On 08/23/2018 05:48 AM, Michal Hocko wrote:
On Tue 21-08-18 18:10:42, Mike Kravetz wrote: [...]
OK, after burning myself when trying to be clever here it seems like your proposed solution is indeed simpler.
+bool huge_pmd_sharing_possible(struct vm_area_struct *vma,
unsigned long *start, unsigned long *end)+{
- unsigned long check_addr = *start;
- bool ret = false;
- if (!(vma->vm_flags & VM_MAYSHARE))
return ret;- for (check_addr = *start; check_addr < *end; check_addr += PUD_SIZE) {
unsigned long a_start = check_addr & PUD_MASK;unsigned long a_end = a_start + PUD_SIZE;I guess this should be rather in HPAGE_SIZE * PTRS_PER_PTE units as huge_pmd_unshare does.
Sure, I can do that.
However, I consider the statement making that calculation in huge_pmd_unshare to be VERY ugly and confusing code.
*addr = ALIGN(*addr, HPAGE_SIZE * PTRS_PER_PTE) - HPAGE_SIZE;
Note that it is adjusting the value of passed argument 'unsigned long *addr'. This argument/value is part of a loop condition in all current callers of huge_pmd_unshare. For instance:
for (; address < end; address += huge_page_size(h)) {
So, that calculation in huge_pmd_unshare gets the calling loop back to the starting address of the unmapped range. It even takes the loop increment 'huge_page_size(h)' into account. That is why that ' - HPAGE_SIZE' is at the end of the calculation.
ugly and confusing! And on my list of things to clean up.