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Message-ID: <9acc6148-72eb-7016-dba9-46fa87ded5a5@redhat.com>
Date: Wed, 23 Sep 2020 10:04:35 +0200
From: David Hildenbrand <david@...hat.com>
To: Joao Martins <joao.m.martins@...cle.com>,
Dan Williams <dan.j.williams@...el.com>
Cc: akpm@...ux-foundation.org, Vishal Verma <vishal.l.verma@...el.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Pavel Tatashin <pasha.tatashin@...een.com>,
peterz@...radead.org, ard.biesheuvel@...aro.org,
linux-mm@...ck.org, linux-nvdimm@...ts.01.org,
linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v4 11/23] device-dax: Kill dax_kmem_res
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);
--
Thanks,
David / dhildenb
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