Re: [PATCH v6 1/2] mm: migration: fix migration of huge PMD shared pages

On Mon, Aug 27, 2018 at 09:46:45AM +0200, Michal Hocko wrote:

On Fri 24-08-18 11:08:24, Mike Kravetz wrote:

quoted

On 08/24/2018 01:41 AM, Michal Hocko wrote:

quoted

On Thu 23-08-18 13:59:16, Mike Kravetz wrote:

Acked-by: Michal Hocko <mhocko@suse.com>

One nit below.

[...]

quoted

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 3103099f64fd..a73c5728e961 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c

@@ -4548,6 +4548,9 @@ static unsigned long page_table_shareable(struct vm_area_struct *svma,
 	return saddr;
 }
 
+#define _range_in_vma(vma, start, end) \
+	((vma)->vm_start <= (start) && (end) <= (vma)->vm_end)
+

static inline please. Macros and potential side effects on given
arguments are just not worth the risk. I also think this is something
for more general use. We have that pattern at many places. So I would
stick that to linux/mm.h

Thanks Michal,

Here is an updated patch which does as you suggest above.

[...]

quoted

@@ -1409,6 +1419,32 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
 		subpage = page - page_to_pfn(page) + pte_pfn(*pvmw.pte);
 		address = pvmw.address;
 
+		if (PageHuge(page)) {
+			if (huge_pmd_unshare(mm, &address, pvmw.pte)) {
+				/*
+				 * huge_pmd_unshare unmapped an entire PMD
+				 * page.  There is no way of knowing exactly
+				 * which PMDs may be cached for this mm, so
+				 * we must flush them all.  start/end were
+				 * already adjusted above to cover this range.
+				 */
+				flush_cache_range(vma, start, end);
+				flush_tlb_range(vma, start, end);
+				mmu_notifier_invalidate_range(mm, start, end);
+
+				/*
+				 * The ref count of the PMD page was dropped
+				 * which is part of the way map counting
+				 * is done for shared PMDs.  Return 'true'
+				 * here.  When there is no other sharing,
+				 * huge_pmd_unshare returns false and we will
+				 * unmap the actual page and drop map count
+				 * to zero.
+				 */
+				page_vma_mapped_walk_done(&pvmw);
+				break;
+			}

This still calls into notifier while holding the ptl lock. Either I am
missing something or the invalidation is broken in this loop (not also
for other invalidations).

mmu_notifier_invalidate_range() is done with pt lock held only the start
and end versions need to happen outside pt lock.

Cheers,
Jerome