Re: [PATCH 1/4] block: Allow devices to indicate whether discarded blocks are zeroed

From: Christoph Hellwig <hch@infradead.org>
To: Ric Wheeler <rwheeler@redhat.com>
Cc: Greg Freemyer <greg.freemyer@gmail.com>, Mark Lord <liml@rtr.ca>,
	Matthew Wilcox <matthew@wil.cx>,
	Christoph Hellwig <hch@infradead.org>,
	"Martin K. Petersen" <martin.petersen@oracle.com>,
	jens.axboe@oracle.com, james.bottomley@hansenpartnership.com,
	willy@wil.cx, jgarzik@pobox.com, sandeen@redhat.com,
	linux-ide@vger.kernel.org, linux-scsi@vger.kernel.org
Subject: Re: [PATCH 1/4] block: Allow devices to indicate whether discarded blocks are zeroed
Date: Mon, 23 Nov 2009 12:03:25 -0500	[thread overview]
Message-ID: <20091123170325.GA23217@infradead.org> (raw)
In-Reply-To: <4B0AC038.6050606@redhat.com>

On Mon, Nov 23, 2009 at 12:02:48PM -0500, Ric Wheeler wrote:
> I agree - the discard of the whole device is a good idea.
>
> I just want to make clear that "discard block X; write block X with 
> zeroed data" undoes the discard in general :-)

We can skip the writing of zeroes if we know the device returns zeroed
blocks after a trim.  Martin's patch exports that information to
userspace, and once we have a nice enough interface (e.g. blkid or an
ioctl) we can actually use it in mkfs to optimize the writing of zeroes
away.  Raw growling in sysfs is a bit too nasty to add it to mkfs for
those few blocks IMHO.