A sentence or two got chopped out during an editing pass. Let me try that again so it's a bit clearer what I was trying to say.... Sure, but if the block device supports WRITE_SAME or persistent discard, then presumably fallocate() should do this automatically all the time, and not require a flag to request this behavior. The only reason why you might not is if the WRITE_SAME is more costly. That is when a seek plus writing 1MB does take more time than the amount of disk time fraction that it consumes if you compare it to a seek plus writing 4k or 32k. Ext4 currently uses a threshold of 32k for this break point (below that, we will use sb_issue_zeroout; above that, we will break apart an uninitialized extent when writing into a preallocated region). It may be that 32k is too low, especailly for certain types of devices (i.e., SSD's versus RAID 5, where it should be aligned on a RAID strip, etc.). More of an issue might be that there will be some disagreement about whether people want to the system to automatically tune for average throughput vs 99.9 percentile latency. Regardless, this is actually something which I think the file system should try to do automatically if at all possible, via some kind of auto-tuning hueristic, instead of using an explicit fallocate(2) flag. (See, I don't propose using a new fallocate flag for everything. :-) - Ted -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html