> There are three types of zones:
> 1. The first four zones partition the physical address space of CPU
> memory.
> 2. The device zone provides interoperability between CPU and device
> memory.
> 3. The movable zone commonly represents a memory allocation policy.
>
> +
> +static void __init find_virt_zone(unsigned long occupied, unsigned long *zone_pfn)
> +{
> + int i, nid;
> + unsigned long node_avg, remaining;
Hi Yu,
I discovered that CMA can be part of virtual zones. For example:
Node 0, zone NoMerge
pages free 35945
nr_free_pages 35945
...
nr_free_cma 8128
pagesets
CMA used to be available for order-0 anonymous allocations, and
the Android kernel even prioritized it by commit[1]
"ANDROID: cma: redirect page allocation to CMA"
/*
* Used during anonymous page fault handling.
*/
struct folio *vma_alloc_zeroed_movable_folio(struct vm_area_struct *vma,
unsigned long vaddr)
{
gfp_t flags = GFP_HIGHUSER_MOVABLE | __GFP_ZERO | __GFP_CMA;
/*
* If the page is mapped with PROT_MTE, initialise the tags at the
* point of allocation and page zeroing as this is usually faster than
* separate DC ZVA and STGM.
*/
if (vma->vm_flags & VM_MTE)
flags |= __GFP_ZEROTAGS;
return vma_alloc_folio(flags, 0, vma, vaddr, false);
}
I wonder if cma is still available to order-0 when it is located in
the nomerge/nosplit zone.
And while dma_alloc_coherent() or similar APIs want to get contiguous
memory from cma, are they still as easy as before if cma is a part
of virt zones?
[1] https://android.googlesource.com/kernel/common/+/1c8aebe4c072bf18409cc78fc84407e24a437302
Thanks
Barry
