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From: Michal Hocko <mhocko@suse.com>
To: David Hildenbrand <david@redhat.com>
Cc: Oscar Salvador <osalvador@suse.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Anshuman Khandual <anshuman.khandual@arm.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	Pavel Tatashin <pasha.tatashin@soleen.com>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 1/5] mm,memory_hotplug: Allocate memmap from the added memory range
Date: Thu, 25 Mar 2021 15:34:28 +0100	[thread overview]
Message-ID: <YFyfdDAoWON6IoPL@dhcp22.suse.cz> (raw)
In-Reply-To: <062bc5d7-a83c-1c1a-7b77-9f043643f4fa@redhat.com>

On Thu 25-03-21 15:09:35, David Hildenbrand wrote:
> On 25.03.21 15:08, Michal Hocko wrote:
> > On Thu 25-03-21 13:40:45, David Hildenbrand wrote:
> > > On 25.03.21 13:35, Michal Hocko wrote:
> > > > On Thu 25-03-21 12:08:43, David Hildenbrand wrote:
> > > > > On 25.03.21 11:55, Oscar Salvador wrote:
> > [...]
> > > > > > - When moving the initialization/accounting to hot-add/hot-remove,
> > > > > >      the section containing the vmemmap pages will remain offline.
> > > > > >      It might get onlined once the pages get online in online_pages(),
> > > > > >      or not if vmemmap pages span a whole section.
> > > > > >      I remember (but maybe David rmemeber better) that that was a problem
> > > > > >      wrt. pfn_to_online_page() and hybernation/kdump.
> > > > > >      So, if that is really a problem, we would have to care of ot setting
> > > > > >      the section to the right state.
> > > > > 
> > > > > Good memory. Indeed, hibernation/kdump won't save the state of the vmemmap,
> > > > > because the memory is marked as offline and, thus, logically without any
> > > > > valuable content.

^^^^ THIS

> > > > 
> > > > Could you point me to the respective hibernation code please? I always
> > > > get lost in that area. Anyway, we do have the same problem even if the
> > > > whole accounting is handled during {on,off}lining, no?
> > > 
> > > kernel/power/snapshot.c:saveable_page().
> > 
> > Thanks! So this is as I've suspected. The very same problem is present
> > if the memory block is marked offline. So we need a solution here
> > anyway. One way to go would be to consider these vmemmap pages always
> > online. pfn_to_online_page would have to special case them but we would
> > need to identify them first. I used to have PageVmemmap or something
> > like that in my early attempt to do this.
> > 
> > That being said this is not an argument for one or the other aproach.
> > Both need fixing.
> 
> Can you elaborate? What is the issue there? What needs fixing?

offline section containing vmemmap will be lost during hibernation cycle
IIU the above correctly.
-- 
Michal Hocko
SUSE Labs


  reply	other threads:[~2021-03-25 14:34 UTC|newest]

Thread overview: 63+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-19  9:26 [PATCH v5 0/5] Allocate memmap from hotadded memory (per device) Oscar Salvador
2021-03-19  9:26 ` [PATCH v5 1/5] mm,memory_hotplug: Allocate memmap from the added memory range Oscar Salvador
2021-03-19 10:20   ` David Hildenbrand
2021-03-19 10:31     ` Oscar Salvador
2021-03-19 12:04       ` David Hildenbrand
2021-03-23 10:11   ` Michal Hocko
2021-03-24 10:12     ` Oscar Salvador
2021-03-24 12:03       ` Michal Hocko
2021-03-24 12:10         ` Michal Hocko
2021-03-24 12:23           ` David Hildenbrand
2021-03-24 12:37             ` Michal Hocko
2021-03-24 13:13               ` David Hildenbrand
2021-03-24 13:40                 ` Michal Hocko
2021-03-24 14:05                   ` David Hildenbrand
2021-03-24 13:27         ` Oscar Salvador
2021-03-24 14:42         ` Michal Hocko
2021-03-24 14:52           ` David Hildenbrand
2021-03-24 16:04             ` Michal Hocko
2021-03-24 19:16               ` David Hildenbrand
2021-03-25  8:07                 ` Oscar Salvador
2021-03-25  9:17                   ` Michal Hocko
2021-03-25 10:55                     ` Oscar Salvador
2021-03-25 11:08                       ` David Hildenbrand
2021-03-25 11:23                         ` Oscar Salvador
2021-03-25 12:35                         ` Michal Hocko
2021-03-25 12:40                           ` David Hildenbrand
2021-03-25 14:08                             ` Michal Hocko
2021-03-25 14:09                               ` David Hildenbrand
2021-03-25 14:34                                 ` Michal Hocko [this message]
2021-03-25 14:46                                   ` David Hildenbrand
2021-03-25 15:12                                     ` Michal Hocko
2021-03-25 15:19                                       ` David Hildenbrand
2021-03-25 15:35                                         ` Michal Hocko
2021-03-25 15:40                                           ` David Hildenbrand
2021-03-25 16:07                                           ` Michal Hocko
2021-03-25 16:20                                             ` David Hildenbrand
2021-03-25 16:36                                               ` Michal Hocko
2021-03-25 16:47                                                 ` Michal Hocko
2021-03-25 16:55                                                   ` David Hildenbrand
2021-03-25 22:06                                                   ` Oscar Salvador
2021-03-26  8:35                                                     ` Michal Hocko
2021-03-26  8:52                                                       ` David Hildenbrand
2021-03-26  8:57                                                         ` Oscar Salvador
2021-03-26 12:15                                                           ` Oscar Salvador
2021-03-26 13:36                                                             ` David Hildenbrand
2021-03-26 14:38                                                         ` Michal Hocko
2021-03-26 14:53                                                           ` David Hildenbrand
2021-03-26 15:31                                                             ` Michal Hocko
2021-03-26 16:03                                                               ` David Hildenbrand
2021-03-26  8:55                                                       ` Oscar Salvador
2021-03-26  9:11                                                         ` Michal Hocko
2021-03-25 18:08                                                 ` David Hildenbrand
2021-03-25 12:26                       ` Michal Hocko
2021-03-25 14:02                         ` Oscar Salvador
2021-03-25 14:40                           ` Michal Hocko
2021-03-19  9:26 ` [PATCH v5 2/5] acpi,memhotplug: Enable MHP_MEMMAP_ON_MEMORY when supported Oscar Salvador
2021-03-23 10:40   ` Michal Hocko
2021-03-19  9:26 ` [PATCH v5 3/5] mm,memory_hotplug: Add kernel boot option to enable memmap_on_memory Oscar Salvador
2021-03-23 10:47   ` Michal Hocko
2021-03-24  8:45     ` Oscar Salvador
2021-03-24  9:02       ` Michal Hocko
2021-03-19  9:26 ` [PATCH v5 4/5] x86/Kconfig: Introduce ARCH_MHP_MEMMAP_ON_MEMORY_ENABLE Oscar Salvador
2021-03-19  9:26 ` [PATCH v5 5/5] arm64/Kconfig: " Oscar Salvador

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