From: Oscar Salvador <osalvador@suse.de>
To: Rashmica Gupta <rashmica.g@gmail.com>
Cc: David Hildenbrand <david@redhat.com>,
akpm@linux-foundation.org, mhocko@suse.com,
dan.j.williams@intel.com, pasha.tatashin@soleen.com,
Jonathan.Cameron@huawei.com, anshuman.khandual@arm.com,
vbabka@suse.cz, linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 0/5] Allocate memmap from hotadded memory
Date: Tue, 2 Jul 2019 09:48:18 +0200 [thread overview]
Message-ID: <20190702074806.GA26836@linux> (raw)
In-Reply-To: <9143f64391d11aa0f1988e78be9de7ff56e4b30b.camel@gmail.com>
On Tue, Jul 02, 2019 at 04:42:34PM +1000, Rashmica Gupta wrote:
> Hi David,
>
> Sorry for the late reply.
>
> On Wed, 2019-06-26 at 10:28 +0200, David Hildenbrand wrote:
> > On 26.06.19 10:15, Oscar Salvador wrote:
> > > On Wed, Jun 26, 2019 at 10:11:06AM +0200, David Hildenbrand wrote:
> > > > Back then, I already mentioned that we might have some users that
> > > > remove_memory() they never added in a granularity it wasn't
> > > > added. My
> > > > concerns back then were never fully sorted out.
> > > >
> > > > arch/powerpc/platforms/powernv/memtrace.c
> > > >
> > > > - Will remove memory in memory block size chunks it never added
> > > > - What if that memory resides on a DIMM added via
> > > > MHP_MEMMAP_DEVICE?
> > > >
> > > > Will it at least bail out? Or simply break?
> > > >
> > > > IOW: I am not yet 100% convinced that MHP_MEMMAP_DEVICE is save
> > > > to be
> > > > introduced.
> > >
> > > Uhm, I will take a closer look and see if I can clear your
> > > concerns.
> > > TBH, I did not try to use arch/powerpc/platforms/powernv/memtrace.c
> > > yet.
> > >
> > > I will get back to you once I tried it out.
> > >
> >
> > BTW, I consider the code in arch/powerpc/platforms/powernv/memtrace.c
> > very ugly and dangerous.
>
> Yes it would be nice to clean this up.
>
> > We should never allow to manually
> > offline/online pages / hack into memory block states.
> >
> > What I would want to see here is rather:
> >
> > 1. User space offlines the blocks to be used
> > 2. memtrace installs a hotplug notifier and hinders the blocks it
> > wants
> > to use from getting onlined.
> > 3. memory is not added/removed/onlined/offlined in memtrace code.
> >
>
> I remember looking into doing it a similar way. I can't recall the
> details but my issue was probably 'how does userspace indicate to
> the kernel that this memory being offlined should be removed'?
>
> I don't know the mm code nor how the notifiers work very well so I
> can't quite see how the above would work. I'm assuming memtrace would
> register a hotplug notifier and when memory is offlined from userspace,
> the callback func in memtrace would be called if the priority was high
> enough? But how do we know that the memory being offlined is intended
> for usto touch? Is there a way to offline memory from userspace not
> using sysfs or have I missed something in the sysfs interface?
>
> On a second read, perhaps you are assuming that memtrace is used after
> adding new memory at runtime? If so, that is not the case. If not, then
> would you be able to clarify what I'm not seeing?
Hi Rashmica,
let us go the easy way here.
Could you please explain:
1) How memtrace works
2) Why it was designed, what is the goal of the interface?
3) When it is supposed to be used?
I have seen a couple of reports in the past from people running memtrace
and failing to do so sometimes, and back then I could not grasp why people
was using it, or under which circumstances was nice to have.
So it would be nice to have a detailed explanation from the person who wrote
it.
Thanks
--
Oscar Salvador
SUSE L3
next prev parent reply other threads:[~2019-07-02 7:48 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 [this message]
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
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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