| Message ID | 20210608133855.20397-2-david@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | memory-hotplug.rst: complete admin-guide overhaul | expand |
On Tue 08-06-21 15:38:54, David Hildenbrand wrote: > We have the same content at Documentation/core-api/memory-hotplug.rst > and it doesn't fit into the admin-guide. The documentation was > accidentially duplicated when merging. > > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Oscar Salvador <osalvador@suse.de> > Cc: Michal Hocko <mhocko@suse.com> > Cc: Mike Kravetz <mike.kravetz@oracle.com> > Cc: Mike Rapoport <rppt@kernel.org> > Cc: Dave Hansen <dave.hansen@linux.intel.com> > Cc: Matthew Wilcox <willy@infradead.org> > Cc: Anshuman Khandual <anshuman.khandual@arm.com> > Cc: Muchun Song <songmuchun@bytedance.com> > Cc: Pavel Tatashin <pasha.tatashin@soleen.com> > Cc: Jonathan Corbet <corbet@lwn.net> > Cc: Stephen Rothwell <sfr@canb.auug.org.au> > Cc: linux-doc@vger.kernel.org > Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Michal Hocko <mhocko@suse.com> Thanks! > --- > .../admin-guide/mm/memory-hotplug.rst | 39 ------------------- > 1 file changed, 39 deletions(-) > > diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst > index c6bae2d77160..a783cf7c8e4c 100644 > --- a/Documentation/admin-guide/mm/memory-hotplug.rst > +++ b/Documentation/admin-guide/mm/memory-hotplug.rst > @@ -415,45 +415,6 @@ Need more implementation yet.... > - Guard from remove if not yet. > > > -Locking Internals > -================= > - > -When adding/removing memory that uses memory block devices (i.e. ordinary RAM), > -the device_hotplug_lock should be held to: > - > -- synchronize against online/offline requests (e.g. via sysfs). This way, memory > - block devices can only be accessed (.online/.state attributes) by user > - space once memory has been fully added. And when removing memory, we > - know nobody is in critical sections. > -- synchronize against CPU hotplug and similar (e.g. relevant for ACPI and PPC) > - > -Especially, there is a possible lock inversion that is avoided using > -device_hotplug_lock when adding memory and user space tries to online that > -memory faster than expected: > - > -- device_online() will first take the device_lock(), followed by > - mem_hotplug_lock > -- add_memory_resource() will first take the mem_hotplug_lock, followed by > - the device_lock() (while creating the devices, during bus_add_device()). > - > -As the device is visible to user space before taking the device_lock(), this > -can result in a lock inversion. > - > -onlining/offlining of memory should be done via device_online()/ > -device_offline() - to make sure it is properly synchronized to actions > -via sysfs. Holding device_hotplug_lock is advised (to e.g. protect online_type) > - > -When adding/removing/onlining/offlining memory or adding/removing > -heterogeneous/device memory, we should always hold the mem_hotplug_lock in > -write mode to serialise memory hotplug (e.g. access to global/zone > -variables). > - > -In addition, mem_hotplug_lock (in contrast to device_hotplug_lock) in read > -mode allows for a quite efficient get_online_mems/put_online_mems > -implementation, so code accessing memory can protect from that memory > -vanishing. > - > - > Future Work > =========== > > -- > 2.31.1
On Tue, Jun 08, 2021 at 03:38:54PM +0200, David Hildenbrand wrote: > We have the same content at Documentation/core-api/memory-hotplug.rst > and it doesn't fit into the admin-guide. The documentation was > accidentially duplicated when merging. > > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Oscar Salvador <osalvador@suse.de> > Cc: Michal Hocko <mhocko@suse.com> > Cc: Mike Kravetz <mike.kravetz@oracle.com> > Cc: Mike Rapoport <rppt@kernel.org> > Cc: Dave Hansen <dave.hansen@linux.intel.com> > Cc: Matthew Wilcox <willy@infradead.org> > Cc: Anshuman Khandual <anshuman.khandual@arm.com> > Cc: Muchun Song <songmuchun@bytedance.com> > Cc: Pavel Tatashin <pasha.tatashin@soleen.com> > Cc: Jonathan Corbet <corbet@lwn.net> > Cc: Stephen Rothwell <sfr@canb.auug.org.au> > Cc: linux-doc@vger.kernel.org > Signed-off-by: David Hildenbrand <david@redhat.com> Acked-by: Mike Rapoport <rppt@linux.ibm.com> > --- > .../admin-guide/mm/memory-hotplug.rst | 39 ------------------- > 1 file changed, 39 deletions(-) > > diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst > index c6bae2d77160..a783cf7c8e4c 100644 > --- a/Documentation/admin-guide/mm/memory-hotplug.rst > +++ b/Documentation/admin-guide/mm/memory-hotplug.rst > @@ -415,45 +415,6 @@ Need more implementation yet.... > - Guard from remove if not yet. > > > -Locking Internals > -================= > - > -When adding/removing memory that uses memory block devices (i.e. ordinary RAM), > -the device_hotplug_lock should be held to: > - > -- synchronize against online/offline requests (e.g. via sysfs). This way, memory > - block devices can only be accessed (.online/.state attributes) by user > - space once memory has been fully added. And when removing memory, we > - know nobody is in critical sections. > -- synchronize against CPU hotplug and similar (e.g. relevant for ACPI and PPC) > - > -Especially, there is a possible lock inversion that is avoided using > -device_hotplug_lock when adding memory and user space tries to online that > -memory faster than expected: > - > -- device_online() will first take the device_lock(), followed by > - mem_hotplug_lock > -- add_memory_resource() will first take the mem_hotplug_lock, followed by > - the device_lock() (while creating the devices, during bus_add_device()). > - > -As the device is visible to user space before taking the device_lock(), this > -can result in a lock inversion. > - > -onlining/offlining of memory should be done via device_online()/ > -device_offline() - to make sure it is properly synchronized to actions > -via sysfs. Holding device_hotplug_lock is advised (to e.g. protect online_type) > - > -When adding/removing/onlining/offlining memory or adding/removing > -heterogeneous/device memory, we should always hold the mem_hotplug_lock in > -write mode to serialise memory hotplug (e.g. access to global/zone > -variables). > - > -In addition, mem_hotplug_lock (in contrast to device_hotplug_lock) in read > -mode allows for a quite efficient get_online_mems/put_online_mems > -implementation, so code accessing memory can protect from that memory > -vanishing. > - > - > Future Work > =========== > > -- > 2.31.1 >
On Tue, Jun 08, 2021 at 03:38:54PM +0200, David Hildenbrand wrote: > We have the same content at Documentation/core-api/memory-hotplug.rst > and it doesn't fit into the admin-guide. The documentation was > accidentially duplicated when merging. > > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Oscar Salvador <osalvador@suse.de> > Cc: Michal Hocko <mhocko@suse.com> > Cc: Mike Kravetz <mike.kravetz@oracle.com> > Cc: Mike Rapoport <rppt@kernel.org> > Cc: Dave Hansen <dave.hansen@linux.intel.com> > Cc: Matthew Wilcox <willy@infradead.org> > Cc: Anshuman Khandual <anshuman.khandual@arm.com> > Cc: Muchun Song <songmuchun@bytedance.com> > Cc: Pavel Tatashin <pasha.tatashin@soleen.com> > Cc: Jonathan Corbet <corbet@lwn.net> > Cc: Stephen Rothwell <sfr@canb.auug.org.au> > Cc: linux-doc@vger.kernel.org > Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Oscar Salvador <osalvador@suse.de>
diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst index c6bae2d77160..a783cf7c8e4c 100644 --- a/Documentation/admin-guide/mm/memory-hotplug.rst +++ b/Documentation/admin-guide/mm/memory-hotplug.rst @@ -415,45 +415,6 @@ Need more implementation yet.... - Guard from remove if not yet. -Locking Internals -================= - -When adding/removing memory that uses memory block devices (i.e. ordinary RAM), -the device_hotplug_lock should be held to: - -- synchronize against online/offline requests (e.g. via sysfs). This way, memory - block devices can only be accessed (.online/.state attributes) by user - space once memory has been fully added. And when removing memory, we - know nobody is in critical sections. -- synchronize against CPU hotplug and similar (e.g. relevant for ACPI and PPC) - -Especially, there is a possible lock inversion that is avoided using -device_hotplug_lock when adding memory and user space tries to online that -memory faster than expected: - -- device_online() will first take the device_lock(), followed by - mem_hotplug_lock -- add_memory_resource() will first take the mem_hotplug_lock, followed by - the device_lock() (while creating the devices, during bus_add_device()). - -As the device is visible to user space before taking the device_lock(), this -can result in a lock inversion. - -onlining/offlining of memory should be done via device_online()/ -device_offline() - to make sure it is properly synchronized to actions -via sysfs. Holding device_hotplug_lock is advised (to e.g. protect online_type) - -When adding/removing/onlining/offlining memory or adding/removing -heterogeneous/device memory, we should always hold the mem_hotplug_lock in -write mode to serialise memory hotplug (e.g. access to global/zone -variables). - -In addition, mem_hotplug_lock (in contrast to device_hotplug_lock) in read -mode allows for a quite efficient get_online_mems/put_online_mems -implementation, so code accessing memory can protect from that memory -vanishing. - - Future Work ===========
We have the same content at Documentation/core-api/memory-hotplug.rst and it doesn't fit into the admin-guide. The documentation was accidentially duplicated when merging. Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Oscar Salvador <osalvador@suse.de> Cc: Michal Hocko <mhocko@suse.com> Cc: Mike Kravetz <mike.kravetz@oracle.com> Cc: Mike Rapoport <rppt@kernel.org> Cc: Dave Hansen <dave.hansen@linux.intel.com> Cc: Matthew Wilcox <willy@infradead.org> Cc: Anshuman Khandual <anshuman.khandual@arm.com> Cc: Muchun Song <songmuchun@bytedance.com> Cc: Pavel Tatashin <pasha.tatashin@soleen.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Stephen Rothwell <sfr@canb.auug.org.au> Cc: linux-doc@vger.kernel.org Signed-off-by: David Hildenbrand <david@redhat.com> --- .../admin-guide/mm/memory-hotplug.rst | 39 ------------------- 1 file changed, 39 deletions(-)