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From: Oscar Salvador <>
To: David Hildenbrand <>
Cc:,,,,,,,,,,, Oscar Salvador <>
Subject: Re: [RFC v2 2/2] mm/memory_hotplug: Shrink spanned pages when offlining memory
Date: Wed, 22 Aug 2018 09:50:20 +0200	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Tue, Aug 21, 2018 at 03:17:10PM +0200, David Hildenbrand wrote:
> > add_device_memory is in charge of
> I wouldn't use the terminology of onlining/offlining here. That applies
> rather to memory that is exposed to the rest of the system (e.g. buddy
> allocator, has underlying memory block devices). I guess it is rather a
> pure setup/teardown of that device memory.

Hi David,

I am not sure if you are referring to:

a) calling either arch_add_memory() or add_pages(), depending on whether
   we want a linear mapping
b) online the memory sections that correspond to the pfn range
c) calling move_pfn_range_to_zone() being zone ZONE_DEVICE to
   expand zone/pgdat spanned pages and initialize its pages

Well, that is partialy true.
I mean, in order to make this work, we need to offline/online the memory
sections, because shrink_pages will rely on that from now on.
Is what we do when online/offline pages, but since device memory
does not go through the "official" channels, we need to do it there
as well.

Sure I can use another terminology, but since that is what
offline/online_mem_sections do, I just came up with that.

> I would really like to see the mem_hotplug_begin/end also getting moved
> inside add_device_memory()/del_device_memory(). (just like for
> add/remove_memory)
> I wonder if kasan_ stuff actually requires this lock, or if it could
> also be somehow moved inside add_device_memory/del_device_memory.

Yes, that was my first approach, but then I saw that the kasan stuff is being
handled whithin those locks, so I was not sure and I backed off leaving the
mem_hotplug_begin/end where they were.

Maybe Jerome can shed some light and, and we can just handle the kasan stuff
out of the locks.

> Maybe shorten that a bit
> "HMM/devm memory does not have IORESOURCE_SYSTEM_RAM set. They use
>  devm_request_mem_region/devm_release_mem_region to add/release a
>  resource. Just back off here."

Uhm, fair enough.

> Any reason for these indirections?

I wanted to hide the internals in the memory_hotplug code.
I thought about removing them, but I finally left them.
If people think that we are better off without them, I can just
remove them.

> I guess for readability, this patch could be split up into several
> patches. E.g. factoring out of add_device_memory/del_device_memory,
> release_mem_region_adjustable change ...

Yes, really true.
But I wanted first to gather feedback mainly from HMM/devm people to see
if they saw an outright bug within the series because I am not so
familiar with that part of the code.

Feedback from Jerome/Dan will be appreciate as well to see if this is a good

But you are right, in the end, this will have to be slipt up into several
parts to ease the review.

Thanks for reviewing this David!
I will try to address your concerns.

Oscar Salvador

  reply	other threads:[~2018-08-22  7:50 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-17 15:41 [RFC v2 0/2] Do not touch pages in remove_memory path Oscar Salvador
2018-08-17 15:41 ` [RFC v2 1/2] mm/memory_hotplug: Add nid parameter to arch_remove_memory Oscar Salvador
2018-08-17 15:41 ` [RFC v2 2/2] mm/memory_hotplug: Shrink spanned pages when offlining memory Oscar Salvador
2018-08-21 13:17   ` David Hildenbrand
2018-08-22  7:50     ` Oscar Salvador [this message]
2018-08-22  8:11       ` David Hildenbrand
2018-08-29 23:09   ` Pasha Tatashin
2018-08-31 20:50     ` Oscar Salvador
2018-08-28 11:47 ` [RFC v2 0/2] Do not touch pages in remove_memory path Oscar Salvador
2018-08-29 17:04   ` Jerome Glisse

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