KVM: Don't pre-reserve xarray entries when storing empty/NULL attributesgrafted

Skip the xarray reservation loop when clearing all memory attributes, as
storing NULL only erases the entry and never needs to allocate, so no
reservation (and no cleanup of a failed one) is required in that case.

Suggested-by: Sean Christopherson <seanjc@google.com>
Cc: David Ballesteros <davimaba.v@proton.me>
Signed-off-by: Zeng Chi <zengchi@kylinos.cn>
Link: https://patch.msgid.link/20260921102442.1232375-1-zeng_chi911@163.com
[sean: split to separate patch]
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 82 insertions, 0 deletions

diff --git a/drivers/md/dm-io-tracker.h b/drivers/md/dm-io-tracker.h
new file mode 100644
index 000000000..bea1ca118
--- /dev/null
+++ b/drivers/md/dm-io-tracker.h
@@ -0,0 +1,82 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2021 Red Hat, Inc. All rights reserved.
+ *
+ * This file is released under the GPL.
+ */
+
+#ifndef DM_IO_TRACKER_H
+#define DM_IO_TRACKER_H
+
+#include <linux/jiffies.h>
+
+struct dm_io_tracker {
+	spinlock_t lock;
+
+	/*
+	 * Sectors of in-flight IO.
+	 */
+	sector_t in_flight;
+
+	/*
+	 * The time, in jiffies, when this device became idle
+	 * (if it is indeed idle).
+	 */
+	unsigned long idle_time;
+	unsigned long last_update_time;
+};
+
+static inline void dm_iot_init(struct dm_io_tracker *iot)
+{
+	spin_lock_init(&iot->lock);
+	iot->in_flight = 0ul;
+	iot->idle_time = 0ul;
+	iot->last_update_time = jiffies;
+}
+
+static inline bool dm_iot_idle_for(struct dm_io_tracker *iot, unsigned long j)
+{
+	bool r = false;
+
+	spin_lock_irq(&iot->lock);
+	if (!iot->in_flight)
+		r = time_after(jiffies, iot->idle_time + j);
+	spin_unlock_irq(&iot->lock);
+
+	return r;
+}
+
+static inline unsigned long dm_iot_idle_time(struct dm_io_tracker *iot)
+{
+	unsigned long r = 0;
+
+	spin_lock_irq(&iot->lock);
+	if (!iot->in_flight)
+		r = jiffies - iot->idle_time;
+	spin_unlock_irq(&iot->lock);
+
+	return r;
+}
+
+static inline void dm_iot_io_begin(struct dm_io_tracker *iot, sector_t len)
+{
+	spin_lock_irq(&iot->lock);
+	iot->in_flight += len;
+	spin_unlock_irq(&iot->lock);
+}
+
+static inline void dm_iot_io_end(struct dm_io_tracker *iot, sector_t len)
+{
+	unsigned long flags;
+
+	if (!len)
+		return;
+
+	spin_lock_irqsave(&iot->lock, flags);
+	iot->in_flight -= len;
+	if (!iot->in_flight)
+		iot->idle_time = jiffies;
+	spin_unlock_irqrestore(&iot->lock, flags);
+}
+
+#endif