Re: [PATCH v1 1/2] drivers/base/memory: don't store phys_device in memory blocks

Michal Hocko
2021-02-01T16:00:08Z

On Mon 01-02-21 11:51:57, David Hildenbrand wrote:
> 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 devices
> 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

Thanks for an excellent changelog!

> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Dave Hansen <dave.hansen@intel.com>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: "Rafael J. Wysocki" <rafael@kernel.org>
> Cc: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
> Cc: Ilya Dryomov <idryomov@gmail.com>
> Cc: Vaibhav Jain <vaibhav@linux.ibm.com>
> Cc: Tom Rix <trix@redhat.com>
> Cc: Geert Uytterhoeven <geert+renesas@glider.be>
> Cc: linux-doc@vger.kernel.org
> Signed-off-by: David Hildenbrand <david@redhat.com>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
> .../ABI/testing/sysfs-devices-memory | 5 ++--
> .../admin-guide/mm/memory-hotplug.rst | 4 ++--
> drivers/base/memory.c | 23 ++++++++-----------
> include/linux/memory.h | 3 +--
> 4 files changed, 15 insertions(+), 20 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@us.ibm.com>
> 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..16959d339172 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;
> @@ -589,7 +585,6 @@ 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
>

--
Michal Hocko
SUSE Labs