linux-kernel - [PATCH v4 17/66] mmap: Change zeroing of maple tree in __vma

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Message-ID: <20211201142918.921493-18-Liam.Howlett@oracle.com>
Date:   Wed, 1 Dec 2021 14:29:57 +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>
CC:     Song Liu <songliubraving@...com>,
        Davidlohr Bueso <dave@...olabs.net>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Matthew Wilcox <willy@...radead.org>,
        Laurent Dufour <ldufour@...ux.ibm.com>,
        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>,
        Michel Lespinasse <walken.cr@...il.com>,
        Jerome Glisse <jglisse@...hat.com>,
        Minchan Kim <minchan@...gle.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Rom Lemarchand <romlem@...gle.com>,
        Liam Howlett <liam.howlett@...cle.com>
Subject: [PATCH v4 17/66] 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 93ed19b2c6ce..c5f92666d145 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -615,6 +615,7 @@ 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;
@@ -740,25 +741,29 @@ 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_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