linux-kernel - Re: [PATCH v2 4/5] mm: memory_hotplug: Add memory hotremove probe device

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Message-Id: <20171124104401.GD18120@samekh>
Date:   Fri, 24 Nov 2017 10:44:01 +0000
From:   Andrea Reale <ar@...ux.vnet.ibm.com>
To:     zhong jiang <zhongjiang@...wei.com>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, m.bielski@...tualopensystems.com,
        arunks@....qualcomm.com, mark.rutland@....com,
        scott.branden@...adcom.com, will.deacon@....com,
        qiuxishi@...wei.com, catalin.marinas@....com, mhocko@...e.com,
        realean2@...ibm.com
Subject: Re: [PATCH v2 4/5] mm: memory_hotplug: Add memory hotremove probe
 device

Hi zhongjiang,

On Fri 24 Nov 2017, 18:35, zhong jiang wrote:
> HI, Andrea
> 
> I don't see "memory_add_physaddr_to_nid" in arch/arm64.
> Am I miss something?

When !CONFIG_NUMA it is defined in include/linux/memory_hotplug.h as 0.
In patch 1/5 of this series we require !NUMA to enable
ARCH_ENABLE_MEMORY_HOTPLUG.

The reason for this simplification is simply that we would not know how
to decide the correct node to which to add memory when NUMA is on.
Any suggestion on that matter is welcome. 

Thanks,
Andrea

> Thnaks
> zhongjiang
> 
> On 2017/11/23 19:14, 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.
> >
> > Signed-off-by: Andrea Reale <ar@...ux.vnet.ibm.com>
> > Signed-off-by: Maciej Bielski <m.bielski@...tualopensystems.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);
> > +	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
> 
>