On 24.04.20 10:12, 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 don't need a special memory notifier and can drop it. Repeating the
> above test with this patch results in the same behavior.
>
> 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>
> ---
> arch/s390/kernel/setup.c | 33 ---------------------------------
> 1 file changed, 33 deletions(-)
>
> diff --git a/arch/s390/kernel/setup.c b/arch/s390/kernel/setup.c
> index 0f0b140b5558..95d4fba0d811 100644
> --- a/arch/s390/kernel/setup.c
> +++ b/arch/s390/kernel/setup.c
> @@ -39,7 +39,6 @@
> #include <linux/kernel_stat.h>
> #include <linux/dma-contiguous.h>
> #include <linux/device.h>
> -#include <linux/notifier.h>
> #include <linux/pfn.h>
> #include <linux/ctype.h>
> #include <linux/reboot.h>
> @@ -591,35 +590,6 @@ static void __init setup_memory_end(void)
> pr_notice("The maximum memory size is %luMB\n", memory_end >> 20);
> }
>
> -#ifdef CONFIG_CRASH_DUMP
> -
> -/*
> - * When kdump is enabled, we have to ensure that no memory from
> - * the area [0 - crashkernel memory size] and
> - * [crashk_res.start - crashk_res.end] is set offline.
> - */
Re-reading that comment, I missed the [0 - crashkernel memory size]
part (for relocation IIRC). So we might want to keep checking for [0 -
crashkernel memory size] - will double check.
--
Thanks,
David / dhildenb
