linux-kernel - Re: [PATCH] arm64: kdump: Do not allocate crash low memory if not needed

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Message-ID: <20220511100623.GF122876@MiWiFi-R3L-srv>
Date:   Wed, 11 May 2022 18:06:23 +0800
From:   Baoquan He <bhe@...hat.com>
To:     "Leizhen (ThunderTown)" <thunder.leizhen@...wei.com>
Cc:     Dave Young <dyoung@...hat.com>, Vivek Goyal <vgoyal@...hat.com>,
        kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Feng Zhou <zhoufeng.zf@...edance.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Chen Zhou <dingguo.cz@...group.com>,
        John Donnelly <John.p.donnelly@...cle.com>,
        Dave Kleikamp <dave.kleikamp@...cle.com>
Subject: Re: [PATCH] arm64: kdump: Do not allocate crash low memory if not
 needed

On 05/11/22 at 05:50pm, Leizhen (ThunderTown) wrote:
> 
> 
> On 2022/5/11 17:06, Baoquan He wrote:
> > On 05/11/22 at 11:20am, Zhen Lei wrote:
> >> When "crashkernel=X,high" is specified, the specified "crashkernel=Y,low"
> >> memory is not required in the following corner cases:
> >> 1. If both CONFIG_ZONE_DMA and CONFIG_ZONE_DMA32 are disabled, it means
> >>    that the devices can access any memory.
> >> 2. If the system memory is small, the crash high memory may be allocated
> >>    from the DMA zones. If that happens, there's no need to allocate
> >>    another crash low memory because there's already one.
> >>
> >> Add condition '(crash_base >= CRASH_ADDR_LOW_MAX)' to determine whether
> >> the 'high' memory is allocated above DMA zones. Note: when both
> >> CONFIG_ZONE_DMA and CONFIG_ZONE_DMA32 are disabled, the entire physical
> >> memory is DMA accessible, CRASH_ADDR_LOW_MAX equals 'PHYS_MASK + 1'.
> >>
> >> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
> >> ---
> >>  Documentation/admin-guide/kernel-parameters.txt | 5 +++--
> >>  arch/arm64/mm/init.c                            | 3 ++-
> >>  2 files changed, 5 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> >> index f6ff55840751a78..1b543c3109f4851 100644
> >> --- a/Documentation/admin-guide/kernel-parameters.txt
> >> +++ b/Documentation/admin-guide/kernel-parameters.txt
> >> @@ -823,7 +823,7 @@
> >>  			low memory is needed to make sure DMA buffers for 32-bit
> >>  			devices won't run out. Kernel would try to allocate
> >>  			at least 256M below 4G automatically.
> >> -			This one let user to specify own low range under 4G
> >> +			This one lets the user specify own low range under 4G
> >                         ~ This one let users specify own low range ...
> > 
> > Other than this nitpick, LGTM
> 
> This is Catalin's response a few days ago:
> Slightly more correct is "This one lets the user specify..."
> 
> I didn't googled "This one lets", but I googled "It lets". I think he wrote it right.
> 
> Both "the user" and "users" seem to be right.

Yeah, I forgot the 'this one lets' part, and I am fine too with the 'the
use'if it's right. So please ignore the comment.

> 
> 
> > 
> > Acked-by: Baoquan He <bhe@...hat.com>
> > 
> >>  			for second kernel instead.
> >>  			0: to disable low allocation.
> >>  			It will be ignored when crashkernel=X,high is not used
> >> @@ -832,7 +832,8 @@
> >>  			[KNL, ARM64] range in low memory.
> >>  			This one lets the user specify a low range in the
> >>  			DMA zone for the crash dump kernel.
> >> -			It will be ignored when crashkernel=X,high is not used.
> >> +			It will be ignored when crashkernel=X,high is not used
> >> +			or memory reserved is located in the DMA zones.
> >>  
> >>  	cryptomgr.notests
> >>  			[KNL] Disable crypto self-tests
> >> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> >> index 18ba66c90991ea0..ac510fb6a2c0189 100644
> >> --- a/arch/arm64/mm/init.c
> >> +++ b/arch/arm64/mm/init.c
> >> @@ -170,7 +170,8 @@ static void __init reserve_crashkernel(void)
> >>  		return;
> >>  	}
> >>  
> >> -	if (crash_low_size && reserve_crashkernel_low(crash_low_size)) {
> >> +	if ((crash_base >= CRASH_ADDR_LOW_MAX) &&
> >> +	     crash_low_size && reserve_crashkernel_low(crash_low_size)) {
> >>  		memblock_phys_free(crash_base, crash_size);
> >>  		return;
> >>  	}
> >> -- 
> >> 2.25.1
> >>
> > 
> > .
> > 
> 
> -- 
> Regards,
>   Zhen Lei
>