ea37a261d..1e1ebae79090 100644
>> --- a/mm/cma.c
>> +++ b/mm/cma.c
>> @@ -936,6 +936,141 @@ struct page *cma_alloc_frozen_compound(struct cma *cma, unsigned int order)
>> return __cma_alloc_frozen(cma, 1 << order, order, gfp);
>> }
>> +static int cma_range_alloc_at(struct cma *cma, struct cma_memrange *cmr,
>> + unsigned long offset, unsigned long count,
>> + struct page **pagep, gfp_t gfp)
>> +{
>> + struct page *page = NULL;
>> + unsigned long pfn;
>> + int ret = -EBUSY;
>> +
>> + spin_lock_irq(&cma->lock);
>> +
>> + /*
>> + * If the request is larger than the available number of pages, stop
>> + * right away.
>> + */
>> + if (count > cma->available_count)
>> + goto unlock;
>> +
>> + ret = bitmap_allocate(cmr->bitmap, offset, count);
>> + if (ret < 0)
>> + goto unlock;
>> +
>> + pfn = cmr->base_pfn + offset;
>> + page = pfn_to_page(pfn);
>> +
>> + /*
>> + * Do not hand out page ranges that are not contiguous, so
>> + * callers can just iterate the pages without having to worry
>> + * about these corner cases.
>> + */
>> + if (!page_range_contiguous(page, count)) {
>> + pr_warn_ratelimited("%s: %s: skipping non-contiguous area [0x%lx-0x%lx]",
>> + __func__, cma->name, pfn, pfn + count - 1);
>> + ret = -EBUSY;
>> + goto clear;
>> + }
>> +
>> + cma->available_count -= count;
>> +
>> + /*
>> + * It's safe to drop the lock here. We've marked this region for
>> + * our exclusive use. If the migration fails we will take the
>> + * lock again and unmark it.
>> + */
>> + spin_unlock_irq(&cma->lock);
>> +
>> + mutex_lock(&cma->alloc_mutex);
>> + ret = alloc_contig_frozen_range(pfn, pfn + count, ACR_FLAGS_CMA, gfp);
>> + mutex_unlock(&cma->alloc_mutex);
>> +
> There is quite some code duplication with cma_range_alloc(). Please try harder
> to factor common code out and reuse it.
>
>
> > ...
> Also here, way too much code duplication with __cma_alloc_frozen().
>
> There must be a better way :)

Maybe the existing 'alloc' functions could call 'alloc_at' variant internally

(with locks adjusted and moved out).


> (I really prefer this direction of the patch set)

Definitely, I also like this approach much more than previous attempt with

'dynamically' instantiated cma regions.



Best regards

-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland