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From: David Hildenbrand <david@redhat.com>
To: Michal Hocko <mhocko@kernel.org>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Vlastimil Babka <vbabka@suse.cz>,
	Oscar Salvador <osalvador@suse.de>,
	Mel Gorman <mgorman@techsingularity.net>,
	Mike Rapoport <rppt@linux.ibm.com>,
	Dan Williams <dan.j.williams@intel.com>,
	Wei Yang <richard.weiyang@gmail.com>,
	Alexander Duyck <alexander.h.duyck@linux.intel.com>,
	Anshuman Khandual <anshuman.khandual@arm.com>,
	Pavel Tatashin <pavel.tatashin@microsoft.com>
Subject: Re: [PATCH v1 1/2] mm/page_alloc.c: Don't set pages PageReserved() when offlining
Date: Mon, 21 Oct 2019 17:54:35 +0200	[thread overview]
Message-ID: <91ecb9b7-4271-a3a7-2342-b0afd4c41606@redhat.com> (raw)
In-Reply-To: <20191021154712.GW9379@dhcp22.suse.cz>

On 21.10.19 17:47, Michal Hocko wrote:
> On Mon 21-10-19 17:39:36, David Hildenbrand wrote:
>> On 21.10.19 16:43, Michal Hocko wrote:
> [...]
>>> We still set PageReserved before onlining pages and that one should be
>>> good to go as well (memmap_init_zone).
>>> Thanks!
>>
>> memmap_init_zone() is called when onlining memory. There, set all pages to
>> reserved right now (on context == MEMMAP_HOTPLUG). We clear PG_reserved when
>> onlining a page to the buddy (e.g., generic_online_page). If we would online
>> a memory block with holes, we would want to keep all such pages
>> (!pfn_valid()) set to reserved. Also, there might be other side effects.
> 
> Isn't it sufficient to have those pages in a poisoned state? They are
> not onlined so their state is basically undefined anyway. I do not see
> how PageReserved makes this any better.

It is what people have been using for a long time. Memory hole -> 
PG_reserved. The memmap is valid, but people want to tell "this here is 
crap, don't look at it".

> 
> Also is the hole inside a hotplugable memory something we really have to
> care about. Has anybody actually seen a platform to require that?

That's what I was asking. I can see "support" for this was added 
basically right from the beginning. I'd say we rip that out and 
cleanup/simplify. I am not aware of a platform that requires this. 
Especially, memory holes on DIMMs (detected during boot) seem like an 
unlikely thing.


-- 

Thanks,

David / dhildenb


  reply	other threads:[~2019-10-21 15:54 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-21 14:19 [PATCH v1 0/2] mm: Memory offlining + page isolation cleanups David Hildenbrand
2019-10-21 14:19 ` [PATCH v1 1/2] mm/page_alloc.c: Don't set pages PageReserved() when offlining David Hildenbrand
2019-10-21 14:43   ` Michal Hocko
2019-10-21 15:39     ` David Hildenbrand
2019-10-21 15:47       ` Michal Hocko
2019-10-21 15:54         ` David Hildenbrand [this message]
2019-10-22  8:20           ` Michal Hocko
2019-10-22  8:23             ` David Hildenbrand
2019-10-22  8:58               ` Michal Hocko
2019-10-22  9:03                 ` David Hildenbrand
2019-10-21 14:19 ` [PATCH v1 2/2] mm/page_isolation.c: Convert SKIP_HWPOISON to MEMORY_OFFLINE David Hildenbrand
2019-10-21 15:02   ` Michal Hocko
2019-10-21 15:04     ` David Hildenbrand

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