Re: [PATCH v2 1/2] mm/vmalloc: export __vmalloc_node_range

[Christian Borntraeger]

On 09.06.21 18:49, Uladzislau Rezki wrote:
> On Wed, Jun 09, 2021 at 06:28:09PM +0200, Claudio Imbrenda wrote:
> > On Wed, 9 Jun 2021 16:59:17 +0100
> > Christoph Hellwig <hch@xxxxxxxxxxxxx> wrote:
> >
> > > On Tue, Jun 08, 2021 at 08:06:17PM +0200, Claudio Imbrenda wrote:
> > > > 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?
> Does the s390x support CONFIG_HAVE_ARCH_HUGE_VMALLOC what is arch
> specific?

Not yet, but we surely want that for almost everything on s390.
Only this particular firmware interface does not handle large pages
for donated memory.

> If not then small pages are used. Or am i missing something?
>
> I agree with Christoph that exporting a low level internals
> is not a good idea.