Re: [PATCH -next v3 1/2] riscv: kdump: Implement crashkernel=X,[high,low]

[chenjiahao (C)]

On 2023/4/8 10:00, Leizhen (ThunderTown) wrote:
> On 2023/4/7 20:58, Leizhen (ThunderTown) wrote:
> > On 2023/4/7 20:03, Simon Horman wrote:
> > > On Fri, Apr 07, 2023 at 06:02:05AM +0800, Chen Jiahao wrote:
> > > > On riscv, the current crash kernel allocation logic is trying to
> > > > allocate within 32bit addressible memory region by default, if
> > > > failed, try to allocate without 4G restriction.
> > > >
> > > > In need of saving DMA zone memory while allocating a relatively large
> > > > crash kernel region, allocating the reserved memory top down in
> > > > high memory, without overlapping the DMA zone, is a mature solution.
> > > > Here introduce the parameter option crashkernel=X,[high,low].
> > > >
> > > > One can reserve the crash kernel from high memory above DMA zone range
> > > > by explicitly passing "crashkernel=X,high"; or reserve a memory range
> > > > below 4G with "crashkernel=X,low".
> > > >
> > > > Signed-off-by: Chen Jiahao <chenjiahao16@xxxxxxxxxx>
> > > ...
> > >
> > > > @@ -1180,14 +1206,37 @@ static void __init reserve_crashkernel(void)
> > > >   		return;
> > > >   	}
> > > >   
> > > > -	ret = parse_crashkernel(boot_command_line, memblock_phys_mem_size(),
> > > > +	ret = parse_crashkernel(cmdline, memblock_phys_mem_size(),
> > > >   				&crash_size, &crash_base);
> > > > -	if (ret || !crash_size)
> > > > +	if (ret == -ENOENT) {
> > > > +		/*
> > > > +		 * crashkernel=X,[high,low] can be specified or not, but
> > > > +		 * invalid value is not allowed.
> > > nit: Perhaps something like this would be easier to correlate with the
> > >       code that follows:
> > >
> > > 		/* Fallback to crashkernel=X,[high,low] */
> > The description "crashkernel=X,[high,low] can be specified or not" is not
> > correct, because crashkernel=X,high must be specified when walking into this
> > branch. So use Simon's comments or copy arm64's comments(it's written for
> > parse_crashkernel_low()).
> I rethink it a little bit, if it's relative to crashkernel=X[@offset],
> that's also true.
>
> Reviewed-by: Zhen Lei <thunder.leizhen@xxxxxxxxxx>

Sure, The commit should not be ambiguous like this, Simon's comment above is

a better option.


> > > > +		 */
> > > > +		ret = parse_crashkernel_high(cmdline, 0, &crash_size, &crash_base);
> > > > +		if (ret || !crash_size)
> > > > +			return;
> > > > +
> > > > +		/*
> > > > +		 * crashkernel=Y,low is valid only when crashkernel=X,high
> > > > +		 * is passed and high memory is reserved successful.
> > > nit: s/successful/successfully/
> > Seems like the whole "and high memory is reserved successful" needs to be deleted.
> > Only the dependency between the two boot options should be described here,
> > regardless of whether their memory is successfully allocated.

The comment here is imprecise, since there is absolutely no check whether

the allocation is successful before "parse_crashkernel_low"


> > > > +		 */
> > > > +		ret = parse_crashkernel_low(cmdline, 0, &crash_low_size, &crash_base);
> > > > +		if (ret == -ENOENT)
> > > > +			crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
> > > > +		else if (ret)
> > > > +			return;
> > > > +
> > > > +		search_start = search_low_max;
> > > > +	} else if (ret || !crash_size) {
> > > > +		/* Invalid argument value specified */
> > > >   		return;
> > > > +	}
> > > ...
> > > .
BR,

Jiahao