This series allows to selectively enable/disable polling for completions in the block layer [1] on a per-I/O basis. For this it resurrects the preadv2/pwritev2 syscalls that Milosz prepared a while ago (and which are much simpler now due to VFS changes that happened in the meantime). That approach also had a man page update prepared, which I will resubmit with the current flags once this series makes it in. Polling for block I/O is important to reduce the latency on flash and post-flash storage technologies. On the fastest NVMe controller I have access to it almost halves latencies from over 7 microseconds to about 4 microseonds. But it only is usesful if we actually care for the latency of this particular I/O, and generally is a waste if enabled for all I/O to a given device. This series uses the per-I/O flags in preadv2/pwritev2 to control this behavior. The alternative would be a new O_* flag set at open time or using fcntl, but this is still to corse-grained for some applications and we're starting to run out out of open flags. Note that there are plenty of other use cases for preadv2/pwritev2 as well, but I'd like to concentrate on this one for now. Example are: non-blocking reads (the original purpose), per-I/O O_SYNC, user space support for T10 DIF/DIX applications tags and probably some more. [1] only supported for NVMe at the moment. -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
