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From: Christian Borntraeger <borntraeger@de.ibm.com>
To: David Hildenbrand <david@redhat.com>, linux-kernel@vger.kernel.org
Cc: linux-mm@kvack.org, linux-s390@vger.kernel.org,
	Heiko Carstens <heiko.carstens@de.ibm.com>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Martin Schwidefsky <schwidefsky@de.ibm.com>,
	Philipp Rudo <prudo@linux.ibm.com>,
	Gerald Schaefer <gerald.schaefer@de.ibm.com>,
	"Eric W . Biederman" <ebiederm@xmission.com>,
	Michal Hocko <mhocko@kernel.org>
Subject: Re: [PATCH v2] s390: simplify memory notifier for protecting kdump crash kernel area
Date: Thu, 14 May 2020 14:41:30 +0200	[thread overview]
Message-ID: <889669d5-5d5f-fe61-e269-1227a181d503@de.ibm.com> (raw)
In-Reply-To: <20200424083904.8587-1-david@redhat.com>

On 24.04.20 10:39, David Hildenbrand wrote:
> Assume we have a crashkernel area of 256MB reserved:
> 
> root@vm0:~# cat /proc/iomem
> 00000000-6fffffff : System RAM
>   0f258000-0fcfffff : Kernel code
>   0fd00000-101d10e3 : Kernel data
>   105b3000-1068dfff : Kernel bss
> 70000000-7fffffff : Crash kernel
> 
> This exactly corresponds to memory block 7 (memory block size is 256MB).
> Trying to offline that memory block results in:
> 
> root@vm0:~# echo "offline" > /sys/devices/system/memory/memory7/state
> -bash: echo: write error: Device or resource busy
> 
> [  128.458762] page:000003d081c00000 refcount:1 mapcount:0 mapping:00000000d01cecd4 index:0x0
> [  128.458773] flags: 0x1ffff00000001000(reserved)
> [  128.458781] raw: 1ffff00000001000 000003d081c00008 000003d081c00008 0000000000000000
> [  128.458781] raw: 0000000000000000 0000000000000000 ffffffff00000001 0000000000000000
> [  128.458783] page dumped because: unmovable page
> 
> The craskernel area is marked reserved in the bootmem allocator. This
> results in the memmap getting initialized (refcount=1, PG_reserved), but
> the pages are never freed to the page allocator.
> 
> So these pages look like allocated pages that are unmovable (esp.
> PG_reserved), and therefore, memory offlining fails early, when trying to
> isolate the page range.
> 
> We only have to care about the exchange area, make that clear.
> 
> Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
> Cc: Vasily Gorbik <gor@linux.ibm.com>
> Cc: Christian Borntraeger <borntraeger@de.ibm.com>
> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
> Cc: Philipp Rudo <prudo@linux.ibm.com>
> Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>
> Cc: Eric W. Biederman <ebiederm@xmission.com>
> Cc: Michal Hocko <mhocko@kernel.org>
> Signed-off-by: David Hildenbrand <david@redhat.com>

Thanks applied


      parent reply	other threads:[~2020-05-14 12:41 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-24  8:39 David Hildenbrand
2020-04-29 14:55 ` David Hildenbrand
2020-04-30 15:05   ` Gerald Schaefer
2020-05-14 12:41 ` Christian Borntraeger [this message]

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