On 2018-03-10 10:01 AM, Christian König wrote: >> To accomodate those we need to >> create a "hole" inside the process address space. This patchset have >> a hack for that (patch 13 HACK FOR HMM AREA), it reserves a range of >> device file offset so that process can mmap this range with PROT_NONE >> to create a hole (process must make sure the hole is below 1 << 40). >> I feel un-easy of doing it this way but maybe it is ok with other >> folks. > > Well we have essentially the same problem with pre gfx9 AMD hardware. > Felix might have some advise how it was solved for HSA. For pre-gfx9 hardware we reserve address space in user mode using a big mmap PROT_NONE call at application start. Then we manage the address space in user mode and use MAP_FIXED to map buffers at specific addresses within the reserved range. The big address space reservation causes issues for some debugging tools (clang-sanitizer was mentioned to me), so with gfx9 we're going to get rid of this address space reservation. Regards, Felix
