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SubjectRe: [PATCH v2 4/5] mm: memory_hotplug: Add memory hotremove probe device
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On 23/11/17 11:14, Andrea Reale wrote:
> Adding a "remove" sysfs handle that can be used to trigger
> memory hotremove manually, exactly simmetrically with
> what happens with the "probe" device for hot-add.
>
> This is usueful for architecture that do not rely on
> ACPI for memory hot-remove.

Is there a real-world use-case for this, or is it mostly just a handy
development feature?

> Signed-off-by: Andrea Reale <ar@linux.vnet.ibm.com>
> Signed-off-by: Maciej Bielski <m.bielski@virtualopensystems.com>
> ---
> drivers/base/memory.c | 34 +++++++++++++++++++++++++++++++++-
> 1 file changed, 33 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> index 1d60b58..8ccb67c 100644
> --- a/drivers/base/memory.c
> +++ b/drivers/base/memory.c
> @@ -530,7 +530,36 @@ memory_probe_store(struct device *dev, struct device_attribute *attr,
> }
>
> static DEVICE_ATTR(probe, S_IWUSR, NULL, memory_probe_store);
> -#endif
> +
> +#ifdef CONFIG_MEMORY_HOTREMOVE
> +static ssize_t
> +memory_remove_store(struct device *dev,
> + struct device_attribute *attr, const char *buf, size_t count)
> +{
> + u64 phys_addr;
> + int nid, ret;
> + unsigned long pages_per_block = PAGES_PER_SECTION * sections_per_block;
> +
> + ret = kstrtoull(buf, 0, &phys_addr);
> + if (ret)
> + return ret;
> +
> + if (phys_addr & ((pages_per_block << PAGE_SHIFT) - 1))
> + return -EINVAL;
> +
> + nid = memory_add_physaddr_to_nid(phys_addr);

This call looks a bit odd, since you're not doing a memory add. In fact,
any memory being removed should already be fully known-about, so AFAICS
it should be simple to get everything you need to know (including
potentially the online status as mentioned earlier), through 'normal'
methods, e.g. page_to_nid() or similar.

Robin.

> + ret = lock_device_hotplug_sysfs();
> + if (ret)
> + return ret;
> +
> + remove_memory(nid, phys_addr,
> + MIN_MEMORY_BLOCK_SIZE * sections_per_block);
> + unlock_device_hotplug();
> + return count;
> +}
> +static DEVICE_ATTR(remove, S_IWUSR, NULL, memory_remove_store);
> +#endif /* CONFIG_MEMORY_HOTREMOVE */
> +#endif /* CONFIG_ARCH_MEMORY_PROBE */
>
> #ifdef CONFIG_MEMORY_FAILURE
> /*
> @@ -790,6 +819,9 @@ bool is_memblock_offlined(struct memory_block *mem)
> static struct attribute *memory_root_attrs[] = {
> #ifdef CONFIG_ARCH_MEMORY_PROBE
> &dev_attr_probe.attr,
> +#ifdef CONFIG_MEMORY_HOTREMOVE
> + &dev_attr_remove.attr,
> +#endif
> #endif
>
> #ifdef CONFIG_MEMORY_FAILURE
>

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