lkml.org 
[lkml]   [2020]   [Sep]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH v4 11/23] device-dax: Kill dax_kmem_res
From
Date
On 23.09.20 23:41, Dan Williams wrote:
> On Wed, Sep 23, 2020 at 1:04 AM David Hildenbrand <david@redhat.com> wrote:
>>
>> On 08.09.20 17:33, Joao Martins wrote:
>>> [Sorry for the late response]
>>>
>>> On 8/21/20 11:06 AM, David Hildenbrand wrote:
>>>> On 03.08.20 07:03, Dan Williams wrote:
>>>>> @@ -37,109 +45,94 @@ int dev_dax_kmem_probe(struct device *dev)
>>>>> * could be mixed in a node with faster memory, causing
>>>>> * unavoidable performance issues.
>>>>> */
>>>>> - numa_node = dev_dax->target_node;
>>>>> if (numa_node < 0) {
>>>>> dev_warn(dev, "rejecting DAX region with invalid node: %d\n",
>>>>> numa_node);
>>>>> return -EINVAL;
>>>>> }
>>>>>
>>>>> - /* Hotplug starting at the beginning of the next block: */
>>>>> - kmem_start = ALIGN(range->start, memory_block_size_bytes());
>>>>> -
>>>>> - kmem_size = range_len(range);
>>>>> - /* Adjust the size down to compensate for moving up kmem_start: */
>>>>> - kmem_size -= kmem_start - range->start;
>>>>> - /* Align the size down to cover only complete blocks: */
>>>>> - kmem_size &= ~(memory_block_size_bytes() - 1);
>>>>> - kmem_end = kmem_start + kmem_size;
>>>>> -
>>>>> - new_res_name = kstrdup(dev_name(dev), GFP_KERNEL);
>>>>> - if (!new_res_name)
>>>>> + res_name = kstrdup(dev_name(dev), GFP_KERNEL);
>>>>> + if (!res_name)
>>>>> return -ENOMEM;
>>>>>
>>>>> - /* Region is permanently reserved if hotremove fails. */
>>>>> - new_res = request_mem_region(kmem_start, kmem_size, new_res_name);
>>>>> - if (!new_res) {
>>>>> - dev_warn(dev, "could not reserve region [%pa-%pa]\n",
>>>>> - &kmem_start, &kmem_end);
>>>>> - kfree(new_res_name);
>>>>> + res = request_mem_region(range.start, range_len(&range), res_name);
>>>>
>>>> I think our range could be empty after aligning. I assume
>>>> request_mem_region() would check that, but maybe we could report a
>>>> better error/warning in that case.
>>>>
>>> dax_kmem_range() already returns a memory-block-aligned @range but
>>> IIUC request_mem_region() isn't checking for that. Having said that
>>> the returned @res wouldn't be different from the passed range.start.
>>>
>>>>> /*
>>>>> * Ensure that future kexec'd kernels will not treat this as RAM
>>>>> * automatically.
>>>>> */
>>>>> - rc = add_memory_driver_managed(numa_node, new_res->start,
>>>>> - resource_size(new_res), kmem_name);
>>>>> + rc = add_memory_driver_managed(numa_node, res->start,
>>>>> + resource_size(res), kmem_name);
>>>>> +
>>>>> + res->flags |= IORESOURCE_BUSY;
>>>>
>>>> Hm, I don't think that's correct. Any specific reason why to mark the
>>>> not-added, unaligned parts BUSY? E.g., walk_system_ram_range() could
>>>> suddenly stumble over it - and e.g., similarly kexec code when trying to
>>>> find memory for placing kexec images. I think we should leave this
>>>> !BUSY, just as it is right now.
>>>>
>>> Agreed.
>>>
>>>>> if (rc) {
>>>>> - release_resource(new_res);
>>>>> - kfree(new_res);
>>>>> - kfree(new_res_name);
>>>>> + release_mem_region(range.start, range_len(&range));
>>>>> + kfree(res_name);
>>>>> return rc;
>>>>> }
>>>>> - dev_dax->dax_kmem_res = new_res;
>>>>> +
>>>>> + dev_set_drvdata(dev, res_name);
>>>>>
>>>>> return 0;
>>>>> }
>>>>>
>>>>> #ifdef CONFIG_MEMORY_HOTREMOVE
>>>>> -static int dev_dax_kmem_remove(struct device *dev)
>>>>> +static void dax_kmem_release(struct dev_dax *dev_dax)
>>>>> {
>>>>> - struct dev_dax *dev_dax = to_dev_dax(dev);
>>>>> - struct resource *res = dev_dax->dax_kmem_res;
>>>>> - resource_size_t kmem_start = res->start;
>>>>> - resource_size_t kmem_size = resource_size(res);
>>>>> - const char *res_name = res->name;
>>>>> int rc;
>>>>> + struct device *dev = &dev_dax->dev;
>>>>> + const char *res_name = dev_get_drvdata(dev);
>>>>> + struct range range = dax_kmem_range(dev_dax);
>>>>>
>>>>> /*
>>>>> * We have one shot for removing memory, if some memory blocks were not
>>>>> * offline prior to calling this function remove_memory() will fail, and
>>>>> * there is no way to hotremove this memory until reboot because device
>>>>> - * unbind will succeed even if we return failure.
>>>>> + * unbind will proceed regardless of the remove_memory result.
>>>>> */
>>>>> - rc = remove_memory(dev_dax->target_node, kmem_start, kmem_size);
>>>>> - if (rc) {
>>>>> - any_hotremove_failed = true;
>>>>> - dev_err(dev,
>>>>> - "DAX region %pR cannot be hotremoved until the next reboot\n",
>>>>> - res);
>>>>> - return rc;
>>>>> + rc = remove_memory(dev_dax->target_node, range.start, range_len(&range));
>>>>> + if (rc == 0) {
>>>>
>>>> if (!rc) ?
>>>>
>>> Better off would be to keep the old order:
>>>
>>> if (rc) {
>>> any_hotremove_failed = true;
>>> dev_err(dev, "%#llx-%#llx cannot be hotremoved until the next reboot\n",
>>> range.start, range.end);
>>> return;
>>> }
>>>
>>> release_mem_region(range.start, range_len(&range));
>>> dev_set_drvdata(dev, NULL);
>>> kfree(res_name);
>>> return;
>>>
>>>
>>>>> + release_mem_region(range.start, range_len(&range));
>>>>
>>>> remove_memory() does a release_mem_region_adjustable(). Don't you
>>>> actually want to release the *unaligned* region you requested?
>>>>
>>> Isn't it what we're doing here?
>>> (The release_mem_region_adjustable() is using the same
>>> dax_kmem-aligned range and there's no split/adjust)
>>>
>>> Meaning right now (+ parent marked as !BUSY), and if I am understanding
>>> this correctly:
>>>
>>> request_mem_region(range.start, range_len)
>>> __request_region(iomem_res, range.start, range_len) -> alloc @parent
>>> add_memory_driver_managed(parent.start, resource_size(parent))
>>> __request_region(parent.start, resource_size(parent)) -> alloc @child
>>>
>>> [...]
>>>
>>> remove_memory(range.start, range_len)
>>> request_mem_region_adjustable(range.start, range_len)
>>> __release_region(range.start, range_len) -> remove @child
>>>
>>> release_mem_region(range.start, range_len)
>>> __release_region(range.start, range_len) -> doesn't remove @parent because !BUSY?
>>>
>>> The add/removal of this relies on !BUSY. But now I am wondering if the parent remaining
>>> unreleased is deliberate even on CONFIG_MEMORY_HOTREMOVE=y.
>>>
>>> Joao
>>>
>>
>> Thinking about it, if we don't set the parent resource BUSY (which is
>> what I think is the right way of doing things), and don't want to store
>> the parent resource pointer, we could add something like
>> lookup_resource() - e.g., lookup_mem_resource() - , however, searching
>> properly in the whole hierarchy (instead of only the first level), and
>> traversing down to the last hierarchy. Then it would be as simple as
>>
>> remove_memory(range.start, range_len)
>> res = lookup_mem_resource(range.start);
>> release_resource(res);
>
> Another thought... I notice that you've taught
> register_memory_resource() a IORESOURCE_MEM_DRIVER_MANAGED special
> case. Lets just make the assumption of add_memory_driver_managed()
> that it is the driver's responsibility to mark the range busy before
> calling, and the driver's responsibility to release the region. I.e.
> validate (rather than request) that the range is busy in
> register_memory_resource(), and teach release_memory_resource() to
> skip releasing the region when the memory is marked driver managed.
> That would let dax_kmem drop its manipulation of the 'busy' flag which
> is a layering violation no matter how many comments we put around it.

IIUC, that won't work for virtio-mem, whereby the parent resource spans
multiple possible (future) add_memory_driver_managed() calls and is
(just like for kmem) a pure indication to which device memory ranges belong.

For example, when exposing 2GB via a virtio-mem device with max 4GB:

(/proc/iomem)
240000000-33fffffff : virtio0
240000000-2bfffffff : System RAM (virtio_mem)

And after hotplugging additional 2GB:

240000000-33fffffff : virtio0
240000000-33fffffff : System RAM (virtio_mem)

So marking "virtio0" always BUSY (especially right from the start) would
be wrong. The assumption is that anything that's IORESOURCE_SYSTEM_RAM
and IORESOUCE_BUSY is currently added to the system as system RAM (e.g.,
after add_memory() and friends, or during boot).

I do agree that manually clearing the busy flag is ugly. What we most
probably want is request_mem_region() that performs similar checks (no
overlaps with existing BUSY resources), but doesn't set the region busy.

--
Thanks,

David / dhildenb

\
 
 \ /
  Last update: 2020-09-24 09:26    [W:0.164 / U:3.152 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site