Am 11.09.19 um 17:08 schrieb Thomas Hellström (VMware): > On 9/11/19 4:06 PM, Koenig, Christian wrote: >> Am 11.09.19 um 12:10 schrieb Thomas Hellström (VMware): >> [SNIP] >>>>> The problem seen in TTM is that we want to be able to change the >>>>> vm_page_prot from the fault handler, but it's problematic since we >>>>> have the mmap_sem typically only in read mode. Hence the fake vma >>>>> hack. From what I can tell it's reasonably well-behaved, since >>>>> pte_modify() skips the bits TTM updates, so mprotect() and mremap() >>>>> works OK. I think split_huge_pmd may run into trouble, but we don't >>>>> support it (yet) with TTM. >>>> Ah! I actually ran into this while implementing huge page support for >>>> TTM and never figured out why that doesn't work. Dropped CPU huge page >>>> support because of this. >>> By incident, I got slightly sidetracked the other day and started >>> looking at this as well. Got to the point where I figured out all the >>> hairy alignment issues and actually got huge_fault() calls, but never >>> implemented the handler. I think that's definitely something worth >>> having. Not sure it will work for IO memory, though, (split_huge_pmd >>> will just skip non-page-backed memory) but if we only support >>> VM_SHARED (non COW) vmas there's no reason to split the huge pmds >>> anyway. Definitely something we should have IMO. >> Well our primary use case would be IO memory, cause system memory is >> only optionally allocate as huge page but we nearly always allocate VRAM >> in chunks of at least 2MB because we otherwise get a huge performance >> penalty. > > But that system memory option is on by default, right? In any case, a > request for a huge_fault > would probably need to check that there is actually an underlying > huge_page and otherwise fallback to ordinary faults. > > Another requirement would be for IO memory allocations to be > PMD_PAGE_SIZE aligned in the mappable aperture, to avoid fallbacks to > ordinary faults. Probably increasing fragmentation somewhat. (Seems > like pmd entries can only point to PMD_PAGE_SIZE aligned physical > addresses) Would that work for you? Yeah, we do it this way anyway. Regards, Christian. _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
