linux-kernel - [PATCH 6/8] dax/kmem: add online/offline helper functions

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Message-ID: <20260114085201.3222597-7-gourry@gourry.net>
Date: Wed, 14 Jan 2026 03:51:58 -0500
From: Gregory Price <gourry@...rry.net>
To: linux-mm@...ck.org
Cc: linux-cxl@...r.kernel.org,
	nvdimm@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	virtualization@...ts.linux.dev,
	kernel-team@...a.com,
	dan.j.williams@...el.com,
	vishal.l.verma@...el.com,
	dave.jiang@...el.com,
	david@...nel.org,
	mst@...hat.com,
	jasowang@...hat.com,
	xuanzhuo@...ux.alibaba.com,
	eperezma@...hat.com,
	osalvador@...e.de,
	akpm@...ux-foundation.org
Subject: [PATCH 6/8] dax/kmem: add online/offline helper functions

Add helper functions for onlining and offlining memory ranges:

  - dax_kmem_do_online(): online memory with specified type (MMOP_ONLINE
    or MMOP_ONLINE_MOVABLE) using online_memory_range()
  - dax_kmem_do_offline(): offline memory using offline_memory()

These helpers use the memory hotplug APIs from the memory_hotplug
refactoring and will be used by the upcoming sysfs interface to allow
userspace control over memory state transitions.

No functional change as these helpers are not called yet.

Signed-off-by: Gregory Price <gourry@...rry.net>
---
 drivers/dax/kmem.c | 103 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 103 insertions(+)

diff --git a/drivers/dax/kmem.c b/drivers/dax/kmem.c
index 5225f2bf0b2a..30429f2d5a67 100644
--- a/drivers/dax/kmem.c
+++ b/drivers/dax/kmem.c
@@ -190,6 +190,109 @@ static int dax_kmem_do_hotremove(struct dev_dax *dev_dax,
 }
 #endif /* CONFIG_MEMORY_HOTREMOVE */
 
+/**
+ * dax_kmem_do_online - online memory blocks for dax kmem device
+ * @dev_dax: the dev_dax instance
+ * @data: the dax_kmem_data structure with resource tracking
+ * @online_type: MMOP_ONLINE or MMOP_ONLINE_MOVABLE
+ *
+ * Onlines all ranges in the dev_dax region with the specified online type.
+ * On partial failure, previously onlined ranges are rolled back to offline.
+ *
+ * Returns 0 on success, negative error code on failure.
+ */
+static int dax_kmem_do_online(struct dev_dax *dev_dax,
+			      struct dax_kmem_data *data, int online_type)
+{
+	int i, j, rc;
+
+	for (i = 0; i < dev_dax->nr_range; i++) {
+		struct range range;
+
+		rc = dax_kmem_range(dev_dax, i, &range);
+		if (rc)
+			continue;
+
+		if (!data->res[i])
+			continue;
+
+		rc = online_memory_range(range.start, range_len(&range),
+					 online_type);
+		if (rc)
+			goto rollback;
+	}
+
+	return 0;
+
+rollback:
+	/* Rollback previously onlined ranges */
+	for (j = 0; j < i; j++) {
+		struct range range;
+
+		if (dax_kmem_range(dev_dax, j, &range))
+			continue;
+
+		if (!data->res[j])
+			continue;
+
+		/* Best effort rollback - ignore failures */
+		offline_memory(range.start, range_len(&range));
+	}
+	return rc;
+}
+
+/**
+ * dax_kmem_do_offline - offline memory blocks for dax kmem device
+ * @dev_dax: the dev_dax instance
+ * @data: the dax_kmem_data structure with resource tracking
+ *
+ * Offlines all ranges in the dev_dax region.
+ * On partial failure, previously offlined ranges are rolled back to online.
+ *
+ * Returns 0 on success, negative error code on failure.
+ */
+static int dax_kmem_do_offline(struct dev_dax *dev_dax,
+			       struct dax_kmem_data *data)
+{
+	int i, j, rc;
+
+	for (i = 0; i < dev_dax->nr_range; i++) {
+		struct range range;
+
+		rc = dax_kmem_range(dev_dax, i, &range);
+		if (rc)
+			continue;
+
+		if (!data->res[i])
+			continue;
+
+		rc = offline_memory(range.start, range_len(&range));
+		if (rc)
+			goto rollback;
+	}
+
+	return 0;
+
+rollback:
+	/*
+	 * Rollback previously offlined ranges. Use MMOP_ONLINE as a safe
+	 * default - the original online type is not tracked per-range.
+	 */
+	for (j = 0; j < i; j++) {
+		struct range range;
+
+		if (dax_kmem_range(dev_dax, j, &range))
+			continue;
+
+		if (!data->res[j])
+			continue;
+
+		/* Best effort rollback - ignore failures */
+		online_memory_range(range.start, range_len(&range), MMOP_ONLINE);
+	}
+	return rc;
+}
+
 static int dev_dax_kmem_probe(struct dev_dax *dev_dax)
 {
 	struct device *dev = &dev_dax->dev;
-- 
2.52.0