linux-toradex.git/Documentation/ABI/testing/sysfs-devices-memory, branch v6.15

Document/kexec: generalize crash hotplug description

2024-09-02T03:43:37+00:00

Commit 79365026f869 ("crash: add a new kexec flag for hotplug support")
generalizes the crash hotplug support to allow architectures to update
multiple kexec segments on CPU/Memory hotplug and not just elfcorehdr. 
Therefore, update the relevant kernel documentation to reflect the same.

No functional change.

Link: https://lkml.kernel.org/r/20240812041651.703156-1-sourabhjain@linux.ibm.com
Signed-off-by: Sourabh Jain 
Reviewed-by: Petr Tesarik 
Acked-by: Baoquan He 
Cc: Hari Bathini 
Cc: Petr Tesarik 
Cc: Sourabh Jain 
Cc: Jonathan Corbet 
Signed-off-by: Andrew Morton

crash: memory and CPU hotplug sysfs attributes

2023-08-24T23:25:14+00:00

Introduce the crash_hotplug attribute for memory and CPUs for use by
userspace.  These attributes directly facilitate the udev rule for
managing userspace re-loading of the crash kernel upon hot un/plug
changes.

For memory, expose the crash_hotplug attribute to the
/sys/devices/system/memory directory.  For example:

 # udevadm info --attribute-walk /sys/devices/system/memory/memory81
  looking at device '/devices/system/memory/memory81':
    KERNEL=="memory81"
    SUBSYSTEM=="memory"
    DRIVER==""
    ATTR{online}=="1"
    ATTR{phys_device}=="0"
    ATTR{phys_index}=="00000051"
    ATTR{removable}=="1"
    ATTR{state}=="online"
    ATTR{valid_zones}=="Movable"

  looking at parent device '/devices/system/memory':
    KERNELS=="memory"
    SUBSYSTEMS==""
    DRIVERS==""
    ATTRS{auto_online_blocks}=="offline"
    ATTRS{block_size_bytes}=="8000000"
    ATTRS{crash_hotplug}=="1"

For CPUs, expose the crash_hotplug attribute to the
/sys/devices/system/cpu directory. For example:

 # udevadm info --attribute-walk /sys/devices/system/cpu/cpu0
  looking at device '/devices/system/cpu/cpu0':
    KERNEL=="cpu0"
    SUBSYSTEM=="cpu"
    DRIVER=="processor"
    ATTR{crash_notes}=="277c38600"
    ATTR{crash_notes_size}=="368"
    ATTR{online}=="1"

  looking at parent device '/devices/system/cpu':
    KERNELS=="cpu"
    SUBSYSTEMS==""
    DRIVERS==""
    ATTRS{crash_hotplug}=="1"
    ATTRS{isolated}==""
    ATTRS{kernel_max}=="8191"
    ATTRS{nohz_full}=="  (null)"
    ATTRS{offline}=="4-7"
    ATTRS{online}=="0-3"
    ATTRS{possible}=="0-7"
    ATTRS{present}=="0-3"

With these sysfs attributes in place, it is possible to efficiently
instruct the udev rule to skip crash kernel reloading for kernels
configured with crash hotplug support.

For example, the following is the proposed udev rule change for RHEL
system 98-kexec.rules (as the first lines of the rule file):

 # The kernel updates the crash elfcorehdr for CPU and memory changes
 SUBSYSTEM=="cpu", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end"
 SUBSYSTEM=="memory", ATTRS{crash_hotplug}=="1", GOTO="kdump_reload_end"

When examined in the context of 98-kexec.rules, the above rules test if
crash_hotplug is set, and if so, the userspace initiated
unload-then-reload of the crash kernel is skipped.

CPU and memory checks are separated in accordance with CONFIG_HOTPLUG_CPU
and CONFIG_MEMORY_HOTPLUG kernel config options.  If an architecture
supports, for example, memory hotplug but not CPU hotplug, then the
/sys/devices/system/memory/crash_hotplug attribute file is present, but
the /sys/devices/system/cpu/crash_hotplug attribute file will NOT be
present.  Thus the udev rule skips userspace processing of memory hot
un/plug events, but the udev rule will evaluate false for CPU events, thus
allowing userspace to process CPU hot un/plug events (ie the
unload-then-reload of the kdump capture kernel).

Link: https://lkml.kernel.org/r/20230814214446.6659-5-eric.devolder@oracle.com
Signed-off-by: Eric DeVolder 
Reviewed-by: Sourabh Jain 
Acked-by: Hari Bathini 
Acked-by: Baoquan He 
Cc: Akhil Raj 
Cc: Bjorn Helgaas 
Cc: Borislav Petkov (AMD) 
Cc: Boris Ostrovsky 
Cc: Dave Hansen 
Cc: Dave Young 
Cc: David Hildenbrand 
Cc: Eric W. Biederman 
Cc: Greg Kroah-Hartman 
Cc: "H. Peter Anvin" 
Cc: Ingo Molnar 
Cc: Jonathan Corbet 
Cc: Konrad Rzeszutek Wilk 
Cc: Mimi Zohar 
Cc: Naveen N. Rao 
Cc: Oscar Salvador 
Cc: "Rafael J. Wysocki" 
Cc: Sean Christopherson 
Cc: Takashi Iwai 
Cc: Thomas Gleixner 
Cc: Thomas Weißschuh 
Cc: Valentin Schneider 
Cc: Vivek Goyal 
Cc: Vlastimil Babka 
Signed-off-by: Andrew Morton

Documentation: sysfs/memory: clarify some memory block device properties

2021-02-26T17:41:00+00:00

In commit 53cdc1cb29e8 ("drivers/base/memory.c: indicate all memory blocks
as removable") we changed the output of the "removable" property of memory
devices to return "1" if and only if the kernel supports memory offlining.

Let's update documentation, stating that the interface is legacy.  Also
update documentation of the "state" property and "valid_zones" properties.

Link: https://lkml.kernel.org/r/20210201181347.13262-3-david@redhat.com
Signed-off-by: David Hildenbrand 
Acked-by: Michal Hocko 
Reviewed-by: Oscar Salvador 
Cc: Dave Hansen 
Cc: Jonathan Corbet 
Cc: David Hildenbrand 
Cc: Greg Kroah-Hartman 
Cc: Jonathan Cameron 
Cc: Ilya Dryomov 
Cc: Mauro Carvalho Chehab 
Cc: Geert Uytterhoeven 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

drivers/base/memory: don't store phys_device in memory blocks

2021-02-26T17:41:00+00:00

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

Link: https://lkml.kernel.org/r/20210201181347.13262-2-david@redhat.com
Signed-off-by: David Hildenbrand 
Acked-by: Michal Hocko 
Reviewed-by: Oscar Salvador 
Cc: Dave Hansen 
Cc: Greg Kroah-Hartman 
Cc: Gerald Schaefer 
Cc: Jonathan Corbet 
Cc: "Rafael J. Wysocki" 
Cc: Mauro Carvalho Chehab 
Cc: Ilya Dryomov 
Cc: Vaibhav Jain 
Cc: Tom Rix 
Cc: Geert Uytterhoeven 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

docs: ABI: Drop trailing whitespace

2020-11-13T22:03:49+00:00

Remove all trailing whitespace from the ABI documentation.
Most of it was introduced during recent updates.

Signed-off-by: Geert Uytterhoeven 
Link: https://lore.kernel.org/r/20201110144033.3278499-1-geert+renesas@glider.be
Signed-off-by: Jonathan Corbet

docs: ABI: cleanup several ABI documents

2020-10-30T12:14:29+00:00

There are some ABI documents that, while they don't generate
any warnings, they have issues when parsed by get_abi.pl script
on its output result.

Address them, in order to provide a clean output.

Reviewed-by: Tom Rix  # for fpga-manager
Reviewed-By: Kajol Jain # for sysfs-bus-event_source-devices-hv_gpci and sysfs-bus-event_source-devices-hv_24x7
Acked-by: Jonathan Cameron  #for IIO
Acked-by: Oded Gabbay  # for Habanalabs
Acked-by: Vaibhav Jain  # for sysfs-bus-papr-pmem
Acked-by: Cezary Rojewski  # for catpt
Acked-by: Suzuki K Poulose 
Acked-by: Ilya Dryomov  # for rbd
Acked-by: Jonathan Corbet 
Signed-off-by: Mauro Carvalho Chehab 
Link: https://lore.kernel.org/r/5bc78e5b68ed1e9e39135173857cb2e753be868f.1604042072.git.mchehab+huawei@kernel.org
Signed-off-by: Greg Kroah-Hartman

memory-hotplug: add sysfs valid_zones attribute

2014-10-10T02:25:52+00:00

Currently memory-hotplug has two limits:

1. If the memory block is in ZONE_NORMAL, you can change it to
   ZONE_MOVABLE, but this memory block must be adjacent to ZONE_MOVABLE.

2. If the memory block is in ZONE_MOVABLE, you can change it to
   ZONE_NORMAL, but this memory block must be adjacent to ZONE_NORMAL.

With this patch, we can easy to know a memory block can be onlined to
which zone, and don't need to know the above two limits.

Updated the related Documentation.

[akpm@linux-foundation.org: use conventional comment layout]
[akpm@linux-foundation.org: fix build with CONFIG_MEMORY_HOTREMOVE=n]
[akpm@linux-foundation.org: remove unused local zone_prev]
Signed-off-by: Zhang Zhen 
Cc: Dave Hansen 
Cc: David Rientjes 
Cc: Toshi Kani 
Cc: Yasuaki Ishimatsu 
Cc: Naoya Horiguchi 
Cc: Wang Nan 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

Documentation: update broken web addresses.

2010-08-04T13:21:40+00:00

Below you will find an updated version from the original series bunching all patches into one big patch
updating broken web addresses that are located in Documentation/*
Some of the addresses date as far far back as 1995 etc... so searching became a bit difficult,
the best way to deal with these is to use web.archive.org to locate these addresses that are outdated.
Now there are also some addresses pointing to .spec files some are located, but some(after searching
on the companies site)where still no where to be found. In this case I just changed the address
to the company site this way the users can contact the company and they can locate them for the users.

Signed-off-by: Justin P. Mattock 
Signed-off-by: Thomas Weber 
Signed-off-by: Mike Frysinger 
Cc: Paulo Marques 
Cc: Randy Dunlap 
Cc: Michael Neuling 
Signed-off-by: Jiri Kosina

Documentation/: it's -> its where appropriate

2010-04-23T00:09:52+00:00

Fix obvious cases of "it's" being used when "its" was meant.

Signed-off-by: Francis Galiegue 
Acked-by: Randy Dunlap 
Signed-off-by: Jiri Kosina

mm: add numa node symlink for memory section in sysfs

2009-12-15T16:53:17+00:00

Commit c04fc586c (mm: show node to memory section relationship with
symlinks in sysfs) created symlinks from nodes to memory sections, e.g.

/sys/devices/system/node/node1/memory135 -> ../../memory/memory135

If you're examining the memory section though and are wondering what node
it might belong to, you can find it by grovelling around in sysfs, but
it's a little cumbersome.

Add a reverse symlink for each memory section that points back to the
node to which it belongs.

Signed-off-by: Alex Chiang 
Cc: Gary Hade 
Cc: Badari Pulavarty 
Cc: Ingo Molnar 
Acked-by: David Rientjes 
Cc: Greg KH 
Cc: Randy Dunlap 
Cc: David Rientjes 
Cc: KOSAKI Motohiro 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds