On 10/27/2017 07:29 AM, Vlastimil Babka wrote: > On 10/24/2017 09:41 AM, C.Wehrmeyer wrote: >> On 2017-10-23 20:02, Michal Hocko wrote: >>> On Mon 23-10-17 19:52:27, C.Wehrmeyer wrote: >>> [...] >> >> 1. Provide a flag to mmap, which might be something different from >> MAP_HUGETLB. After all your question revolved merely around properly >> aligned pages - we don't want to *force* the kernel to reserve >> hugepages, we just want it to provide the proper alignment in this case. >> That wouldn't be very transparent, but it would be the easiest route to >> go (and mmap already kind-of supports such a thing). > > Maybe just have mmap() detect that the requested size is a multiple of > huge page size, and then align it automatically? I.e. a heuristic that > should work in 99% of the cases? We already do this for DAX (see thp_get_unmapped_area). So, not much code to write. But could potentially fragment address spaces more. We could also check to determine if the system/process/mapping is even THP enabled before doing the alignment. I like the idea, but still am concerned about fragmentation. In addition, even though applications shouldn't care where new mappings are placed it would not surprise me that such a change will be noticeable to some. -- Mike Kravetz -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
