linux-ext4 - Re: [PATCH 2/2] Add batched discard support for ext4.

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Date:	Sat, 24 Apr 2010 09:43:31 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	Greg Freemyer <greg.freemyer@...il.com>
CC:	Ric Wheeler <rwheeler@...hat.com>,
	Lukas Czerner <lczerner@...hat.com>,
	Jeff Moyer <jmoyer@...hat.com>,
	Mark Lord <kernel@...savvy.com>, linux-ext4@...r.kernel.org,
	Edward Shishkin <eshishki@...hat.com>,
	Eric Sandeen <esandeen@...hat.com>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH 2/2] Add batched discard support for ext4.

Greg Freemyer wrote:
> On Sat, Apr 24, 2010 at 9:48 AM, Ric Wheeler <rwheeler@...hat.com> wrote:
>> On 04/24/2010 09:24 AM, Greg Freemyer wrote:

...

>>> I know I've been arguing against this patch for the single SSD case
>>> and I still think that use case should be handled by userspace as
>>> hdparm/wiper.sh currently does.  In particular for those extreme
>>> scenarios with JBOD SSDs, the user space solution wins because it
>>> knows how to optimize the trim calls via vectorized ranges in the
>>> payload.
>>>
>> I think that you have missed the broader point. This is not on by default,
>> so you can mount without discard and use whatever user space utility you
>> like at your discretion.
>>
>> ric
> 
> Ric,
> 
> I was trying to say the design should be driven by the large discard
> range use case, not the potentially pathological small discard range
> use case that would only benefit SSDs.
> 
> Greg

Bear in mind that this patch makes the discard range requests substantially
-larger- than what mount -o discard does on ext4 today, in fact that was
a main goal.

If the kernel could assemble vectors of ranges and pass them down, I think it
could be extended to use that as well.

-Eric
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