linux-kernel - [PATCH v3 12/66] mmap: Change zeroing of maple tree in __vma

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Date:   Tue, 5 Oct 2021 01:30:36 +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 12/66] mmap: Change zeroing of maple tree in __vma_adjust

Only write to the maple tree if we are not inserting or the insert isn't
going to overwrite the area to clear.  This avoids spanning writes and
node coealescing when unnecessary.

Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
---
 mm/mmap.c | 21 +++++++++++++--------
 1 file changed, 13 insertions(+), 8 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index c51d739d7411..9f047204fa93 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -626,6 +626,7 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
 	bool vma_changed = false;
 	long adjust_next = 0;
 	int remove_next = 0;
+	unsigned long old_start;
 
 	if (next && !insert) {
 		struct vm_area_struct *exporter = NULL, *importer = NULL;
@@ -751,25 +752,29 @@ int __vma_adjust(struct vm_area_struct *vma, unsigned long start,
 			vma_interval_tree_remove(next, root);
 	}
 
+	old_start = vma->vm_start;
 	if (start != vma->vm_start) {
-		if (vma->vm_start < start)
-			vma_mt_szero(mm, vma->vm_start, start);
-		else
-			vma_changed = true;
+		vma_changed = true;
 		vma->vm_start = start;
 	}
 	if (end != vma->vm_end) {
-		if (vma->vm_end > end)
-			vma_mt_szero(mm, end, vma->vm_end);
-		else
+		if (vma->vm_end > end) {
+			if (!insert || (insert && (insert->vm_start != end)))
+				vma_mt_szero(mm, end, vma->vm_end);
+		} else
 			vma_changed = true;
 		vma->vm_end = end;
 		if (!next)
 			mm->highest_vm_end = vm_end_gap(vma);
 	}
 
-	if (vma_changed)
+	if (vma_changed) {
 		vma_mt_store(mm, vma);
+		if (old_start < start) {
+			if (insert && (insert->vm_start != old_start))
+				vma_mt_szero(mm, old_start, start);
+		}
+	}
 
 	vma->vm_pgoff = pgoff;
 	if (adjust_next) {
-- 
2.30.2