From: Vlastimil Babka > Sent: 15 December 2021 10:34 > > On 12/15/21 08:27, Christoph Hellwig wrote: > > On Wed, Dec 15, 2021 at 07:03:35AM +0000, Hyeonggon Yoo wrote: > >> I'm not sure that allocating from ZONE_DMA32 instead of ZONE_DMA > >> for kdump kernel is nice way to solve this problem. > > > > What is the problem with zones in kdump kernels? > > My understanding is that kdump kernel can only use physical memory that it > got reserved by the main kernel, and the main kernel will reserve some block > of memory that doesn't include any pages from ZONE_DMA (first 16MB of > physical memory or whatnot). ... Is there still any support for any of the very old hardware that could only support 24bit DMA? I think the AMD PCnet-ISA and PCnet-PCI ethernet (lance) were both 32bit masters. (I don't remember ever having to worry about physical addresses.) I'm sure I remember some old SCSI boards only being able to do 24bit DMA. But I can't remember which bus interface they were. Unlikely to be ISA because it has always been hard to get a motherboard DMA channel into 'cascade mode'. Might have been some EISA boards - anyone still use those? So we are left with early PCI boards. It really is worth looking at what actually needs it at all. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
