On 09.06.21 18:28, Claudio Imbrenda wrote:

On Wed, 9 Jun 2021 16:59:17 +0100
Christoph Hellwig [off-list ref] wrote:

quoted

On Tue, Jun 08, 2021 at 08:06:17PM +0200, Claudio Imbrenda wrote:

quoted

The recent patches to add support for hugepage vmalloc mappings
added a flag for __vmalloc_node_range to allow to request small
pages. This flag is not accessible when calling vmalloc, the only
option is to call directly __vmalloc_node_range, which is not
exported.

This means that a module can't vmalloc memory with small pages.

Case in point: KVM on s390x needs to vmalloc a large area, and it
needs to be mapped with small pages, because of a hardware
limitation.

This patch exports __vmalloc_node_range so it can be used in modules
too.

No.  I spent a lot of effort to mak sure such a low-level API is
not exported.

ok, but then how can we vmalloc memory with small pages from KVM?

An alternative would be to provide a vmalloc_no_huge function in generic
code  (similar to  vmalloc_32) (or if preferred in s390 base architecture code)
Something like

void *vmalloc_no_huge(unsigned long size)
{
         return __vmalloc_node_flags(size, NUMA_NO_NODE,VM_NO_HUGE_VMAP |
                                 GFP_KERNEL | __GFP_ZERO);
}
EXPORT_SYMBOL(vmalloc_no_huge);

or a similar vzalloc variant.