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Date: Wed, 8 Aug 2018 23:28:15 +0200
From: Oscar Salvador <osalvador@...hadventures.net>
To: Jerome Glisse <jglisse@...hat.com>
Cc: Michal Hocko <mhocko@...nel.org>, akpm@...ux-foundation.org,
dan.j.williams@...el.com, pasha.tatashin@...cle.com,
david@...hat.com, yasu.isimatu@...il.com, logang@...tatee.com,
dave.jiang@...el.com, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, Oscar Salvador <osalvador@...e.de>
Subject: Re: [RFC PATCH 2/3] mm/memory_hotplug: Create __shrink_pages and
move it to offline_pages
On Wed, Aug 08, 2018 at 12:58:15PM -0400, Jerome Glisse wrote:
> > If the former then I do not see any reason why we couldn't simply
> > refactor the code to expect a failure and drop the warning in that path.
>
> Referring to newer case ie calling release_mem_region_adjustable() for
> ZONE_DEVICE too. It seems i got my recollection wrong in the sense that
> the resource is properly register as MEM but still we do not want to
> release it because the device driver might still be using the resource
> without struct page. The lifetime of the resource as memory with struct
> page and the lifetime of the resource as something use by the device
> driver are not tie together. The latter can outlive the former.
>
> So when we hotremove ZONE_DEVICE we do not want to release the resource
> yet just to be on safe side and avoid some other driver/kernel component
> to decide to use that resource.
I checked the function that hot-removes the memory in HMM code.
hmm_devmem_pages_remove(), which gets called via hmm_devmem_remove(), is in charge
of hot-removing the memory.
Then, hmm_devmem_remove() will release the resource only if the resource is not of
type IORES_DESC_DEVICE_PUBLIC_MEMORY.
So I guess that there are cases(at least in HMM) where we release the resource when
hot-removing memory, but not always.
Looking at devm code, I could not see any place where we release the resource
when hot-removing memory.
So, if we are really left with such scenario, maybe the easiest way is to pass a parameter
from those paths to arch_remove_memory()->__remove_pages() to know
if we get called from device_functions, and so skip the call to release_mem_region_adjustable.
Thanks
--
Oscar Salvador
SUSE L3
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