linux-ext4 - Re: [PATCH] e2fsck: Discard free data and inode blocks.

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Message-ID: <4CC1D6A8.6080000@redhat.com>
Date:	Fri, 22 Oct 2010 13:23:36 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	"Martin K. Petersen" <martin.petersen@...cle.com>
CC:	Ric Wheeler <ricwheeler@...il.com>,
	Lukas Czerner <lczerner@...hat.com>,
	Andreas Dilger <adilger.kernel@...ger.ca>,
	linux-ext4@...r.kernel.org, tytso@....edu
Subject: Re: [PATCH] e2fsck: Discard free data and inode blocks.

Martin K. Petersen wrote:
>>>>>> "Ric" == Ric Wheeler <ricwheeler@...il.com> writes:
> 
>>> so we're not depending on it zeroing blocks, we're just depending on
>>> it advertising correctly whether or not it -does- zero.
> 
> If the relevant bits are set (ATA: DRAT and RZAT, SCSI: TPRZ) we'll set
> the bdev's discard_zeroes_data flag.
> 
> [root@...t ~]# lsscsi | grep SSD | awk '{ print $7 }'
> /dev/sde
> [root@...t ~]# grep . /sys/block/sde/queue/discard_zeroes_data 
> 1
> 
> The relevant ioctl is BLKDISCARDZEROES.

which is what that patch I pointed to uses, BTW...

I really think it's on firm footing here, we're not assuming
discard == zeroed data, we are checking whether the drive
reports exactly that behavior ...

-Eric
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