On Thu, 2019-10-31 at 15:51 +0000, Catalin Marinas wrote: > (sorry, I've been away last week and only now caught up with emails) > > On Tue, Oct 22, 2019 at 01:23:32PM +0200, Nicolas Saenz Julienne wrote: > > On Mon, 2019-10-21 at 16:36 -0400, Qian Cai wrote: > > > I managed to get more information here, > > > > > > [ 0.000000] cma: dma_contiguous_reserve(limit c0000000) > > > [ 0.000000] cma: dma_contiguous_reserve: reserving 64 MiB for global > > > area > > > [ 0.000000] cma: cma_declare_contiguous(size 0x0000000004000000, base > > > 0x0000000000000000, limit 0x00000000c0000000 alignment 0x0000000000000000) > > > [ 0.000000] cma: Failed to reserve 512 MiB > > > > > > Full dmesg: > > > > > > https://cailca.github.io/files/dmesg.txt > > > > OK I got it, reproduced it too. > > > > Here are the relevant logs: > > > > [ 0.000000] DMA [mem 0x00000000802f0000-0x00000000bfffffff] > > [ 0.000000] DMA32 [mem 0x00000000c0000000-0x00000000ffffffff] > > [ 0.000000] Normal [mem 0x0000000100000000-0x00000097fcffffff] > > > > As you can see ZONE_DMA spans from 0x00000000802f0000-0x00000000bfffffff > > which > > is slightly smaller than 1GB. > > > > [ 0.000000] crashkernel reserved: 0x000000009fe00000 - > > 0x00000000bfe00000 (512 MB) > > > > Here crashkernel reserved 512M in ZONE_DMA. > > > > [ 0.000000] cma: Failed to reserve 512 MiB > > > > CMA tried to allocate 512M in ZONE_DMA which fails as there is no enough > > space. > > Makes sense. > > > > A fix could be moving crashkernel reservations after CMA and then if unable > > to > > fit in ZONE_DMA try ZONE_DMA32 before bailing out. Maybe it's a little over > > the > > top, yet although most devices will be fine with ZONE_DMA32, the RPi4 needs > > crashkernel to be reserved in ZONE_DMA. > > Does RPi4 need CMA in ZONE_DMA? If not, I'd rather reserve the CMA from > ZONE_DMA32. Yes, CMA is imperatively to be reserved in ZONE_DMA. > Even if you moved the crash kernel, someone else might complain that > they had 2GB of CMA and it no longer works. I have yet to look into it, but I've been told that on x86/x64 they have a 'high' flag to be set alongside with crashkernel that forces the allocation into ZONE_DMA32. We could mimic this behavior for big servers that don't depend on ZONE_DMA but need to reserve big chunks of memory. Regards, Nicolas
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