Re: [PATCH v6 05/11] block: remove split code in blkdev_issue_{discard,write_same}

From	Mike Snitzer <snitzer@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v6 05/11] block: remove split code in blkdev_issue_{discard,write_same}
Date	2015-10-21 17:40 +0200
Message-ID	<qm3EC-7ex-33@gated-at.bofh.it> (permalink)
References	(2 earlier) <qj6pk-5Fz-15@gated-at.bofh.it> <qjbS2-5fW-23@gated-at.bofh.it> <qlW0q-4sL-3@gated-at.bofh.it> <qm1Wb-4CG-35@gated-at.bofh.it> <qm3bB-6Fw-39@gated-at.bofh.it>
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On Wed, Oct 21 2015 at 11:01am -0400,
Ming Lin <mlin@kernel.org> wrote:

> On Wed, 2015-10-21 at 09:39 -0400, Jeff Moyer wrote:
> > Christoph Hellwig <hch@infradead.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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Thread

Re: [PATCH v6 05/11] block: remove split code in  blkdev_issue_{discard,write_same} Christoph Hellwig <hch@infradead.org> - 2015-10-21 09:30 +0200
  Re: [PATCH v6 05/11] block: remove split code in blkdev_issue_{discard,write_same} Jeff Moyer <jmoyer@redhat.com> - 2015-10-21 15:50 +0200
    Re: [PATCH v6 05/11] block: remove split code in  blkdev_issue_{discard,write_same} Ming Lin <mlin@kernel.org> - 2015-10-21 17:10 +0200
      Re: [PATCH v6 05/11] block: remove split code in  blkdev_issue_{discard,write_same} Mike Snitzer <snitzer@redhat.com> - 2015-10-21 17:40 +0200
        Re: [PATCH v6 05/11] block: remove split code in  blkdev_issue_{discard,write_same} Ming Lin <mlin@kernel.org> - 2015-10-21 19:20 +0200

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