linux-kernel - Re: [PATCH] x86, kdump: crashkernel=X try to reserve below 896M first, then try below 4G, then MAXMEM

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Message-ID: <20131028064315.GC3033@dhcp16-109.nay.redhat.com>
Date:	Mon, 28 Oct 2013 14:43:15 +0800
From:	WANG Chao <chaowang@...hat.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Pekka Enberg <penberg@...nel.org>,
	Jacob Shin <jacob.shin@....com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vivek Goyal <vgoyal@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86, kdump: crashkernel=X try to reserve below 896M
 first, then try below 4G, then MAXMEM

On 10/24/13 at 12:04pm, Yinghai Lu wrote:
> On Mon, Oct 14, 2013 at 4:46 AM, WANG Chao <chaowang@...hat.com> wrote:
> > Now crashkernel=X will fail out if there's not enough memory at
> > low (below 896M). What makes sense for crashkernel=X would be:
> >
> >  - First try to reserve X below 896M (for being compatible with old
> >    kexec-tools).
> >  - If fails, try to reserve X below 4G (swiotlb need to stay below 4G).
> >  - If fails, try to reserve X from MAXMEM top down.
> >
> > diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
> > index f0de629..38e6c1f 100644
> > --- a/arch/x86/kernel/setup.c
> > +++ b/arch/x86/kernel/setup.c
> > @@ -593,6 +593,20 @@ static void __init reserve_crashkernel(void)
> >                                         high ? CRASH_KERNEL_ADDR_HIGH_MAX :
> >                                                CRASH_KERNEL_ADDR_LOW_MAX,
> >                                         crash_size, alignment);
> > +               /*
> > +                * crashkernel=X reserve below 896M fails? Try below 4G
> > +                */
> > +               if (!high && !crash_base)
> > +                       crash_base = memblock_find_in_range(alignment,
> > +                                               (1ULL << 32),
> > +                                               crash_size, alignment);
> 
> Another problem, it would allocate range in [0,4g) for 32bit,
> if the user have crashkernel=512M or plus.

Yes, should use #ifdef CONFIG_X86_64 .. #endif.
Thanks for pointing this out.

WANG Chao

> 
> > +               /*
> > +                * crashkernel=X reserve below 4G fails? Try MAXMEM
> > +                */
> > +               if (!high && !crash_base)
> > +                       crash_base = memblock_find_in_range(alignment,
> > +                                               CRASH_KERNEL_ADDR_HIGH_MAX,
> > +                                               crash_size, alignment);
> >
> >                 if (!crash_base) {
> >                         pr_info("crashkernel reservation failed - No suitable area found.\n");
> 
> 
> Yinghai
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