On Fri, Aug 09, 2019 at 04:05:07PM +0530, Anshuman Khandual wrote: > On 08/09/2019 03:46 PM, Matthew Wilcox wrote: > > On Fri, Aug 09, 2019 at 01:03:17PM +0530, Anshuman Khandual wrote: > >> Should alloc_gigantic_page() be made available as an interface for general > >> use in the kernel. The test module here uses very similar implementation from > >> HugeTLB to allocate a PUD aligned memory block. Similar for mm_alloc() which > >> needs to be exported through a header. > > > > Why are you allocating memory at all instead of just using some > > known-to-exist PFNs like I suggested? > > We needed PFN to be PUD aligned for pfn_pud() and PMD aligned for mk_pmd(). > Now walking the kernel page table for a known symbol like kernel_init() I didn't say to walk the kernel page table. I said to call virt_to_pfn() for a known symbol like kernel_init(). > as you had suggested earlier we might encounter page table page entries at PMD > and PUD which might not be PMD or PUD aligned respectively. It seemed to me > that alignment requirement is applicable only for mk_pmd() and pfn_pud() > which create large mappings at those levels but that requirement does not > exist for page table pages pointing to next level. Is not that correct ? Or > I am missing something here ? Just clear the bottom bits off the PFN until you get a PMD or PUD aligned PFN. It's really not hard.
