On Sat, Mar 21, 2020 at 09:43:17AM +0100, Christoph Hellwig wrote:

On Fri, Mar 20, 2020 at 01:49:04PM -0300, Jason Gunthorpe wrote:

...

From: Jason Gunthorpe jgg@mellanox.com

This code can be compiled when CONFIG_TRANSPARENT_HUGEPAGE is off, so remove the ifdef.

It can compile, but will the compiler optimize it away?

Yes, the enclosing conditional:

if (pmd_devmap(pmd) || pmd_trans_huge(pmd)) {

is statically false if !CONFIG_TRANSPARENT_HUGEPAGE

This is proven today, as the fallback stub is a function prototype with no implementation:

-int hmm_vma_handle_pmd(struct mm_walk *walk, unsigned long addr, - unsigned long end, uint64_t *pfns, pmd_t pmd);

If the compiler wasn't optimizing the above branch we'd get link failures.

Jason