Messages in this thread | | | Date | Tue, 14 Jul 2015 14:45:59 -0600 | From | Jens Axboe <> | Subject | Re: [PATCH 3/3] block: by default, limit maximum discard size to 64MB |
| |
On 07/14/2015 02:44 PM, Mike Snitzer wrote: > On Tue, Jul 14 2015 at 2:48pm -0400, > Jens Axboe <axboe@fb.com> wrote: > >> Lots of devices exhibit very high latencies for big discards, hurting >> reads and writes. By default, limit the max discard we will build to >> 64MB. This value has shown good results across a number of devices. >> >> This will potentially hurt discard throughput, from a provisioning >> point of view (when the user does mkfs.xfs, for instance, and mkfs >> issues a full device discard). If that becomes an issue, we could >> have different behavior for provisioning vs runtime discards. >> >> Signed-off-by: Jens Axboe <axboe@fb.com> > > Christoph suggested you impose this default for the specific > drivers/devices that benefit. I'm not following why imposing a 64MB > default is the right thing to do for all devices.
I'd argue that's most of them... But the testing we did was on NVMe. I can limit it to NVMe, no big deal.
> If this goes in I know for sure I'll need to work around it in DM-thinp.
In any case, that's a good point, dm/md should not have their own lower restrictions.
-- Jens Axboe
| |