Dear Dave, Thank you for your replies. On 2019-08-13 04:54, Dave Young wrote: > On 08/13/19 at 10:46am, Dave Young wrote: >> On 08/13/19 at 10:43am, Dave Young wrote: >>> On 08/12/19 at 11:50am, 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) 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. As already replied <kexec@xxxxxxxxxxxxxxxxxxx> was CCed in my original message, but the list put it under moderation. > Looks like hardware iommu is used, maybe you do not enable SME? Do you mean AMD Secure Memory Encryption? I do not think, we use that. > Also replace maxcpus=1 with nr_cpus=1 can save some memory, can have a > try. Thank you for this suggestion. That fixed it indeed, and the reserved memory can stay at 256 MB. (The parameter names are a little unintuitive – I guess due to historical reasons. Kind regards, Paul [1]: https://www.kernel.org/doc/Documentation/admin-guide/kernel-parameters.txt
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