linux-kernel - Re: [PATCH 2/2] block: create ioctl to discard-or-zeroout a range of blocks

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Date:	Thu, 03 Mar 2016 13:14:12 -0500
From:	"Martin K. Petersen" <martin.petersen@...cle.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"Theodore Ts'o" <tytso@....edu>,
	"Darrick J. Wong" <darrick.wong@...cle.com>,
	Jens Axboe <axboe@...nel.dk>,
	Christoph Hellwig <hch@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Linux API <linux-api@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	shane.seymour@....com, Bruce Fields <bfields@...ldses.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	Jeff Layton <jlayton@...chiereds.net>
Subject: Re: [PATCH 2/2] block: create ioctl to discard-or-zeroout a range of blocks

>>>>> "Linus" == Linus Torvalds <torvalds@...ux-foundation.org> writes:

Linus> On Thu, Mar 3, 2016 at 9:02 AM, Theodore Ts'o <tytso@....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