From: David Hildenbrand <david@redhat.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: Rashmica Gupta <rashmica.g@gmail.com>,
Oscar Salvador <osalvador@suse.de>,
Andrew Morton <akpm@linux-foundation.org>,
Dan Williams <dan.j.williams@intel.com>,
pasha.tatashin@soleen.com, Jonathan.Cameron@huawei.com,
anshuman.khandual@arm.com, Vlastimil Babka <vbabka@suse.cz>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 0/5] Allocate memmap from hotadded memory
Date: Thu, 1 Aug 2019 09:50:29 +0200 [thread overview]
Message-ID: <7c12f0b1-61a5-ed6f-2c64-4058e47860a3@redhat.com> (raw)
In-Reply-To: <20190801073407.GG11627@dhcp22.suse.cz>
On 01.08.19 09:34, Michal Hocko wrote:
> On Thu 01-08-19 09:26:35, David Hildenbrand wrote:
>> On 01.08.19 09:24, Michal Hocko wrote:
>>> On Thu 01-08-19 09:18:47, David Hildenbrand wrote:
>>>> On 01.08.19 09:17, Michal Hocko wrote:
>>>>> On Thu 01-08-19 09:06:40, Rashmica Gupta wrote:
>>>>>> On Wed, 2019-07-31 at 14:08 +0200, Michal Hocko wrote:
>>>>>>> On Tue 02-07-19 18:52:01, Rashmica Gupta wrote:
>>>>>>> [...]
>>>>>>>>> 2) Why it was designed, what is the goal of the interface?
>>>>>>>>> 3) When it is supposed to be used?
>>>>>>>>>
>>>>>>>>>
>>>>>>>> There is a hardware debugging facility (htm) on some power chips.
>>>>>>>> To use
>>>>>>>> this you need a contiguous portion of memory for the output to be
>>>>>>>> dumped
>>>>>>>> to - and we obviously don't want this memory to be simultaneously
>>>>>>>> used by
>>>>>>>> the kernel.
>>>>>>>
>>>>>>> How much memory are we talking about here? Just curious.
>>>>>>
>>>>>> From what I've seen a couple of GB per node, so maybe 2-10GB total.
>>>>>
>>>>> OK, that is really a lot to keep around unused just in case the
>>>>> debugging is going to be used.
>>>>>
>>>>> I am still not sure the current approach of (ab)using memory hotplug is
>>>>> ideal. Sure there is some overlap but you shouldn't really need to
>>>>> offline the required memory range at all. All you need is to isolate the
>>>>> memory from any existing user and the page allocator. Have you checked
>>>>> alloc_contig_range?
>>>>>
>>>>
>>>> Rashmica mentioned somewhere in this thread that the virtual mapping
>>>> must not be in place, otherwise the HW might prefetch some of this
>>>> memory, leading to errors with memtrace (which checks that in HW).
>>>
>>> Does anything prevent from unmapping the pfn range from the direct
>>> mapping?
>>
>> I am not sure about the implications of having
>> pfn_valid()/pfn_present()/pfn_online() return true but accessing it
>> results in crashes. (suspend, kdump, whatever other technology touches
>> online memory)
>
> If those pages are marked as Reserved then nobody should be touching
> them anyway.
Which is not true as I remember we already discussed - I even documented
what PG_reserved can mean after that discussion in page-flags.h (e.g.,
memmap of boot memory) - that's why we introduced PG_offline after all.
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2019-08-01 7:50 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-25 7:52 [PATCH v2 0/5] Allocate memmap from hotadded memory Oscar Salvador
2019-06-25 7:52 ` [PATCH v2 1/5] drivers/base/memory: Remove unneeded check in remove_memory_block_devices Oscar Salvador
2019-06-25 8:01 ` David Hildenbrand
2019-06-25 8:03 ` David Hildenbrand
2019-06-25 8:09 ` Oscar Salvador
2019-06-25 8:27 ` David Hildenbrand
2019-06-25 7:52 ` [PATCH v2 2/5] mm,memory_hotplug: Introduce MHP_VMEMMAP_FLAGS Oscar Salvador
2019-06-25 8:31 ` David Hildenbrand
2019-07-24 20:11 ` Dan Williams
2019-07-24 21:36 ` osalvador
2019-07-25 9:27 ` Oscar Salvador
2019-07-25 9:30 ` David Hildenbrand
2019-07-25 9:40 ` Oscar Salvador
2019-07-25 10:04 ` David Hildenbrand
2019-07-25 10:13 ` Oscar Salvador
2019-07-25 10:15 ` David Hildenbrand
2019-06-25 7:52 ` [PATCH v2 3/5] mm,memory_hotplug: Introduce Vmemmap page helpers Oscar Salvador
2019-06-25 7:52 ` [PATCH v2 4/5] mm,memory_hotplug: allocate memmap from the added memory range for sparse-vmemmap Oscar Salvador
2019-06-25 8:49 ` David Hildenbrand
2019-06-26 8:13 ` Oscar Salvador
2019-06-26 8:15 ` David Hildenbrand
2019-06-26 8:17 ` Anshuman Khandual
2019-06-26 8:28 ` Oscar Salvador
2019-07-24 21:49 ` Dan Williams
2019-06-25 7:52 ` [PATCH v2 5/5] mm,memory_hotplug: Allow userspace to enable/disable vmemmap Oscar Salvador
2019-06-25 8:25 ` [PATCH v2 0/5] Allocate memmap from hotadded memory David Hildenbrand
2019-06-25 8:33 ` David Hildenbrand
2019-06-26 8:03 ` Oscar Salvador
2019-06-26 8:11 ` David Hildenbrand
2019-06-26 8:15 ` Oscar Salvador
2019-06-26 8:27 ` Oscar Salvador
2019-06-26 8:37 ` David Hildenbrand
2019-06-26 8:28 ` David Hildenbrand
2019-07-02 6:42 ` Rashmica Gupta
2019-07-02 7:48 ` Oscar Salvador
[not found] ` <CAC6rBskRyh5Tj9L-6T4dTgA18H0Y8GsMdC-X5_0Jh1SVfLLYtg@mail.gmail.com>
2019-07-10 1:14 ` Rashmica Gupta
2019-07-31 12:08 ` Michal Hocko
2019-07-31 23:06 ` Rashmica Gupta
2019-08-01 7:17 ` Michal Hocko
2019-08-01 7:18 ` David Hildenbrand
2019-08-01 7:24 ` Michal Hocko
2019-08-01 7:26 ` David Hildenbrand
2019-08-01 7:31 ` David Hildenbrand
2019-08-01 7:39 ` Michal Hocko
2019-08-01 7:48 ` Michal Hocko
2019-08-01 9:18 ` David Hildenbrand
2019-08-01 7:34 ` Michal Hocko
2019-08-01 7:50 ` David Hildenbrand [this message]
2019-08-01 8:04 ` Michal Hocko
2019-07-16 12:28 ` David Hildenbrand
2019-07-29 5:42 ` Rashmica Gupta
2019-07-29 8:06 ` David Hildenbrand
2019-07-30 7:08 ` Rashmica Gupta
2019-07-31 2:21 ` Rashmica Gupta
2019-07-31 9:39 ` David Hildenbrand
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