Re: [PATCH 1/3] mm/memory_hotplug: Allow an override for the memmap_on_memory param

From: David Hildenbrand
Date: Fri Jun 23 2023 - 08:36:14 EST

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In reply to: Aneesh Kumar K.V: "Re: [PATCH 1/3] mm/memory_hotplug: Allow an override for the memmap_on_memory param"
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On 23.06.23 10:40, Aneesh Kumar K.V wrote:

Vishal Verma <vishal.l.verma@xxxxxxxxx> writes:

For memory hotplug to consider MHP_MEMMAP_ON_MEMORY behavior, the
'memmap_on_memory' module parameter was a hard requirement.

In preparation for the dax/kmem driver to use memmap_on_memory
semantics, arrange for the module parameter check to be bypassed via the
appropriate mhp_flag.

Recall that the kmem driver could contribute huge amounts of hotplugged
memory originating from special purposes devices such as CXL memory
expanders. In some cases memmap_on_memory may be the /only/ way this new
memory can be hotplugged. Hence it makes sense for kmem to have a way to
force memmap_on_memory without depending on a module param, if all the
other conditions for it are met.

The only other user of this interface is acpi/acpi_memoryhotplug.c,
which only enables the mhp_flag if an initial
mhp_supports_memmap_on_memory() test passes. Maintain the existing
behavior and semantics for this by performing the initial check from
acpi without the MHP_MEMMAP_ON_MEMORY flag, so its decision falls back
to the module parameter.

Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
Cc: Len Brown <lenb@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Dave Jiang <dave.jiang@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Huang Ying <ying.huang@xxxxxxxxx>
Signed-off-by: Vishal Verma <vishal.l.verma@xxxxxxxxx>
---
include/linux/memory_hotplug.h | 2 +-
drivers/acpi/acpi_memhotplug.c | 2 +-
mm/memory_hotplug.c | 24 ++++++++++++++++--------
3 files changed, 18 insertions(+), 10 deletions(-)

diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 9fcbf5706595..c9ddcd3cad70 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -358,7 +358,7 @@ extern struct zone *zone_for_pfn_range(int online_type, int nid,
extern int arch_create_linear_mapping(int nid, u64 start, u64 size,
struct mhp_params *params);
void arch_remove_linear_mapping(u64 start, u64 size);
-extern bool mhp_supports_memmap_on_memory(unsigned long size);
+extern bool mhp_supports_memmap_on_memory(unsigned long size, mhp_t mhp_flags);
#endif /* CONFIG_MEMORY_HOTPLUG */
#endif /* __LINUX_MEMORY_HOTPLUG_H */
diff --git a/drivers/acpi/acpi_memhotplug.c b/drivers/acpi/acpi_memhotplug.c
index 24f662d8bd39..119d3bb49753 100644
--- a/drivers/acpi/acpi_memhotplug.c
+++ b/drivers/acpi/acpi_memhotplug.c
@@ -211,7 +211,7 @@ static int acpi_memory_enable_device(struct acpi_memory_device *mem_device)
if (!info->length)
continue;
- if (mhp_supports_memmap_on_memory(info->length))
+ if (mhp_supports_memmap_on_memory(info->length, 0))
mhp_flags |= MHP_MEMMAP_ON_MEMORY;
result = __add_memory(mgid, info->start_addr, info->length,
mhp_flags);
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 8e0fa209d533..bb3845830922 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -1283,15 +1283,21 @@ static int online_memory_block(struct memory_block *mem, void *arg)
return device_online(&mem->dev);
}
-bool mhp_supports_memmap_on_memory(unsigned long size)
+bool mhp_supports_memmap_on_memory(unsigned long size, mhp_t mhp_flags)
{
unsigned long nr_vmemmap_pages = size / PAGE_SIZE;
unsigned long vmemmap_size = nr_vmemmap_pages * sizeof(struct page);
unsigned long remaining_size = size - vmemmap_size;
/*
- * Besides having arch support and the feature enabled at runtime, we
- * need a few more assumptions to hold true:
+ * The MHP_MEMMAP_ON_MEMORY flag indicates a caller that wants to force
+ * memmap_on_memory (if other conditions are met), regardless of the
+ * module parameter. drivers/dax/kmem.c is an example, where large
+ * amounts of hotplug memory may come from, and the only option to
+ * successfully online all of it is to place the memmap on this memory.
+ *
+ * Besides having arch support and the feature enabled at runtime or
+ * via the mhp_flag, we need a few more assumptions to hold true:
*
* a) We span a single memory block: memory onlining/offlinin;g happens
* in memory block granularity. We don't want the vmemmap of online
@@ -1315,10 +1321,12 @@ bool mhp_supports_memmap_on_memory(unsigned long size)
* altmap as an alternative source of memory, and we do not exactly
* populate a single PMD.
*/
- return mhp_memmap_on_memory() &&
- size == memory_block_size_bytes() &&
- IS_ALIGNED(vmemmap_size, PMD_SIZE) &&
- IS_ALIGNED(remaining_size, (pageblock_nr_pages << PAGE_SHIFT));
+
+ if ((mhp_flags & MHP_MEMMAP_ON_MEMORY) || mhp_memmap_on_memory())
+ return size == memory_block_size_bytes() &&
+ IS_ALIGNED(vmemmap_size, PMD_SIZE) &&
+ IS_ALIGNED(remaining_size, (pageblock_nr_pages << PAGE_SHIFT));
+ return false;
}
/*
@@ -1375,7 +1383,7 @@ int __ref add_memory_resource(int nid, struct resource *res, mhp_t mhp_flags)
* Self hosted memmap array
*/
if (mhp_flags & MHP_MEMMAP_ON_MEMORY) {
- if (!mhp_supports_memmap_on_memory(size)) {
+ if (!mhp_supports_memmap_on_memory(size, mhp_flags)) {
ret = -EINVAL;
goto error;
}

I was working on enabling memmap_on_memory for ppc64 and came across
this. Can we do this as below?

commit d55eddf71032cad3e057d8fa4c61ad2b8e05aaa8
Author: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
Date: Fri Jun 23 12:11:31 2023 +0530

mm/hotplug: Allow to force enable memmap on memory
In some cases like DAX kmem, we want to enable memmap on memory
even if we have memory_hotplug.memmap_on_memory disabled. This
patch enables such usage. DAX kmem can use MHP_MEMMAP_ON_MEMORY
directly to request for memmap on memory.
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>

diff --git a/drivers/acpi/acpi_memhotplug.c b/drivers/acpi/acpi_memhotplug.c
index 24f662d8bd39..4d0096fc4cc2 100644
--- a/drivers/acpi/acpi_memhotplug.c
+++ b/drivers/acpi/acpi_memhotplug.c
@@ -211,8 +211,7 @@ static int acpi_memory_enable_device(struct acpi_memory_device *mem_device)
if (!info->length)
continue;
- if (mhp_supports_memmap_on_memory(info->length))
- mhp_flags |= MHP_MEMMAP_ON_MEMORY;
+ mhp_flags |= get_memmap_on_memory_flags();
result = __add_memory(mgid, info->start_addr, info->length,
mhp_flags);
diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
index 9fcbf5706595..f7f534084393 100644
--- a/include/linux/memory_hotplug.h
+++ b/include/linux/memory_hotplug.h
@@ -359,6 +359,13 @@ extern int arch_create_linear_mapping(int nid, u64 start, u64 size,
struct mhp_params *params);
void arch_remove_linear_mapping(u64 start, u64 size);
extern bool mhp_supports_memmap_on_memory(unsigned long size);
+bool mhp_memmap_on_memory(void);
#endif /* CONFIG_MEMORY_HOTPLUG */
+static inline unsigned long get_memmap_on_memory_flags(void)
+{
+ if (mhp_memmap_on_memory())
+ return MHP_MEMMAP_ON_MEMORY;
+ return 0;
+}
#endif /* __LINUX_MEMORY_HOTPLUG_H */
diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index eb18d1ac7e84..85d29909fd89 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -50,7 +50,7 @@ static bool memmap_on_memory __ro_after_init;
module_param(memmap_on_memory, bool, 0444);
MODULE_PARM_DESC(memmap_on_memory, "Enable memmap on memory for memory hotplug");
-static inline bool mhp_memmap_on_memory(void)
+bool mhp_memmap_on_memory(void)
{
return memmap_on_memory;
}
@@ -1316,10 +1316,9 @@ bool mhp_supports_memmap_on_memory(unsigned long size)
* altmap as an alternative source of memory, and we do not exactly
* populate a single PMD.
*/
- return mhp_memmap_on_memory() &&
- size == memory_block_size_bytes() &&
- IS_ALIGNED(vmemmap_size, PMD_SIZE) &&
- IS_ALIGNED(remaining_size, (pageblock_nr_pages << PAGE_SHIFT));
+ return size == memory_block_size_bytes() &&
+ IS_ALIGNED(vmemmap_size, PMD_SIZE) &&
+ IS_ALIGNED(remaining_size, (pageblock_nr_pages << PAGE_SHIFT));
}
/*

Any forced enablement will have to cleanly handle try_remove_memory() as well.

memmap_on_memory needs a doc update then, and even the "forced enablement" has to still be explicitly enabled by the admin.

... but I'm still not convinced that memmap_on_memory should be overridden. Needs good justification.

--
Cheers,

David / dhildenb

Next message: Bagas Sanjaya: "Fwd: kernel fault on hibernation: get_zeroed_page/swsusp_write"
Previous message: Krzysztof Kozlowski: "Re: [PATCH 2/5] scsi: dt-bindings: ufs: qcom: Add compatible for sm6115 and sm6125"
In reply to: Aneesh Kumar K.V: "Re: [PATCH 1/3] mm/memory_hotplug: Allow an override for the memmap_on_memory param"
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