Re: Cannot hot remove a memory device

From: Yasuaki Ishimatsu
Date: Mon Aug 05 2013 - 04:00:41 EST


(2013/08/05 13:00), Yasuaki Ishimatsu wrote:
(2013/08/04 9:37), Toshi Kani wrote:
On Sat, 2013-08-03 at 03:01 +0200, Rafael J. Wysocki wrote:
On Friday, August 02, 2013 06:04:40 PM Toshi Kani wrote:
On Sat, 2013-08-03 at 01:43 +0200, Rafael J. Wysocki wrote:
On Friday, August 02, 2013 03:46:15 PM Toshi Kani wrote:
On Thu, 2013-08-01 at 23:43 +0200, Rafael J. Wysocki wrote:
Hi,

Thanks for your report.

On Thursday, August 01, 2013 05:37:21 PM Yasuaki Ishimatsu wrote:
By following commit, I cannot hot remove a memory device.

ACPI / memhotplug: Bind removable memory blocks to ACPI device nodes
commit e2ff39400d81233374e780b133496a2296643d7d

Details are follows:
When I add a memory device, acpi_memory_enable_device() always fails
as follows:

...
[ 1271.114116] [ffffea121c400000-ffffea121c7fffff] PMD -> [ffff880813c00000-ffff880813ffffff] on node 3
[ 1271.128682] [ffffea121c800000-ffffea121cbfffff] PMD -> [ffff880813800000-ffff880813bfffff] on node 3
[ 1271.143298] [ffffea121cc00000-ffffea121cffffff] PMD -> [ffff880813000000-ffff8808133fffff] on node 3
[ 1271.157799] [ffffea121d000000-ffffea121d3fffff] PMD -> [ffff880812c00000-ffff880812ffffff] on node 3
[ 1271.172341] [ffffea121d400000-ffffea121d7fffff] PMD -> [ffff880812800000-ffff880812bfffff] on node 3
[ 1271.186872] [ffffea121d800000-ffffea121dbfffff] PMD -> [ffff880812400000-ffff8808127fffff] on node 3
[ 1271.201481] [ffffea121dc00000-ffffea121dffffff] PMD -> [ffff880812000000-ffff8808123fffff] on node 3
[ 1271.216041] [ffffea121e000000-ffffea121e3fffff] PMD -> [ffff880811c00000-ffff880811ffffff] on node 3
[ 1271.230623] [ffffea121e400000-ffffea121e7fffff] PMD -> [ffff880811800000-ffff880811bfffff] on node 3
[ 1271.245148] [ffffea121e800000-ffffea121ebfffff] PMD -> [ffff880811400000-ffff8808117fffff] on node 3
[ 1271.259683] [ffffea121ec00000-ffffea121effffff] PMD -> [ffff880811000000-ffff8808113fffff] on node 3
[ 1271.274194] [ffffea121f000000-ffffea121f3fffff] PMD -> [ffff880810c00000-ffff880810ffffff] on node 3
[ 1271.288764] [ffffea121f400000-ffffea121f7fffff] PMD -> [ffff880810800000-ffff880810bfffff] on node 3

It appears that each memory object only has 64MB of memory. This is
less than the memory block size, which is 128MB. This means that a
single memory block associates with two ACPI memory device objects.

That'd be bad.

How did that work before if that indeed is the case?

Well, it looks to me that it has never worked before...

...
[ 1271.325841] acpi PNP0C80:03: acpi_memory_enable_device() error

Well, the only new way acpi_memory_enable_device() can fail after that commit
is a failure in acpi_bind_memory_blocks().

Agreed.

This means that either handle is NULL, which I think we can exclude, because
acpi_memory_enable_device() wouldn't be called at all if that were the case, or
there's a more subtle error in acpi_bind_one().

One that comes to mind is that we may be calling acpi_bind_one() twice for the
same memory region, in which it will trigger -EINVAL from the sanity check in
there.

I think it fails with -EINVAL at the place with dev_warn(dev, "ACPI
handle is already set\n"). When two ACPI memory objects associate with
a same memory block, the bind procedure of the 2nd ACPI memory object
sees that ACPI_HANDLE(dev) is already set to the 1st ACPI memory object.

That sound's plausible, but I wonder how we can fix that?

There's no way for a single physical device to have two different ACPI
"companions". It looks like the memory blocks should be 64 M each in that
case. Or we need to create two child devices for each memory block and
associate each of them with an ACPI object. That would lead to complications
in the user space interface, though.

Right. Even bigger issue is that I do not think __add_pages() and
__remove_pages() can add / delete a memory chunk that is less than
128MB. 128MB is the granularity of them. So, we may just have to fail
this case gracefully.

Sigh.

BTW, why do you think they are 64 M each (it's late and I'm obviously tired)?

Oops! Sorry, I had confused the above messages with the one in
init_memory_mapping(), which shows a memory range being added, i.e. the
size of an ACPI memory device object. But the above messages actually
came from vmemmap_populate_hugepages(), which was called during boot-up.
So, these messages have nothing to do with ACPI memory device objects.
And even worse, I do not seem to be able to count a number of zeros...
In the above messages, each memory range is 4MB (0x400000), not 64MB
(0x4000000)... My bad. :-(

So, while we may still need to do something for the less-than-128MB
issue, Yasuaki may be hitting a different one. Let's wait for Yasuaki
to give us more info.

acpi_bind_memory_blocks() failed with -ENOSPC.

int acpi_bind_one(struct device *dev, acpi_handle handle)
{
...
/* allocate physical node id according to physical_node_id_bitmap */
physical_node->node_id =
find_first_zero_bit(acpi_dev->physical_node_id_bitmap,
ACPI_MAX_PHYSICAL_NODE);
if (physical_node->node_id >= ACPI_MAX_PHYSICAL_NODE) {
retval = -ENOSPC; => here
goto err_free;
}

When adding memory device, acpi_bind_memroy_blocks() calls acpi_bind_one()
"memory device size / 128MiB" times. So ACPI_MAX_PHYSICAL_NODE need to
be set "memory device size / 128MiB" or more. But ACPI_MAX_PHYSICAL_NODE is 32.
So acpi_bind_memory_blocks() always failed with -ENOSPC.


I'll test again after increasing ACPI_MAX_PHYSICAL_NODE to enough size.

Additional info:
When I increased ACPI_MAX_PHYSICAL_NODE to 1024 and change size of
acpi_device_physical_node->node_it into u32, I could hot remove memory
device. But even if ACPI_MAX_PHYSICAL_NODE is set to 1024, same problem
will occurs since it just supports 124GiB memory. So we need a way to change
ACPI_MAX_PHYSICAL_NODE dynamically.

Thanks,
Yasuaki Ishimatsu


Thanks,
Yasuaki Ishimatsu


Thanks,
-Toshi












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