linux-kernel - [PATCH 0/2] Configurable max discard size

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Message-ID: <1436886139-18673-1-git-send-email-axboe@fb.com>
Date:	Tue, 14 Jul 2015 09:02:17 -0600
From:	Jens Axboe <axboe@...com>
To:	<linux-kernel@...r.kernel.org>
CC:	<snitzer@...hat.com>, <hch@....de>
Subject: [PATCH 0/2] Configurable max discard size

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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