Subject: [PATCH mm,net-next 1/3] mm: Refactor insert_page to prepare for batched-lock insert.

From: Arjun Roy <[email-masked]>
Date: Fri, 10 Jan 2020 16:28:47 -0800

Add helper methods for vm_insert_page()/insert_page() to prepare for
vm_insert_pages(), which batch-inserts pages to reduce spinlock
operations when inserting multiple consecutive pages into the user
page table.

The intention of this patch-set is to reduce atomic ops for
tcp zerocopy receives, which normally hits the same spinlock multiple
times consecutively.

Signed-off-by: Arjun Roy <[email-masked]>
Signed-off-by: Eric Dumazet <[email-masked]>
Signed-off-by: Soheil Hassas Yeganeh <[email-masked]>

---
 mm/memory.c | 41 ++++++++++++++++++++++++-----------------
 1 file changed, 24 insertions(+), 17 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index 7c6e19bdc428..7e23a9275386 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -1693,6 +1693,27 @@ pte_t *__get_locked_pte(struct mm_struct *mm, unsigned long addr,
 	return pte_alloc_map_lock(mm, pmd, addr, ptl);
 }
 
+static int validate_page_before_insert(struct page *page)
+{
+	if (PageAnon(page) || PageSlab(page))
+		return -EINVAL;
+	flush_dcache_page(page);
+	return 0;
+}
+
+static int insert_page_into_pte_locked(struct mm_struct *mm, pte_t *pte,
+			unsigned long addr, struct page *page, pgprot_t prot)
+{
+	if (!pte_none(*pte))
+		return -EBUSY;
+	/* Ok, finally just insert the thing.. */
+	get_page(page);
+	inc_mm_counter_fast(mm, mm_counter_file(page));
+	page_add_file_rmap(page, false);
+	set_pte_at(mm, addr, pte, mk_pte(page, prot));
+	return 0;
+}
+
 /*
  * This is the old fallback for page remapping.
  *
@@ -1708,28 +1729,14 @@ static int insert_page(struct vm_area_struct *vma, unsigned long addr,
 	pte_t *pte;
 	spinlock_t *ptl;
 
-	retval = -EINVAL;
-	if (PageAnon(page) || PageSlab(page))
+	retval = validate_page_before_insert(page);
+	if (retval)
 		goto out;
 	retval = -ENOMEM;
-	flush_dcache_page(page);
 	pte = get_locked_pte(mm, addr, &ptl);
 	if (!pte)
 		goto out;
-	retval = -EBUSY;
-	if (!pte_none(*pte))
-		goto out_unlock;
-
-	/* Ok, finally just insert the thing.. */
-	get_page(page);
-	inc_mm_counter_fast(mm, mm_counter_file(page));
-	page_add_file_rmap(page, false);
-	set_pte_at(mm, addr, pte, mk_pte(page, prot));
-
-	retval = 0;
-	pte_unmap_unlock(pte, ptl);
-	return retval;
-out_unlock:
+	retval = insert_page_into_pte_locked(mm, pte, addr, page, prot);
 	pte_unmap_unlock(pte, ptl);
 out:
 	return retval;
-- 
2.25.0.rc1.283.g88dfdc4193-goog