[RFC PATCH 2/3] mm: don't set PROT_NONE to maybe-dma-pinned pages for NUMA-migrate purpose

[Yan Zhao]

Don't set PROT_NONE for exclusive anonymas and maybe-dma-pinned pages for
NUMA migration purpose.

For exclusive anonymas and page_maybe_dma_pinned() pages, NUMA-migration
will eventually drop migration of those pages in try_to_migrate_one().
(i.e. after -EBUSY returned in page_try_share_anon_rmap()).

So, skip setting PROT_NONE to those kind of pages earlier in
change_protection_range() phase to avoid later futile page faults,
detections, and restoration to original PTEs/PMDs.

Signed-off-by: Yan Zhao <yan.y.zhao@xxxxxxxxx>
---
 mm/huge_memory.c | 5 +++++
 mm/mprotect.c    | 5 +++++
 2 files changed, 10 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index eb3678360b97..a71cf686e3b2 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1875,6 +1875,11 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
 			goto unlock;
 
 		page = pmd_page(*pmd);
+
+		if (PageAnon(page) && PageAnonExclusive(page) &&
+		    page_maybe_dma_pinned(page))
+			goto unlock;
+
 		toptier = node_is_toptier(page_to_nid(page));
 		/*
 		 * Skip scanning top tier node if normal numa
diff --git a/mm/mprotect.c b/mm/mprotect.c
index cb99a7d66467..a1f63df34b86 100644
--- a/mm/mprotect.c
+++ b/mm/mprotect.c
@@ -146,6 +146,11 @@ static long change_pte_range(struct mmu_gather *tlb,
 				nid = page_to_nid(page);
 				if (target_node == nid)
 					continue;
+
+				if (PageAnon(page) && PageAnonExclusive(page) &&
+				    page_maybe_dma_pinned(page))
+					continue;
+
 				toptier = node_is_toptier(nid);
 
 				/*
-- 
2.17.1