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From: "Martin K. Petersen" <martin.petersen@oracle.com>
To: "Theodore Ts'o" <tytso@mit.edu>
Cc: linux-fsdevel@vger.kernel.org, Jens Axboe <axboe@kernel.dk>
Subject: Re: [PATCH RFC] block: use discard if possible in blkdev_issue_discard()
Date: Fri, 14 Feb 2014 12:14:42 -0500	[thread overview]
Message-ID: <yq1ioshobul.fsf@sermon.lab.mkp.net> (raw)
In-Reply-To: <20140214043256.GA5145@thunk.org> (Theodore Ts'o's message of "Thu, 13 Feb 2014 23:32:56 -0500")

>>>>> "Ted" == Theodore Ts'o <tytso@mit.edu> writes:

Ted,

[issue_zeroout_or_write_same]

Ted> How do people think I should implement this functionality?  I see
Ted> three possible choices:

I did think about doing this when I originally implemented support for
WRITE SAME. However, one caveat is that there are corner cases where
devices that -- despite reporting that they return zeroed data after
TRIM -- will return non-zeroes. The issue being that TRIM is a hint and
there are no hard guarantees. Even if a device reports DRAT/RZAT.

So the reason I didn't end up adding a call like yours is that the
result is non-deterministic. The call would have to be "please zero this
block range but I don't *actually* rely on getting zeroes back". I don't
have a problem providing a function that does that as long as the
best-effort limitation is made crystal clear.

-- 
Martin K. Petersen	Oracle Linux Engineering

  parent reply	other threads:[~2014-02-14 17:14 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-02-14  4:32 [PATCH RFC] block: use discard if possible in blkdev_issue_discard() Theodore Ts'o
2014-02-14 13:05 ` Christoph Hellwig
2014-02-14 14:57   ` Theodore Ts'o
2014-02-14 17:14 ` Martin K. Petersen [this message]
2014-02-15  1:29   ` Theodore Ts'o
2014-02-17 16:44     ` Martin K. Petersen
2014-02-17 19:19       ` Theodore Ts'o
2014-02-18  1:31         ` Martin K. Petersen
2014-02-18  2:17           ` Theodore Ts'o
2014-02-18  3:44             ` Martin K. Petersen
2014-02-18  5:47               ` Theodore Ts'o
2014-02-19  2:20                 ` Martin K. Petersen
2014-02-17 16:41   ` Lukáš Czerner

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