On Fri, Oct 01, 2021 at 10:04:24AM +0200, David Hildenbrand wrote:
On 30.09.21 23:21, Mike Rapoport wrote:
On Wed, Sep 29, 2021 at 06:54:01PM +0200, David Hildenbrand wrote:
On 29.09.21 18:39, Mike Rapoport wrote:
Hi,
On Mon, Sep 27, 2021 at 05:05:17PM +0200, David Hildenbrand wrote:
Let's add a flag that corresponds to IORESOURCE_SYSRAM_DRIVER_MANAGED.
Similar to MEMBLOCK_HOTPLUG, most infrastructure has to treat such memory
like ordinary MEMBLOCK_NONE memory -- for example, when selecting memory
regions to add to the vmcore for dumping in the crashkernel via
for_each_mem_range().
Can you please elaborate on the difference in semantics of MEMBLOCK_HOTPLUG
and MEMBLOCK_DRIVER_MANAGED?
Unless I'm missing something they both mark memory that can be unplugged
anytime and so it should not be used in certain cases. Why is there a need
for a new flag?
In the cover letter I have "Alternative B: Reuse MEMBLOCK_HOTPLUG.
MEMBLOCK_HOTPLUG serves a different purpose, though.", but looking into the
details it won't work as is.
MEMBLOCK_HOTPLUG is used to mark memory early during boot that can later get
hotunplugged again and should be placed into ZONE_MOVABLE if the
"movable_node" kernel parameter is set.
The confusing part is that we talk about "hotpluggable" but really mean
"hotunpluggable": the reason is that HW flags DIMM slots that can later be
hotplugged as "hotpluggable" even though there is already something
hotplugged.
MEMBLOCK_HOTPLUG name is indeed somewhat confusing, but still it's core
meaning "this memory may be removed" which does not differ from what
IORESOURCE_SYSRAM_DRIVER_MANAGED means.
MEMBLOCK_HOTPLUG regions are indeed placed into ZONE_MOVABLE, but more
importantly, they are avoided when we allocate memory from memblock.
So, in my view, both flags mean that the memory may be removed and it
should not be used for certain types of allocations.
The semantics are different:
MEMBLOCK_HOTPLUG: memory is indicated as "System RAM" in the
firmware-provided memory map and added to the system early during boot; we
want this memory to be managed by ZONE_MOVABLE with "movable_node" set on
the kernel command line, because only then we want it to be hotpluggable
again. kexec *has to* indicate this memory to the second kernel and can
place kexec-images on this memory. After memory hotunplug, kexec has to be
re-armed.
MEMBLOCK_DRIVER_MANAGED: memory is not indicated as System RAM" in the
firmware-provided memory map; this memory is always detected and added to
the system by a driver; memory might not actually be physically
hotunpluggable and the ZONE selection does not depend on "movable_core".
kexec *must not* indicate this memory to the second kernel and *must not*
place kexec-images on this memory.
Ok, this clarifies.
This explanation should be a part of the changelog. The sentences about the
zone selection could be probably skipped, because they are less important
for this case. E.g something like:
MEMBLOCK_HOTPLUG: memory is indicated as "System RAM" in the
firmware-provided memory map and added to the system early during boot;
kexec *has to* indicate this memory to the second kernel and can place
kexec-images on this memory. After memory hotunplug, kexec has to be
re-armed.
MEMBLOCK_DRIVER_MANAGED: memory is not indicated as "System RAM" in the
firmware-provided memory map; this memory is always detected and added to
the system by a driver; memory might not actually be physically
hotunpluggable. kexec *must not* indicate this memory to the second kernel
and *must not* place kexec-images on this memory.
--
Sincerely yours,
Mike.
