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To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Theodore Ts'o" <tytso@mit.edu>,
        "Darrick J. Wong" <darrick.wong@oracle.com>,
        Jens Axboe <axboe@kernel.dk>, Christoph Hellwig <hch@infradead.org>,
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Subject: Re: [PATCH 2/2] block: create ioctl to discard-or-zeroout a range of blocks
From: "Martin K. Petersen" <martin.petersen@oracle.com>
Organization: Oracle Corporation
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Date: Thu, 03 Mar 2016 13:14:12 -0500
In-Reply-To: <CA+55aFwPA1X8XGTdVZmP5uzkWMwj+X=bjkGVcEkZDme+qskrzQ@mail.gmail.com>
	(Linus Torvalds's message of "Thu, 3 Mar 2016 09:55:38 -0800")
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>>>>> "Linus" == Linus Torvalds <torvalds@linux-foundation.org> writes:

Linus> On Thu, Mar 3, 2016 at 9:02 AM, Theodore Ts'o <tytso@mit.edu> wrote:
>> 
>> There is a massive bug in the SATA specs about trim, which is that it
>> is considered advisory.  So the storage device can throw it away
>> whenever it feels like it.  (In practice, when it's too busy doing
>> other things).

Linus> Ugh.

SCSI UNMAP provides similar semantics :(

Linus> But that essentially says that we shouldn't expose this interface
Linus> at all (unless we trust our white-lists - I'm sure they are
Linus> getting better, but if nobody has ever really _relied_ on the
Linus> zeroing behavior of trim, then I guess there could be tons of
Linus> bugs lurking).

We started out with the blacklist approach and it blew up. So now we're
down to a whitelist of drives that have been sanctioned by their
manufacturers to do the right thing.

Occasionally a new SSD model messes things up but we haven't updated it
since last summer. The drive vendors are much better at testing using
Linux than they used to be.

-- 
Martin K. Petersen	Oracle Linux Engineering