Messages in this thread | | | Date | Wed, 21 Aug 2002 06:43:46 +0200 | From | Mike Galbraith <> | Subject | RE: Alloc and lock down large amounts of memory |
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At 04:47 PM 8/20/2002 -0400, Richard B. Johnson wrote: >On Tue, 20 Aug 2002, Bhavana Nagendra wrote: > > > > > > > Curiosity: why do you want to do device DMA buffer > > > allocation from userland? > > > > I need 256M memory for a graphics operation. It's a requiremment, > > can't change it. There will be other reasonably sized allocs in kernel > > space, this is a special case that will be done from userland. As > > discussed earlier in this thread, there's no good way of alloc()ing > > and pinning that much in DMA memory space, is there? > > > > Gilad, I looked at mm/memory.c and map_user_kiobuf() lets me > > map user memory into kernel memory and pins it down. A scatter > > gatter mapping (say, pci_map_sg()) will create a seemingly > > contiguous buffer for DMA purposes. Does that sound right to you? > > > > Bhavana > >You have to cheat. You can tell the kernel that you only have, say >128 Meg of RAM.
Why not just use early allocation? (if he has eg a 16G box, chopping it down enough to get at 256M of DMA ram just ain't gonna work:)
-Mike
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