On 09/02/2015 03:27 AM, Boaz Harrosh wrote: >> > Yet you're ignoring the fact that flushing the entire range of the >> > relevant VMAs may not be very efficient. It may be a very >> > large mapping with only a few pages that need flushing from the >> > cache, but you still iterate the mappings flushing GB ranges from >> > the cache at a time. >> > > So actually you are wrong about this. We have a working system and as part > of our testing rig we do performance measurements, constantly. Our random > mmap 4k writes test preforms very well and is in par with the random-direct-write > implementation even though on every unmap, we do a VMA->start/end cl_flushing. > > The cl_flush operation is a no-op if the cacheline is not dirty and is a > memory bus storm with all the CLs that are dirty. So the only cost > is the iteration of vma->start-to-vma->end i+=64 I'd be curious what the cost is in practice. Do you have any actual numbers of the cost of doing it this way? Even if the instruction is a "noop", I'd really expect the overhead to really add up for a tens-of-gigabytes mapping, no matter how much the CPU optimizes it. -- 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>