[PATCH v2 1/2] drivers/base/memory: don't store phys_device in memory blocks
From: David Hildenbrand
Date: Mon Feb 01 2021 - 13:19:58 EST
No need to store the value for each and every memory block, as we can
easily query the value at runtime. Reshuffle the members to optimize the
memory layout. Also, let's clarify what the interface once was used for
and why it's legacy nowadays.
"phys_device" was used on s390x in older versions of lsmem[2]/chmem[3],
back when they were still part of s390x-tools. They were later replaced
by the variants in linux-utils. For example, RHEL6 and RHEL7 contain
lsmem/chmem from s390-utils. RHEL8 switched to versions from util-linux
on s390x [4].
"phys_device" was added with sysfs support for memory hotplug in
commit 3947be1969a9 ("[PATCH] memory hotplug: sysfs and add/remove
functions") in 2005. It always returned 0.
s390x started returning something != 0 on some setups (if sclp.rzm is
set by HW) in 2010 via commit 57b552ba0b2f ("memory hotplug/s390: set
phys_device").
For s390x, it allowed for identifying which memory block devices belong
to the same storage increment (RZM). Only if all memory block devices
comprising a single storage increment were offline, the memory could
actually be removed in the hypervisor.
Since commit e5d709bb5fb7 ("s390/memory hotplug: provide
memory_block_size_bytes() function") in 2013 a memory block device
spans at least one storage increment - which is why the interface isn't
really helpful/used anymore (except by old lsmem/chmem tools).
There were once RFC patches to make use of "phys_device" in ACPI context;
however, the underlying problem could be solved using different
interfaces [1].
[1] https://patchwork.kernel.org/patch/2163871/
[2] https://github.com/ibm-s390-tools/s390-tools/blob/v2.1.0/zconf/lsmem
[3] https://github.com/ibm-s390-tools/s390-tools/blob/v2.1.0/zconf/chmem
[4] https://bugzilla.redhat.com/show_bug.cgi?id=1504134
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Gerald Schaefer <gerald.schaefer@xxxxxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
Cc: Mauro Carvalho Chehab <mchehab+huawei@xxxxxxxxxx>
Cc: Ilya Dryomov <idryomov@xxxxxxxxx>
Cc: Vaibhav Jain <vaibhav@xxxxxxxxxxxxx>
Cc: Tom Rix <trix@xxxxxxxxxx>
Cc: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
Cc: linux-doc@xxxxxxxxxxxxxxx
Signed-off-by: David Hildenbrand <david@xxxxxxxxxx>
---
.../ABI/testing/sysfs-devices-memory | 5 ++--
.../admin-guide/mm/memory-hotplug.rst | 4 +--
drivers/base/memory.c | 25 +++++++------------
include/linux/memory.h | 3 +--
4 files changed, 15 insertions(+), 22 deletions(-)
diff --git a/Documentation/ABI/testing/sysfs-devices-memory b/Documentation/ABI/testing/sysfs-devices-memory
index 246a45b96d22..58dbc592bc57 100644
--- a/Documentation/ABI/testing/sysfs-devices-memory
+++ b/Documentation/ABI/testing/sysfs-devices-memory
@@ -26,8 +26,9 @@ Date: September 2008
Contact: Badari Pulavarty <pbadari@xxxxxxxxxx>
Description:
The file /sys/devices/system/memory/memoryX/phys_device
- is read-only and is designed to show the name of physical
- memory device. Implementation is currently incomplete.
+ is read-only; it is a legacy interface only ever used on s390x
+ to expose the covered storage increment.
+Users: Legacy s390-tools lsmem/chmem
What: /sys/devices/system/memory/memoryX/phys_index
Date: September 2008
diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst
index 5c4432c96c4b..245739f55ac7 100644
--- a/Documentation/admin-guide/mm/memory-hotplug.rst
+++ b/Documentation/admin-guide/mm/memory-hotplug.rst
@@ -160,8 +160,8 @@ Under each memory block, you can see 5 files:
"online_movable", "online", "offline" command
which will be performed on all sections in the block.
-``phys_device`` read-only: designed to show the name of physical memory
- device. This is not well implemented now.
+``phys_device`` read-only: legacy interface only ever used on s390x to
+ expose the covered storage increment.
``removable`` read-only: contains an integer value indicating
whether the memory block is removable or not
removable. A value of 1 indicates that the memory
diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index 901e379676be..f35298425575 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -290,20 +290,20 @@ static ssize_t state_store(struct device *dev, struct device_attribute *attr,
}
/*
- * phys_device is a bad name for this. What I really want
- * is a way to differentiate between memory ranges that
- * are part of physical devices that constitute
- * a complete removable unit or fru.
- * i.e. do these ranges belong to the same physical device,
- * s.t. if I offline all of these sections I can then
- * remove the physical device?
+ * Legacy interface that we cannot remove: s390x exposes the storage increment
+ * covered by a memory block, allowing for identifying which memory blocks
+ * comprise a storage increment. Since a memory block spans complete
+ * storage increments nowadays, this interface is basically unused. Other
+ * archs never exposed != 0.
*/
static ssize_t phys_device_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
struct memory_block *mem = to_memory_block(dev);
+ unsigned long start_pfn = section_nr_to_pfn(mem->start_section_nr);
- return sysfs_emit(buf, "%d\n", mem->phys_device);
+ return sysfs_emit(buf, "%d\n",
+ arch_get_memory_phys_device(start_pfn));
}
#ifdef CONFIG_MEMORY_HOTREMOVE
@@ -488,11 +488,7 @@ static DEVICE_ATTR_WO(soft_offline_page);
static DEVICE_ATTR_WO(hard_offline_page);
#endif
-/*
- * Note that phys_device is optional. It is here to allow for
- * differentiation between which *physical* devices each
- * section belongs to...
- */
+/* See phys_device_show(). */
int __weak arch_get_memory_phys_device(unsigned long start_pfn)
{
return 0;
@@ -574,7 +570,6 @@ int register_memory(struct memory_block *memory)
static int init_memory_block(unsigned long block_id, unsigned long state)
{
struct memory_block *mem;
- unsigned long start_pfn;
int ret = 0;
mem = find_memory_block_by_id(block_id);
@@ -588,8 +583,6 @@ static int init_memory_block(unsigned long block_id, unsigned long state)
mem->start_section_nr = block_id * sections_per_block;
mem->state = state;
- start_pfn = section_nr_to_pfn(mem->start_section_nr);
- mem->phys_device = arch_get_memory_phys_device(start_pfn);
mem->nid = NUMA_NO_NODE;
ret = register_memory(mem);
diff --git a/include/linux/memory.h b/include/linux/memory.h
index 439a89e758d8..4da95e684e20 100644
--- a/include/linux/memory.h
+++ b/include/linux/memory.h
@@ -27,9 +27,8 @@ struct memory_block {
unsigned long start_section_nr;
unsigned long state; /* serialized by the dev->lock */
int online_type; /* for passing data to online routine */
- int phys_device; /* to which fru does this belong? */
- struct device dev;
int nid; /* NID for this memory block */
+ struct device dev;
};
int arch_get_memory_phys_device(unsigned long start_pfn);
--
2.29.2