linux-kernel - Re: Crash kernel with 256 MB reserved memory runs into OOM condition

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Date:   Tue, 13 Aug 2019 10:43:17 +0800
From:   Dave Young <dyoung@...hat.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Paul Menzel <pmenzel@...gen.mpg.de>, linux-pci@...r.kernel.org,
        Jörg Rödel <joro@...tes.org>,
        "x86@...nel.org" <x86@...nel.org>, kexec@...ts.infradead.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        iommu@...ts.linux-foundation.org, kasong@...hat.com,
        lijiang@...hat.com, bhe@...hat.com,
        Donald Buczek <buczek@...gen.mpg.de>
Subject: Re: Crash kernel with 256 MB reserved memory runs into OOM condition

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?

Thanks
Dave