linux-kernel - Re: [PATCH v12 9/9] kdump: update Documentation about crashkernel

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Date:   Wed, 7 Oct 2020 17:24:53 +0100
From:   Catalin Marinas <catalin.marinas@....com>
To:     chenzhou <chenzhou10@...wei.com>
Cc:     will@...nel.org, james.morse@....com, tglx@...utronix.de,
        mingo@...hat.com, dyoung@...hat.com, bhe@...hat.com,
        corbet@....net, John.P.donnelly@...cle.com,
        prabhakar.pkin@...il.com, bhsharma@...hat.com, horms@...ge.net.au,
        robh+dt@...nel.org, arnd@...db.de, nsaenzjulienne@...e.de,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kexec@...ts.infradead.org, linux-doc@...r.kernel.org,
        guohanjun@...wei.com, xiexiuqi@...wei.com, huawei.libin@...wei.com,
        wangkefeng.wang@...wei.com
Subject: Re: [PATCH v12 9/9] kdump: update Documentation about crashkernel

On Tue, Oct 06, 2020 at 10:10:54AM +0800, chenzhou wrote:
> On 2020/10/6 1:19, Catalin Marinas wrote:
> > On Mon, Sep 07, 2020 at 09:47:45PM +0800, Chen Zhou wrote:
> >> diff --git a/Documentation/admin-guide/kdump/kdump.rst b/Documentation/admin-guide/kdump/kdump.rst
> >> index 2da65fef2a1c..549611abc581 100644
> >> --- a/Documentation/admin-guide/kdump/kdump.rst
> >> +++ b/Documentation/admin-guide/kdump/kdump.rst
> > [...]
> >> @@ -316,8 +325,18 @@ Boot into System Kernel
> >>     kernel will automatically locate the crash kernel image within the
> >>     first 512MB of RAM if X is not given.
> >>  
> >> -   On arm64, use "crashkernel=Y[@X]".  Note that the start address of
> >> -   the kernel, X if explicitly specified, must be aligned to 2MiB (0x200000).
> >> +   On arm64, use "crashkernel=X" to try low allocation in DMA zone, and
> >> +   fall back to high allocation if it fails. And go for high allocation
> >> +   directly if the required size is too large.
> >> +   We can also use "crashkernel=X,high" to select a high region above
> >> +   DMA zone, which also tries to allocate at least 256M low memory in
> >> +   DMA zone automatically.
> >> +   "crashkernel=Y,low" can be used to allocate specified size low memory
> >> +   in DMA zone.
> >> +   For non-RPi4 platforms, change DMA zone memtioned above to DMA32 zone.
> > I don't think we should mention non-RPi4 explicitly here. I don't even
> > understand what the suggestion is since the only way is to disable
> > ZONE_DMA in the kernel config. I'd just stick to ZONE_DMA description
> > here.
> How about like this:
> If the kernel config ZONE_DMA is disabled, just try low allocation in DMA32 zone
> and high allocation above DMA32 zone.

Something like: "allocate 256M low memory in the DMA zone automatically
(or the DMA32 zone if CONFIG_ZONE_DMA is disabled)".

I'd keep it short.

-- 
Catalin