On 4/30/18 4:59 PM, Eric Sandeen wrote: > On 4/30/18 2:58 PM, Jens Axboe wrote: >> On 4/30/18 1:57 PM, Eric Sandeen wrote: >>> On 4/30/18 2:21 PM, Jens Axboe wrote: > > ... > >>> Ok, but I'm not sure how that precludes a block device tunable? You'd tune >>> it for your workload, right? >> >> What kind of tunable are you thinking of? Right now we have one tunable, >> which is the max discard size. Patch #1 actually helps make this do what >> it should for sync discards, instead of just building a bio chain and >> submitting that all at once. >> >>> Or is the concern that it could only be for the entire block device, and >>> perhaps different partitions have different workloads? >>> >>> Sorry, caveman filesystem guy doesn't completely understand block devices. >> >> I just don't know what you are trying to tune :-) > > I'm wondering if "make discards synchronous" couldn't just be a block device > tunable, rather than a filesystem mount option tunable. See e-mail I just sent out. With that, you get that tunable bundled with the discard_max_bytes tunable. If you leave it at the default, which is generally very high, then you get huge discards. If you tune it down, they become basically sync. I don't think we need a separate tunable for this. It's still per-caller, which is good enough for us. I don't want to make it more complicated until people show up with a valid use case that shows we need it strictly throttled per-device. -- Jens Axboe
