Comment # 2 on bug 1224805 from Jiri Bohac

Kdump seems to be a random victim of a low memory situation.
The kdump init script calls the kexec binary which, in this case, does a XEN 
hypercall via xen_pv_evtchn_do_upcall() to load the kexec kernel/initrd into
XEN.
The allocation fails during xen_pv_evtchn_do_upcall().

This is an order 4 allocation (64 kB) and there is no such block available in
the DMA32 zone:

2024-05-17T03:32:50.909346+02:00 unreal6 kernel: [300981.301042][T22543] Node 0
DMA: 40*4kB (UME) 29*8kB (UME) 36*16kB (UE) 14*32kB (UME) 4*64kB (UME) 4*128kB
(UE) 3*256kB (U) 1*512kB (U) 0*1024kB 0*2048kB 0*4096kB = 3464kB
2024-05-17T03:32:50.909351+02:00 unreal6 kernel: [300981.448605][T22543] Node 0
DMA32: 7108*4kB (UMEH) 1421*8kB (UMEH) 50*16kB (UMH) 3*32kB (H) 0*64kB 0*128kB
0*256kB 0*512kB 0*1024kB 0*2048kB 0*4096kB = 40696kB

Adding Vlastimil to CC - could you have a look why the required memory could
not be reclaimed? The system only has 1 GB total memory but some free swap
remains.