Hi, Most drivers use UINT_MAX (or some variant thereof) for max discard size, since they don't have a real limit for a non-data transferring command. This is fine from a throughput point of view, but for a lot of devices (all?), it truly sucks on latency. We've seen cases of hundreds of msec in latencies for reads/writes when deleting files on an fs with discard enabled. For the problematic devices that we have tested, artificially limiting the size of the discards issued brings it down to a more manageable 1-2ms max latencies.
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