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From: Michal Hocko <mhocko@kernel.org>
To: David Hildenbrand <david@redhat.com>
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 09:24:30 +0200	[thread overview]
Message-ID: <20190801072430.GF11627@dhcp22.suse.cz> (raw)
In-Reply-To: <9bcbd574-7e23-5cfe-f633-646a085f935a@redhat.com>

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?
-- 
Michal Hocko
SUSE Labs


  reply	other threads:[~2019-08-01  7:24 UTC|newest]

Thread overview: 58+ 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 10:28   ` David Hildenbrand
2019-06-26  9:48     ` 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
2019-07-02  8:52               ` Rashmica Gupta
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 [this message]
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
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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