* [PATCH] docs: reorder memory-hotplug documentation
@ 2019-05-14 8:23 Mike Rapoport
2019-05-21 10:41 ` David Hildenbrand
0 siblings, 1 reply; 5+ messages in thread
From: Mike Rapoport @ 2019-05-14 8:23 UTC (permalink / raw)
To: Jonathan Corbet; +Cc: linux-doc, linux-mm, linux-kernel, Mike Rapoport
The "Locking Internals" section of the memory-hotplug documentation is
duplicated in admin-guide and core-api. Drop the admin-guide copy as
locking internals does not belong there.
While on it, move the "Future Work" section to the core-api part.
Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
---
Documentation/admin-guide/mm/memory-hotplug.rst | 51 -------------------------
Documentation/core-api/memory-hotplug.rst | 11 ++++++
2 files changed, 11 insertions(+), 51 deletions(-)
diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst
index 5c4432c..72090ba 100644
--- a/Documentation/admin-guide/mm/memory-hotplug.rst
+++ b/Documentation/admin-guide/mm/memory-hotplug.rst
@@ -391,54 +391,3 @@ Physical memory remove
Need more implementation yet....
- Notification completion of remove works by OS to firmware.
- 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
-===========
-
- - allowing memory hot-add to ZONE_MOVABLE. maybe we need some switch like
- sysctl or new control file.
- - showing memory block and physical device relationship.
- - test and make it better memory offlining.
- - support HugeTLB page migration and offlining.
- - memmap removing at memory offline.
- - physical remove memory.
diff --git a/Documentation/core-api/memory-hotplug.rst b/Documentation/core-api/memory-hotplug.rst
index de7467e..e08be1c 100644
--- a/Documentation/core-api/memory-hotplug.rst
+++ b/Documentation/core-api/memory-hotplug.rst
@@ -123,3 +123,14 @@ 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
+===========
+
+ - allowing memory hot-add to ZONE_MOVABLE. maybe we need some switch like
+ sysctl or new control file.
+ - showing memory block and physical device relationship.
+ - test and make it better memory offlining.
+ - support HugeTLB page migration and offlining.
+ - memmap removing at memory offline.
+ - physical remove memory.
--
2.7.4
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] docs: reorder memory-hotplug documentation
2019-05-14 8:23 [PATCH] docs: reorder memory-hotplug documentation Mike Rapoport
@ 2019-05-21 10:41 ` David Hildenbrand
2019-05-21 16:00 ` Mike Rapoport
2019-05-21 16:11 ` Oscar Salvador
0 siblings, 2 replies; 5+ messages in thread
From: David Hildenbrand @ 2019-05-21 10:41 UTC (permalink / raw)
To: Mike Rapoport, Jonathan Corbet; +Cc: linux-doc, linux-mm, linux-kernel
On 14.05.19 10:23, Mike Rapoport wrote:
> The "Locking Internals" section of the memory-hotplug documentation is
> duplicated in admin-guide and core-api. Drop the admin-guide copy as
> locking internals does not belong there.
>
> While on it, move the "Future Work" section to the core-api part.
Looks sane, but the future work part is really outdated, can we remove
this completely?
>
> Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> ---
> Documentation/admin-guide/mm/memory-hotplug.rst | 51 -------------------------
> Documentation/core-api/memory-hotplug.rst | 11 ++++++
> 2 files changed, 11 insertions(+), 51 deletions(-)
>
> diff --git a/Documentation/admin-guide/mm/memory-hotplug.rst b/Documentation/admin-guide/mm/memory-hotplug.rst
> index 5c4432c..72090ba 100644
> --- a/Documentation/admin-guide/mm/memory-hotplug.rst
> +++ b/Documentation/admin-guide/mm/memory-hotplug.rst
> @@ -391,54 +391,3 @@ Physical memory remove
> Need more implementation yet....
> - Notification completion of remove works by OS to firmware.
> - 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
> -===========
> -
> - - allowing memory hot-add to ZONE_MOVABLE. maybe we need some switch like
> - sysctl or new control file.
> - - showing memory block and physical device relationship.
> - - test and make it better memory offlining.
> - - support HugeTLB page migration and offlining.
> - - memmap removing at memory offline.
> - - physical remove memory.
> diff --git a/Documentation/core-api/memory-hotplug.rst b/Documentation/core-api/memory-hotplug.rst
> index de7467e..e08be1c 100644
> --- a/Documentation/core-api/memory-hotplug.rst
> +++ b/Documentation/core-api/memory-hotplug.rst
> @@ -123,3 +123,14 @@ 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
> +===========
> +
> + - allowing memory hot-add to ZONE_MOVABLE. maybe we need some switch like
> + sysctl or new control file.
... that already works if I am not completely missing the point here
> + - showing memory block and physical device relationship.
... that is available for s390x only AFAIK
> + - test and make it better memory offlining.
... no big news ;)
> + - support HugeTLB page migration and offlining.
... I remember that Oscar was doing something in that area, Oscar?
> + - memmap removing at memory offline.
... no, we don't want this. However, we should properly clean up zone
information when offlining
> + - physical remove memory.
... I don't even understand what that means.
I'd vote for removing the future work part, this is pretty outdated.
--
Thanks,
David / dhildenb
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] docs: reorder memory-hotplug documentation
2019-05-21 10:41 ` David Hildenbrand
@ 2019-05-21 16:00 ` Mike Rapoport
2019-05-21 16:11 ` Oscar Salvador
1 sibling, 0 replies; 5+ messages in thread
From: Mike Rapoport @ 2019-05-21 16:00 UTC (permalink / raw)
To: David Hildenbrand; +Cc: Jonathan Corbet, linux-doc, linux-mm, linux-kernel
On Tue, May 21, 2019 at 12:41:50PM +0200, David Hildenbrand wrote:
> On 14.05.19 10:23, Mike Rapoport wrote:
> > The "Locking Internals" section of the memory-hotplug documentation is
> > duplicated in admin-guide and core-api. Drop the admin-guide copy as
> > locking internals does not belong there.
> >
> > While on it, move the "Future Work" section to the core-api part.
>
> Looks sane, but the future work part is really outdated, can we remove
> this completely?
>
> >
> > Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
> > ---
> > +
> > +Future Work
> > +===========
> > +
> > + - allowing memory hot-add to ZONE_MOVABLE. maybe we need some switch like
> > + sysctl or new control file.
>
> ... that already works if I am not completely missing the point here
>
> > + - showing memory block and physical device relationship.
>
> ... that is available for s390x only AFAIK
>
> > + - test and make it better memory offlining.
>
> ... no big news ;)
>
> > + - support HugeTLB page migration and offlining.
>
> ... I remember that Oscar was doing something in that area, Oscar?
>
> > + - memmap removing at memory offline.
>
> ... no, we don't want this. However, we should properly clean up zone
> information when offlining
>
> > + - physical remove memory.
>
> ... I don't even understand what that means.
>
>
> I'd vote for removing the future work part, this is pretty outdated.
Frankly, I haven't looked at the details, just simply moved the text over.
I don't mind sending another mechanical patch that removes the future work
part.
But it would be far better if somebody who's actively working on memory
hotplug would replace it with a description how this actually works ;-)
> --
>
> Thanks,
>
> David / dhildenb
>
--
Sincerely yours,
Mike.
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] docs: reorder memory-hotplug documentation
2019-05-21 10:41 ` David Hildenbrand
2019-05-21 16:00 ` Mike Rapoport
@ 2019-05-21 16:11 ` Oscar Salvador
2019-05-22 7:29 ` David Hildenbrand
1 sibling, 1 reply; 5+ messages in thread
From: Oscar Salvador @ 2019-05-21 16:11 UTC (permalink / raw)
To: David Hildenbrand
Cc: Mike Rapoport, Jonathan Corbet, linux-doc, linux-mm, linux-kernel
On Tue, May 21, 2019 at 12:41:50PM +0200, David Hildenbrand wrote:
> > +Future Work
> > +===========
> > +
> > + - allowing memory hot-add to ZONE_MOVABLE. maybe we need some switch like
> > + sysctl or new control file.
>
> ... that already works if I am not completely missing the point here
It does.
> > + - support HugeTLB page migration and offlining.
>
> ... I remember that Oscar was doing something in that area, Oscar?
Yes, in general offlinining on hugetlb pages was already working, but we did not
allow to offline 1GB-hugetlb pages on x86_64.
I removed that limitation with
("commit: 10eeadf3045c mm,memory_hotplug: unlock 1GB-hugetlb on x86_64") , so now
offlining on hugetlb pages should be fully operative.
> I'd vote for removing the future work part, this is pretty outdated.
Instead of removing it, I would rather make it consistent with the present.
E.g:
- Move page handling from memory-hotremove to offline stage
- Enable a way to allocate vmemmap pages from hot-added memory
etc.
--
Oscar Salvador
SUSE L3
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] docs: reorder memory-hotplug documentation
2019-05-21 16:11 ` Oscar Salvador
@ 2019-05-22 7:29 ` David Hildenbrand
0 siblings, 0 replies; 5+ messages in thread
From: David Hildenbrand @ 2019-05-22 7:29 UTC (permalink / raw)
To: Oscar Salvador
Cc: Mike Rapoport, Jonathan Corbet, linux-doc, linux-mm, linux-kernel
On 21.05.19 18:11, Oscar Salvador wrote:
> On Tue, May 21, 2019 at 12:41:50PM +0200, David Hildenbrand wrote:
>>> +Future Work
>>> +===========
>>> +
>>> + - allowing memory hot-add to ZONE_MOVABLE. maybe we need some switch like
>>> + sysctl or new control file.
>>
>> ... that already works if I am not completely missing the point here
>
> It does.
>
>>> + - support HugeTLB page migration and offlining.
>>
>> ... I remember that Oscar was doing something in that area, Oscar?
>
> Yes, in general offlinining on hugetlb pages was already working, but we did not
> allow to offline 1GB-hugetlb pages on x86_64.
> I removed that limitation with
> ("commit: 10eeadf3045c mm,memory_hotplug: unlock 1GB-hugetlb on x86_64") , so now
> offlining on hugetlb pages should be fully operative.
>
>> I'd vote for removing the future work part, this is pretty outdated.
>
> Instead of removing it, I would rather make it consistent with the present.
> E.g:
>
> - Move page handling from memory-hotremove to offline stage
> - Enable a way to allocate vmemmap pages from hot-added memory
> etc.
>
>
Fair enough, but at least the current content is absolutely useless and
confusing/misleading.
--
Thanks,
David / dhildenb
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2019-05-22 7:29 UTC | newest]
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2019-05-14 8:23 [PATCH] docs: reorder memory-hotplug documentation Mike Rapoport
2019-05-21 10:41 ` David Hildenbrand
2019-05-21 16:00 ` Mike Rapoport
2019-05-21 16:11 ` Oscar Salvador
2019-05-22 7:29 ` David Hildenbrand
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