linux-kernel - Re: [PATCH 2/2] arm64/kdump: add code comments for crashkernel reservation cases

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Date:   Tue, 24 Jan 2023 10:49:42 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Simon Horman <horms@...nel.org>
Cc:     linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, catalin.marinas@....com,
        will@...nel.org, thunder.leizhen@...wei.com,
        John.p.donnelly@...cle.com, wangkefeng.wang@...wei.com
Subject: Re: [PATCH 2/2] arm64/kdump: add code comments for crashkernel
 reservation cases

On 01/20/23 at 10:02am, Simon Horman wrote:
> On Tue, Jan 17, 2023 at 11:49:21AM +0800, Baoquan He wrote:
> > This will help understand codes on crashkernel reservations on arm64.
> 
> FWIIW, I think you can fold this into the first patch.

Sure, will do.

I folded this into patch 1 at the very beginning. Then felt the added
code comments add lines of change and make the code change not so
straightforward. I admit it's from personal feeling. 

> 
> And, although I have no good idea at this moment, I do wonder
> if the logic can be simplified - I for one really needed the
> comments to understand the retry logic.

Got it. I will consider if I can improve the logic readability. Thanks.

> 
> > Signed-off-by: Baoquan He <bhe@...hat.com>
> > ---
> >  arch/arm64/mm/init.c | 13 +++++++++++++
> >  1 file changed, 13 insertions(+)
> > 
> > diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> > index 26a05af2bfa8..f88ad17cb20d 100644
> > --- a/arch/arm64/mm/init.c
> > +++ b/arch/arm64/mm/init.c
> > @@ -177,6 +177,10 @@ static void __init reserve_crashkernel(void)
> >  	crash_base = memblock_phys_alloc_range(crash_size, CRASH_ALIGN,
> >  					       search_base, crash_max);
> >  	if (!crash_base) {
> > +		/*
> > +		 * For crashkernel=size[KMG]@offset[KMG], print out failure
> > +		 * message if can't reserve the specified region.
> > +		 */
> >  		if (fixed_base) {
> >  			pr_warn("cannot reserve crashkernel region [0x%llx-0x%llx]\n",
> >  				search_base, crash_max);
> > @@ -188,6 +192,11 @@ static void __init reserve_crashkernel(void)
> >  		 * high memory, the minimum required low memory will be
> >  		 * reserved later.
> >  		 */
> > +		/*
> > +		 * For crashkernel=size[KMG], if the first attempt was for
> > +		 * low memory, fall back to high memory, the minimum required
> > +		 * low memory will be reserved later.
> > +		 */
> 
> I think this duplicates the preceding comment.
> Perhaps just replace the earlier comment with this one.
> 
> >  		if (!high && crash_max == CRASH_ADDR_LOW_MAX) {
> >  			crash_max = CRASH_ADDR_HIGH_MAX;
> >  			search_base = CRASH_ADDR_LOW_MAX;
> > @@ -195,6 +204,10 @@ static void __init reserve_crashkernel(void)
> >  			goto retry;
> >  		}
> >  
> > +		/*
> > +		 * For crashkernel=size[KMG],high, if the first attempt was for
> > +		 * high memory, fall back to low memory.
> > +		 */
> >  		if (high && (crash_max == CRASH_ADDR_HIGH_MAX)) {
> >  			crash_max = CRASH_ADDR_LOW_MAX;
> >  			search_base = 0;
> > -- 
> > 2.34.1
> > 
> > 
> > _______________________________________________
> > kexec mailing list
> > kexec@...ts.infradead.org
> > http://lists.infradead.org/mailman/listinfo/kexec
> > 
> 
> _______________________________________________
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> kexec@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/kexec
> 

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