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@xxxxxxxxxx> > Cc: Vasily Gorbik <gor@xxxxxxxxxxxxx> > Cc: Christian Borntraeger <borntraeger@xxxxxxxxxx> > Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx> > Cc: Philipp Rudo <prudo@xxxxxxxxxxxxx> > Cc: Gerald Schaefer <gerald.schaefer@xxxxxxxxxx> > Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxxxxx> > Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> Thanks applied
