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Subject[patch] mm, thp: copying user pages must schedule on collapse
We have encountered need_resched warnings in __collapse_huge_page_copy()
while doing {clear,copy}_user_highpage() over HPAGE_PMD_NR source pages.

mm->mmap_sem is held for write, but the iteration is well bounded.

Reschedule as needed.

Signed-off-by: David Rientjes <rientjes@google.com>
---
mm/khugepaged.c | 7 +++----
1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -612,7 +612,8 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
spinlock_t *ptl)
{
pte_t *_pte;
- for (_pte = pte; _pte < pte+HPAGE_PMD_NR; _pte++) {
+ for (_pte = pte; _pte < pte + HPAGE_PMD_NR;
+ _pte++, page++, address += PAGE_SIZE) {
pte_t pteval = *_pte;
struct page *src_page;

@@ -651,9 +652,7 @@ static void __collapse_huge_page_copy(pte_t *pte, struct page *page,
spin_unlock(ptl);
free_page_and_swap_cache(src_page);
}
-
- address += PAGE_SIZE;
- page++;
+ cond_resched();
}
}

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