linux-kernel - [PATCH 20/28] mm/mmap: Change __do_munmap() to avoid unnecessary lookups.

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Date:   Thu, 10 Dec 2020 12:03:54 -0500
From:   "Liam R. Howlett" <Liam.Howlett@...cle.com>
To:     maple-tree@...ts.infradead.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Cc:     Andrew Morton <akpm@...gle.com>, Song Liu <songliubraving@...com>,
        Davidlohr Bueso <dave@...olabs.net>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Jerome Glisse <jglisse@...hat.com>,
        David Rientjes <rientjes@...gle.com>,
        Axel Rasmussen <axelrasmussen@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: [PATCH 20/28] mm/mmap: Change __do_munmap() to avoid unnecessary lookups.

As there is no longer a vmacache, find_vma() is more expensive and so
avoid doing them

Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
---
 mm/mmap.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index c3ac4d6f970d3..15616f105d051 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2720,7 +2720,6 @@ int __do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
 	if (!vma)
 		return 0;
 
-	prev = vma->vm_prev;
 	/* we have start < vma->vm_end  */
 
 	/*
@@ -2744,16 +2743,24 @@ int __do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
 		if (error)
 			return error;
 		prev = vma;
+		vma = vma_next(mm, prev);
+	} else {
+		prev = vma->vm_prev;
 	}
 
+	if (vma->vm_end >= end)
+		last = vma;
+	else
+		last = find_vma_intersection(mm, end - 1, end);
+
 	/* Does it split the last one? */
-	last = find_vma(mm, end);
-	if (last && end > last->vm_start) {
+	if (last && end < last->vm_end) {
 		int error = __split_vma(mm, last, end, 1);
 		if (error)
 			return error;
+		vma = vma_next(mm, prev);
 	}
-	vma = vma_next(mm, prev);
+
 
 	if (unlikely(uf)) {
 		/*
@@ -2766,6 +2773,7 @@ int __do_munmap(struct mm_struct *mm, unsigned long start, size_t len,
 		 * failure that it's not worth optimizing it for.
 		 */
 		int error = userfaultfd_unmap_prep(vma, start, end, uf);
+
 		if (error)
 			return error;
 	}
-- 
2.28.0