Re: [PATCH] kexec: Account crashk_low_res to kexec_crash_size

[Dave Young]

Hi Xunlei,

On 08/13/16 at 04:26pm, Xunlei Pang wrote:
> "/sys/kernel/kexec_crash_size" only includes crashk_res, it
> is fine in most cases, but sometimes we have crashk_low_res.
> For example, when "crashkernel=size[KMG],high" combined with
> "crashkernel=size[KMG],low" is used for 64-bit x86.
> 
> Let "/sys/kernel/kexec_crash_size" reflect all the reserved
> memory including crashk_low_res, this is more understandable
> from its naming.

Maybe export another file for the kexec_crash_low_size so that
we can clearly get how much the low area is.

> 
> Although we can get all the crash memory from "/proc/iomem"
> by filtering all "Crash kernel" keyword, it is more convenient
> to utilize this file, and the two ways should stay consistent.

Shrink low area does not make much sense, one may either use it or
shrink it to 0.

Actually think more about it, the crashk_low is only for x86,
it might be even better to move it to x86 code instead of in
common code.

Opinion?

Thanks
Dave
> 
> Note that write to "/sys/kernel/kexec_crash_size" is to shrink
> the reserved memory, and we want to shrink crashk_res only.
> So we add some additional check in crash_shrink_memory() since
> crashk_low_res now is involved.
> 
> Signed-off-by: Xunlei Pang <xlpang@xxxxxxxxxx>
> ---
>  kernel/kexec_core.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
> index 5616755..d5ae780 100644
> --- a/kernel/kexec_core.c
> +++ b/kernel/kexec_core.c
> @@ -932,6 +932,8 @@ size_t crash_get_memory_size(void)
>  	mutex_lock(&kexec_mutex);
>  	if (crashk_res.end != crashk_res.start)
>  		size = resource_size(&crashk_res);
> +	if (crashk_low_res.end != crashk_low_res.start)
> +		size += resource_size(&crashk_low_res);
>  	mutex_unlock(&kexec_mutex);
>  	return size;
>  }
> @@ -949,7 +951,7 @@ int crash_shrink_memory(unsigned long new_size)
>  {
>  	int ret = 0;
>  	unsigned long start, end;
> -	unsigned long old_size;
> +	unsigned long low_size, old_size;
>  	struct resource *ram_res;
>  
>  	mutex_lock(&kexec_mutex);
> @@ -958,6 +960,17 @@ int crash_shrink_memory(unsigned long new_size)
>  		ret = -ENOENT;
>  		goto unlock;
>  	}
> +
> +	start = crashk_low_res.start;
> +	end = crashk_low_res.end;
> +	low_size = (end == 0) ? 0 : end - start + 1;
> +	/* Do not shrink crashk_low_res. */
> +	if (new_size <= low_size) {
> +		ret = -EINVAL;
> +		goto unlock;
> +	}
> +
> +	new_size -= low_size;
>  	start = crashk_res.start;
>  	end = crashk_res.end;
>  	old_size = (end == 0) ? 0 : end - start + 1;
> -- 
> 1.8.3.1
> 
> 
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