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From: Jens Axboe <axboe@fb.com>
To: Mike Snitzer <snitzer@redhat.com>
Cc: <linux-kernel@vger.kernel.org>, <hch@lst.de>
Subject: Re: [PATCH 3/3] block: by default, limit maximum discard size to 64MB
Date: Tue, 14 Jul 2015 15:48:15 -0600	[thread overview]
Message-ID: <55A5839F.8060608@fb.com> (raw)
In-Reply-To: <55A57507.1030302@fb.com>

On 07/14/2015 02:45 PM, Jens Axboe wrote:
> 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.

Oh, and LSI flash too, so not just NVMe.

-- 
Jens Axboe


  reply	other threads:[~2015-07-14 21:48 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-07-14 18:48 [PATCH 0/3 v2] Configurable max discard size Jens Axboe
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 [this message]
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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