From: Jens Axboe <axboe@fb.com>
To: <linux-kernel@vger.kernel.org>
Cc: <snitzer@redhat.com>, <hch@lst.de>
Subject: [PATCH 0/3 v2] Configurable max discard size
Date: Tue, 14 Jul 2015 12:48:20 -0600 [thread overview]
Message-ID: <1436899703-31966-1-git-send-email-axboe@fb.com> (raw)
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.
Changes since v1:
- Keep separate sysfs files for hw and sw max discard values.
- Add patch 3, defaulting to 64MB discard sizes.
--
Jens Axboe
next reply other threads:[~2015-07-14 18:48 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-14 18:48 Jens Axboe [this message]
2015-07-14 18:48 ` [PATCH 1/3] block: have drivers use blk_queue_max_discard_sectors() Jens Axboe
2015-07-16 14:46 ` Jeff Moyer
2015-07-14 18:48 ` [PATCH 2/3] block: make /sys/block/<dev>/queue/discard_max_bytes writeable Jens Axboe
2015-07-16 15:07 ` Jeff Moyer
2015-07-16 15:11 ` Jens Axboe
2015-07-14 18:48 ` [PATCH 3/3] block: by default, limit maximum discard size to 64MB Jens Axboe
2015-07-14 20:44 ` Mike Snitzer
2015-07-14 20:45 ` Jens Axboe
2015-07-14 21:48 ` Jens Axboe
2015-07-15 11:46 ` Austin S Hemmelgarn
2015-07-15 15:30 ` Jens Axboe
2015-07-15 16:29 ` Mike Snitzer
2015-07-15 22:14 ` Jens Axboe
2015-08-05 13:34 ` Mike Snitzer
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