Hi Robin,

On Mon 27 Nov 2017, 15:33, Robin Murphy wrote:

On 23/11/17 11:14, Andrea Reale wrote:

quoted

Adding a "remove" sysfs handle that can be used to trigger
memory hotremove manually, exactly simmetrically with
what happens with the "probe" device for hot-add.

This is usueful for architecture that do not rely on
ACPI for memory hot-remove.

Is there a real-world use-case for this, or is it mostly just a handy
development feature?

as I was saying in a response to your previous message, in our use
case remove events are triggered by software. Besides our use case,
yes, it is mostly just a handy develeopment feature AFAICT.

quoted

Signed-off-by: Andrea Reale <redacted>
Signed-off-by: Maciej Bielski <redacted>
---
 drivers/base/memory.c | 34 +++++++++++++++++++++++++++++++++-
 1 file changed, 33 insertions(+), 1 deletion(-)

diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index 1d60b58..8ccb67c 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c

@@ -530,7 +530,36 @@ memory_probe_store(struct device *dev, struct device_attribute *attr,
 }
 static DEVICE_ATTR(probe, S_IWUSR, NULL, memory_probe_store);
-#endif
+
+#ifdef CONFIG_MEMORY_HOTREMOVE
+static ssize_t
+memory_remove_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t count)
+{
+	u64 phys_addr;
+	int nid, ret;
+	unsigned long pages_per_block = PAGES_PER_SECTION * sections_per_block;
+
+	ret = kstrtoull(buf, 0, &phys_addr);
+	if (ret)
+		return ret;
+
+	if (phys_addr & ((pages_per_block << PAGE_SHIFT) - 1))
+		return -EINVAL;
+
+	nid = memory_add_physaddr_to_nid(phys_addr);

This call looks a bit odd, since you're not doing a memory add. In fact, any
memory being removed should already be fully known-about, so AFAICS it
should be simple to get everything you need to know (including potentially
the online status as mentioned earlier), through 'normal' methods, e.g.
page_to_nid() or similar.

Makes sense. Suggestion noted, thanks.

Robin.

quoted

+	ret = lock_device_hotplug_sysfs();
+	if (ret)
+		return ret;
+
+	remove_memory(nid, phys_addr,
+			 MIN_MEMORY_BLOCK_SIZE * sections_per_block);
+	unlock_device_hotplug();
+	return count;
+}
+static DEVICE_ATTR(remove, S_IWUSR, NULL, memory_remove_store);
+#endif /* CONFIG_MEMORY_HOTREMOVE */
+#endif /* CONFIG_ARCH_MEMORY_PROBE */
 #ifdef CONFIG_MEMORY_FAILURE
 /*

@@ -790,6 +819,9 @@ bool is_memblock_offlined(struct memory_block *mem)
 static struct attribute *memory_root_attrs[] = {
 #ifdef CONFIG_ARCH_MEMORY_PROBE
 	&dev_attr_probe.attr,
+#ifdef CONFIG_MEMORY_HOTREMOVE
+	&dev_attr_remove.attr,
+#endif
 #endif
 #ifdef CONFIG_MEMORY_FAILURE