>>>>> "Greg" == Greg Freemyer <greg.freemyer@xxxxxxxxx> writes: Greg> Is it also agreed by all that the current ext4 kernel Greg> implementation of calling discard is a poor solution for most Greg> hardware / block layers stacks / workloads and therefore is not Greg> worth retaining nor performing further benchmarks? Our discard implementation is meant to accommodate a wide range of devices. Just because some of the currently shipping low-end consumer SSDs implement TRIM poorly does not mean we're going to scrap what we have. We are not in the business of designing for the past. Especially not when the past can be handled by a shell script. For future devices TRIM/UNMAP is going to be an inherent part of the command set. And that's what our kernel support is aimed at. There are some deficiencies right now because the block layer was not built to handle what is essentially a hybrid between a filesystem and a blk_pc type request. I'm working on fixing that. Greg> I've not seen anyone arguing to keep the current kernel Greg> implementation and I for one accept the previously posted Greg> benchmarks that show it is not adding any value relative to the Greg> traditional non-discard case. For enterprise storage the cost of sending discards is limited to the overhead of sending the command. I.e. negligible. Eventually that's going to be the case for ATA devices as well. And let me just reiterate that Windows 7 does issue TRIM like we do (at runtime). And consequently Windows 7 will help weed out the crap SSD implementations from the market. That's already happening. There is also work underway to make TRIM a queueable command which would further alleviate the situation. Greg> Therefore benchmarks between the current hdparm/wiper.sh userspace Greg> implementation and a proposed new kernel implementation would be Greg> the most beneficial? I don't know what you mean by "new" kernel implementation. We're working on tweaking what we have so that we can split, merge, and coalesce requests. I'm also not sure why you're so hung up on benchmarks. The purpose of TRIM is to increase longevity of a flash-based device. For dumb devices there's currently a tradeoff - do you want speed or endurance? Once devices get smarter that tradeoff will disappear. -- Martin K. Petersen Oracle Linux Engineering -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
