linux-kernel - Re: [PATCH -next v2 1/2] riscv: kdump: Implement crashkernel=X,[high,low]

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Date:   Fri, 31 Mar 2023 07:32:54 +0800
From:   Baoquan He <bhe@...hat.com>
To:     "chenjiahao (C)" <chenjiahao16@...wei.com>
Cc:     paul.walmsley@...ive.com, palmer@...belt.com,
        conor.dooley@...rochip.com, guoren@...nel.org, heiko@...ech.de,
        bjorn@...osinc.com, alex@...ti.fr, akpm@...ux-foundation.org,
        atishp@...osinc.com, thunder.leizhen@...wei.com, horms@...nel.org,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
        kexec@...ts.infradead.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH -next v2 1/2] riscv: kdump: Implement
 crashkernel=X,[high,low]

On 03/30/23 at 09:40pm, chenjiahao (C) wrote:
......
> Agreed, I will clean this up later in next version.
> > > +		if (ret || !crash_size)
> > > +			return;
> > > +
> > > +		/*
> > > +		 * crashkernel=Y,low is valid only when crashkernel=X,high
> > > +		 * is passed and high memory is reserved successful.
> > > +		 */
> > > +		ret = parse_crashkernel_low(boot_command_line, 0, &crash_low_size, &crash_base);
> > > +		if (ret == -ENOENT)
> > > +			crash_low_size = DEFAULT_CRASH_KERNEL_LOW_SIZE;
> > > +		else if (ret)
> > > +			return;
> > > +
> > > +		search_start = dma32_phys_limit;
> > > +	} else if (ret || !crash_size) {
> > > +		/* Invalid argument value specified */
> > >   		return;
> > > +	}
> > >   	crash_size = PAGE_ALIGN(crash_size);
> > > @@ -1201,16 +1246,26 @@ static void __init reserve_crashkernel(void)
> > >   	 */
> > >   	crash_base = memblock_phys_alloc_range(crash_size, PMD_SIZE,
> > >   					       search_start,
> > > -					       min(search_end, (unsigned long) SZ_4G));
> > > +					       min(search_end, (unsigned long)dma32_phys_limit));
> > >   	if (crash_base == 0) {
> > The above conditional check isn't right. If crashkernel=size@...set
> > specified, the reservation failure won't trigger retry. This seems to be
> > originally introduced by old commit, while this need be fixed firstly.
> 
> Just a little curious about the rule to cope with this specific case. If
> "crashkernel=size@...set" was passed
> 
> but reserve failed, should try again to allocate in high memory, regardless
> the specified size@...set,
> 
> or just throw a warning and return? Since I noticed the current logic here
> on Arm64 is to check if !fixed_base first

Yeah, we need mark the "crashkernel=size@...set" case and avoid to
retry. Because you won't succeed if  memblock has already failed to
reserve an unavailable memory region, retry is meaningless. This has
been done in x86, arm64.