On Tue, 2018-05-29 at 16:44 +0200, Joerg Roedel wrote:
On Wed, May 16, 2018 at 05:32:07PM -0600, Toshi Kani wrote:
pmd = (pmd_t *)pud_page_vaddr(*pud);
- pmd_sv = (pmd_t *)__get_free_page(GFP_KERNEL);
- if (!pmd_sv)
return 0;So your code still needs to allocate a full page where a simple list_head on the stack would do the same job.
Can you explain why you think allocating a page here is a major problem?
As I explained before, pud_free_pmd_page() covers an extremely rare case which I could not even hit with a huge number of ioremap() calls until I instrumented alloc_vmap_area() to force this case to happen. I do not think pages should be listed for such a rare case.
Ingo, Thomas, can you please just revert the original broken patch for now until there is proper fix?
If we just revert, please apply patch 1/3 first. This patch address the BUG_ON issue on PAE. This is a real issue that needs a fix ASAP.
The page-directory cache issue on x64, which is addressed by patch 3/3, is a theoretical issue that I could not hit by putting ioremap() calls into a loop for a whole day. Nobody hit this issue, either.
The simple revert patch Joerg posted a while ago causes pmd_free_pte_page() to fail on x64. This causes multiple pmd mappings to fall into pte mappings on my test systems. This can be seen as a degradation, and I am afraid that it is more harmful than good.
Thanks, -Toshi