From: Anshuman Khandual <anshuman.khandual@arm.com>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: mark.rutland@arm.com, david@redhat.com, linux-mm@kvack.org,
arunks@codeaurora.org, cpandya@codeaurora.org,
ira.weiny@intel.com, will@kernel.org, steven.price@arm.com,
valentin.schneider@arm.com, suzuki.poulose@arm.com,
Robin.Murphy@arm.com, broonie@kernel.org, cai@lca.pw,
ard.biesheuvel@arm.com, dan.j.williams@intel.com,
linux-arm-kernel@lists.infradead.org, osalvador@suse.de,
steve.capper@arm.com, logang@deltatee.com,
linux-kernel@vger.kernel.org, James Morse <james.morse@arm.com>,
akpm@linux-foundation.org, mgorman@techsingularity.net
Subject: Re: [PATCH V9 2/2] arm64/mm: Enable memory hot remove
Date: Mon, 21 Oct 2019 15:25:08 +0530 [thread overview]
Message-ID: <6b5c96fe-cb3c-d0c2-e1f4-6ecd34be62a5@arm.com> (raw)
In-Reply-To: <f5581644-42b7-097e-6a86-ba7db9d0b544@arm.com>
On 10/21/2019 03:23 PM, Anshuman Khandual wrote:
>
> On 10/18/2019 03:18 PM, Catalin Marinas wrote:
>> On Fri, Oct 11, 2019 at 08:26:32AM +0530, Anshuman Khandual wrote:
>>> On 10/10/2019 05:04 PM, Catalin Marinas wrote:
>>>> Mark Rutland mentioned at some point that, as a preparatory patch to
>>>> this series, we'd need to make sure we don't hot-remove memory already
>>>> given to the kernel at boot. Any plans here?
>>> Hmm, this series just enables platform memory hot remove as required from
>>> generic memory hotplug framework. The path here is triggered either from
>>> remove_memory() or __remove_memory() which takes physical memory range
>>> arguments like (nid, start, size) and do the needful. arch_remove_memory()
>>> should never be required to test given memory range for anything including
>>> being part of the boot memory.
>> Assuming arch_remove_memory() doesn't (cannot) check, is there a risk on
> Platform can definitely enumerate boot memory ranges. But checking on it in
> arch_remove_memory() which deals with actual procedural details might not be
> ideal IMHO. Refusing a requested removal attempt should have been done up in
> the call chain. This will require making generic hot plug reject any removal
> request which falls within enumerated boot memory. IFAICS currently there is
> no generic way to remember which memory came as part of the boot process.
> Probably be a new MEMBLOCK flag will do.
>
>> arm64 that, for example, one removes memory available at boot and then
>> kexecs a new kernel? Does the kexec tool present the new kernel with the
>> original memory map?
> I dont know, probably James can help here. But as I had mentioned earlier,
> the callers of remove_memory() should be able to control that. ACPI should
> definitely be aware about which ranges were part of boot memory and refrain
> from removing any subset, if the platform is known to have problems with
> any subsequent kexec operation because the way boot memory map get used.
>
> Though I am not much aware about kexec internals, it should inherit the
> memory state at given point in time accommodating all previous memory hot
> and remove operations. As an example cloud environment scenario, memory
> resources might have increased or decreased during a guest lifetime, so
> when the guest needs to have new OS image why should not it have all the
> memory ? I dont know if it's feasible for the guest to expect previous hot
> add or remove operations to be played again after the kexec.
>
> There is another fundamental question here. Is there a notion of a minimum
> subset of boot memory which cannot be hot removed no matter what ? If yes,
> how that is being conveyed to the kernel currently ?
>
> The point is that all these need to be established between ACPI, EFI and
> kernel. AFAICS this problem is for MM subsystem (including the platform
s/is for/is not for/ ^^^^^^^^^^
next prev parent reply other threads:[~2019-10-21 9:55 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-09 8:21 [PATCH V9 0/2] arm64/mm: Enable memory hot remove Anshuman Khandual
2019-10-09 8:21 ` [PATCH V9 1/2] arm64/mm: Hold memory hotplug lock while walking for kernel page table dump Anshuman Khandual
2019-10-09 8:21 ` [PATCH V9 2/2] arm64/mm: Enable memory hot remove Anshuman Khandual
2019-10-10 11:34 ` Catalin Marinas
2019-10-11 2:56 ` Anshuman Khandual
2019-10-18 9:48 ` Catalin Marinas
2019-10-21 9:53 ` Anshuman Khandual
2019-10-21 9:55 ` Anshuman Khandual [this message]
2019-10-25 17:09 ` James Morse
2019-10-28 8:25 ` Anshuman Khandual
2019-11-04 3:57 ` Anshuman Khandual
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