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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. Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Gerald Schaefer <gerald.schaefer@de.ibm.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Vasily Gorbik <gor@linux.ibm.com> Cc: Christian Borntraeger <borntraeger@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> Link: https://lore.kernel.org/r/20200424083904.8587-1-david@redhat.com Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com> Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.