Re: [PATCH v3 1/2] mm: migration: fix migration of huge PMD shared pages

On 08/23/2018 10:01 AM, Mike Kravetz wrote:

On 08/23/2018 05:48 AM, Michal Hocko wrote:

quoted

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.

quoted

+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.

On second thought, this is more similar to vma_shareable() which uses
PUD_MASK and PUD_SIZE.  In fact Kirill asked me to put in a common helper
for this and vma_shareable.  So, I would prefer to leave it as PUD* unless
you feel strongly.

IMO, it would make more sense to change this in huge_pmd_unshare as PMD
sharing is pretty explicitly tied to PUD_SIZE.  But, that is a future cleanup.

-- 
Mike Kravetz