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Subject: Re: Crash kernel with 256 MB reserved memory runs into OOM condition
To:     Michal Hocko <mhocko@kernel.org>
Cc:     =?UTF-8?B?SsO2cmcgUsO2ZGVs?= <joro@8bytes.org>,
        iommu@lists.linux-foundation.org, linux-pci@vger.kernel.org,
        "x86@kernel.org" <x86@kernel.org>, kexec@lists.infradead.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Donald Buczek <buczek@molgen.mpg.de>
References: <d65e4a42-1962-78c6-1b5a-65cb70529d62@molgen.mpg.de>
 <20190812095029.GE5117@dhcp22.suse.cz>
From:   Paul Menzel <pmenzel@molgen.mpg.de>
Message-ID: <f22573e6-320e-21a1-be1e-c854d8090df8@molgen.mpg.de>
Date:   Mon, 12 Aug 2019 11:59:03 +0200
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Dear Michal,


On 12.08.19 11:50, Michal Hocko wrote:
> On Mon 12-08-19 11:42:33, Paul Menzel wrote:

>> On a Dell PowerEdge R7425 with two AMD EPYC 7601 (total 128 threads) a=
nd
>> 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.
>=20
> You will need more memory to reserve for the crash kernel because ...
>=20
>> [    4.548703] Node 0 DMA free:484kB min:4kB low:4kB high:4kB active_a=
non:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB unevictable:0=
kB 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:214=
0kB active_anon:0kB inactive_anon:0kB active_file:0kB inactive_file:0kB u=
nevictable:15720kB writepending:0kB present:261560kB managed:133752kB mlo=
cked:0kB kernel_stack:2496kB pagetables:0kB bounce:0kB free_pcp:212kB loc=
al_pcp:212kB free_cma:0kB
>=20
> ... 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).
>=20
> [...]
>> [    4.923156] Out of memory and no killable processes...
>=20
> and there is no task existing to be killed so we go and panic.

Yeah, we figured that.

What we wonder is, how 256 MB are not enough for booting, and what
hardware properties cause it to be too small. In the overview I just
see a 60 MB allocation.

    [    4.857565] kmalloc-2048           59164KB      59164KB


Kind regards,

Paul


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