linux-kernel - [PATCH v3 08/66] mm/mmap: Use the maple tree for find_vma

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Date:   Tue, 5 Oct 2021 01:30:34 +0000
From:   Liam Howlett <liam.howlett@...cle.com>
To:     "maple-tree@...ts.infradead.org" <maple-tree@...ts.infradead.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...hat.com>,
        Douglas Gilbert <dgilbert@...erlog.com>
CC:     Song Liu <songliubraving@...com>,
        Davidlohr Bueso <dave@...olabs.net>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        David Rientjes <rientjes@...gle.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Rik van Riel <riel@...riel.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: [PATCH v3 08/66] mm/mmap: Use the maple tree for find_vma_prev()
 instead of the rbtree

From: "Liam R. Howlett" <Liam.Howlett@...cle.com>

Use the maple tree's advanced API and a maple state to walk the tree for
the entry at the address or the next vma, then use the maple state to
walk back one entry to find the previous entry.  Note, the advanced
maple tree interface does not handle the rcu locking.

Add kernel documentation comments for this API.

Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
---
 mm/mmap.c | 27 +++++++++++++++++----------
 1 file changed, 17 insertions(+), 10 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index fde3497a3c85..f6856bf65f2b 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2484,23 +2484,30 @@ struct vm_area_struct *find_vma(struct mm_struct *mm, unsigned long addr)
 }
 EXPORT_SYMBOL(find_vma);
 
-/*
- * Same as find_vma, but also return a pointer to the previous VMA in *pprev.
+/**
+ * find_vma_prev() - Find the VMA for a given address, or the next vma and
+ * set %pprev to the previous VMA, if any.
+ * @mm: The mm_struct to check
+ * @addr: The address
+ * @pprev: The pointer to set to the previous VMA
+ *
+ * Returns: The VMA associated with @addr, or the next vma.
+ * May return %NULL in the case of no vma at addr or above.
  */
 struct vm_area_struct *
 find_vma_prev(struct mm_struct *mm, unsigned long addr,
-			struct vm_area_struct **pprev)
+	      struct vm_area_struct **pprev)
 {
 	struct vm_area_struct *vma;
+	MA_STATE(mas, &mm->mm_mt, addr, addr);
 
-	vma = find_vma(mm, addr);
-	if (vma) {
-		*pprev = vma->vm_prev;
-	} else {
-		struct rb_node *rb_node = rb_last(&mm->mm_rb);
+	rcu_read_lock();
+	vma = mas_find(&mas, ULONG_MAX);
+	if (!vma)
+		mas_reset(&mas);
 
-		*pprev = rb_node ? rb_entry(rb_node, struct vm_area_struct, vm_rb) : NULL;
-	}
+	*pprev = mas_prev(&mas, 0);
+	rcu_read_unlock();
 	return vma;
 }
 
-- 
2.30.2