On Thu, 2019-10-31 at 18:02 +0000, Catalin Marinas wrote: > On Thu, Oct 31, 2019 at 05:04:34PM +0100, Nicolas Saenz Julienne wrote: > > 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. > > The 'high' flag actually talks about crashkernel reserved above 4G which > is not really the case here. Since RPi4 is the odd one out, I'd rather > have the default crashkernel and CMA in the ZONE_DMA32 (current mainline > behaviour) and have the RPi4 use explicit size@offset parameters for > crashkernel and cma. Fair enough, I'll send a fix for this on Monday if it's OK with you.
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