linux-kernel - Re: [PATCH v6 05/11] block: remove split code in blkdev_issue_{discard,write

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Message-ID: <20151021153351.GA4984@redhat.com>
Date:	Wed, 21 Oct 2015 11:33:51 -0400
From:	Mike Snitzer <snitzer@...hat.com>
To:	Ming Lin <mlin@...nel.org>
Cc:	Jeff Moyer <jmoyer@...hat.com>,
	Christoph Hellwig <hch@...radead.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Jens Axboe <axboe@...nel.dk>,
	Kent Overstreet <kent.overstreet@...il.com>,
	Dongsu Park <dpark@...teo.net>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Ming Lin <ming.l@....samsung.com>,
	linux-nvme@...ts.infradead.org
Subject: Re: [PATCH v6 05/11] block: remove split code in
 blkdev_issue_{discard,write_same}

On Wed, Oct 21 2015 at 11:01am -0400,
Ming Lin <mlin@...nel.org> wrote:

> On Wed, 2015-10-21 at 09:39 -0400, Jeff Moyer wrote:
> > Christoph Hellwig <hch@...radead.org> writes:
> > 
> > > Jens, Ming:
> > >
> > > are you fine with the one liner change to get back to the old I/O
> > > pattern?  While it looks like the cards fault I'd like to avoid this
> > > annoying regression.
> > 
> > I'm not Jens or Ming, but your patch looks fine to me, though you'll
> > want to remove the MAX_BIO_SECTORS definition since it's now unused.
> > It's not clear to me why the limit was lowered in the first place.
> 
> UINT_MAX >> 9 is not power of 2 and it causes dm-thinp discard fails.
> 
> At the lengthy discussion:
> [PATCH v5 01/11] block: make generic_make_request handle arbitrarily sized bios
> We agreed to cap discard to 2G as an interim solution for 4.3 until the
> dm-thinp discard code is rewritten.

But did Jens ever commit that change to cap at 2G?  I don't recall
seeing it.

> Hi Mike,
> 
> Will the dm-thinp discard rewritten ready for 4.4?

No.  I'm not clear what needs changing in dm-thinp.  I'll have to
revisit the thread to refresh my memory.

BTW, DM thinp can easily handle discards that aren't a power-of-2 so
long as the requested discard is a factor of the thinp blocksize.
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