Re: [PATCHSET 0/2] sync discard

Jens Axboe
2018-05-02T14:19:43Z

On 5/2/18 6:45 AM, Christoph Hellwig wrote:
> On Mon, Apr 30, 2018 at 09:32:50AM -0600, Jens Axboe wrote:
>> We recently had a pretty severe perf regression with the XFS async
>> discard. This small series add a SYNC issue discard flag, and also
>> limits the chain size for sync discards. Patch 2 adds support for
>> reverting XFS back to doign sync discards.
>
> Please explain the hardware and workload that you see this with.
> Also given that it is a hardware limitation a quirk limiting the
> size of discard requests and/or number of outstanding discards
> would be more useful than falling back to a broken mode of issueing
> block commands.

Honestly, from what I've seen in production, I can whitelist one
device and that one is no longer being produced. The rest is crap
in terms of latency impacting trim. A quirk or whitelist/blacklist
isn't going to be of any help.

--
Jens Axboe