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

From: Yan Zhao
Date: Tue Aug 08 2023 - 12:43:30 EST


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