On 09/02/2015 05:23 PM, Dave Hansen wrote: <> > 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. What tens-of-gigabytes mapping? I have yet to encounter an application that does that. Our tests show that usually the mmaps are small. I can send you a micro benchmark results of an mmap vs direct-io random write. Our code will jump over holes in the file BTW, but I'll ask to also run it with falloc that will make all blocks allocated. Give me a few days to collect this. I guess one optimization we should do is jump over holes and zero-extents. This will save the case of a mostly sparse very big file. Thanks Boaz -- 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>