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Date:   Tue, 13 Aug 2019 10:54:41 +0800
From:   Dave Young <dyoung@redhat.com>
To:     Michal Hocko <mhocko@kernel.org>
Cc:     Paul Menzel <pmenzel@molgen.mpg.de>, linux-pci@vger.kernel.org,
        =?iso-8859-1?Q?J=F6rg_R=F6del?= <joro@8bytes.org>,
        "x86@kernel.org" <x86@kernel.org>, kexec@lists.infradead.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        iommu@lists.linux-foundation.org, kasong@redhat.com,
        lijiang@redhat.com, Donald Buczek <buczek@molgen.mpg.de>
Subject: Re: Crash kernel with 256 MB reserved memory runs into OOM condition
Message-ID: <20190813025441.GA2979@dhcp-128-65.nay.redhat.com>
References: <d65e4a42-1962-78c6-1b5a-65cb70529d62@molgen.mpg.de>
 <20190812095029.GE5117@dhcp22.suse.cz>
 <20190813024317.GA2862@dhcp-128-65.nay.redhat.com>
 <20190813024600.GA2944@dhcp-128-65.nay.redhat.com>
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On 08/13/19 at 10:46am, Dave Young wrote:
> Add more cc.
> On 08/13/19 at 10:43am, Dave Young wrote:
> > Hi,
> > 
> > On 08/12/19 at 11:50am, Michal Hocko wrote:
> > > On Mon 12-08-19 11:42:33, Paul Menzel wrote:
> > > > Dear Linux folks,
> > > > 
> > > > 
> > > > On a Dell PowerEdge R7425 with two AMD EPYC 7601 (total 128 threads) and
> > > > 1 TB RAM, the crash kernel with 256 MB of space reserved crashes.
> > > > 
> > > > Please find the messages of the normal and the crash kernel attached.
> > > 
> > > You will need more memory to reserve for the crash kernel because ...
> > > 
> > > > [    4.548703] Node 0 DMA free:484kB min:4kB low:4kB high:4kB active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0kB writepending:0kB present:568kB managed:484kB mlocked:0kB kernel_stack:0kB pagetables:0kB bounce:0kB free_pcp:0kB local_pcp:0kB free_cma:0kB
> > > > [    4.573612] lowmem_reserve[]: 0 125 125 125
> > > > [    4.577799] Node 0 DMA32 free:1404kB min:1428kB low:1784kB high:2140kB active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:15720kB writepending:0kB present:261560kB managed:133752kB mlocked:0kB kernel_stack:2496kB pagetables:0kB bounce:0kB free_pcp:212kB local_pcp:212kB free_cma:0kB
> > > 
> > > ... the memory is really depleted and nothing to be reclaimed (no anon.
> > > file pages) Look how tht free memory is below min watermark (node zone DMA has
> > > lowmem protection for GFP_KERNEL allocation).
> > 
> > We found similar issue on our side while working on kdump on SME enabled
> > systemd.  Kairui is working on some patches.
> > 
> > Actually on those SME/SEV enabled machines, swiotlb is enabled
> > automatically so at least we need extra 64M+ memory for kdump other
> > than the normal expectation.
> > 
> > Can you check if this is also your case?
> 
> The question is to Paul,  also it would be always good to cc kexec mail
> list for kexec and kdump issues.

Looks like hardware iommu is used, maybe you do not enable SME?

Also replace maxcpus=1 with nr_cpus=1 can save some memory, can have a
try.