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

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

[Christoph Hellwig]

On Wed, Aug 12, 2015@12:07:15AM -0700, Ming Lin wrote:
> From: Ming Lin <ming.l at ssi.samsung.com>
> 
> The split code in blkdev_issue_{discard,write_same} can go away
> now that any driver that cares does the split. We have to make
> sure bio size doesn't overflow.
> 
> For discard, we set max discard sectors to (1<<31)>>9 to ensure
> it doesn't overflow bi_size and hopefully it is of the proper
> granularity as long as the granularity is a power of two.

This ends up breaking discard on NVMe devices for a me.  An mkfs.xfs
which does a discard of the whole device now hangs the system.
Something in here makes it send discard command that the device doesn't
like and the aborts don't seem to help either, although that might be
an issue with the abort handling in the driver.

Just a heads up for now, once I get a bit more time I'll try to collect
a blktrace to figure out how the commands sent to the driver look
different before and after the patch.

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

[Ming Lin]

On Tue, Oct 13, 2015@4:50 AM, Christoph Hellwig <hch@infradead.org> wrote:
> On Wed, Aug 12, 2015@12:07:15AM -0700, Ming Lin wrote:
>> From: Ming Lin <ming.l at ssi.samsung.com>
>>
>> The split code in blkdev_issue_{discard,write_same} can go away
>> now that any driver that cares does the split. We have to make
>> sure bio size doesn't overflow.
>>
>> For discard, we set max discard sectors to (1<<31)>>9 to ensure
>> it doesn't overflow bi_size and hopefully it is of the proper
>> granularity as long as the granularity is a power of two.
>
> This ends up breaking discard on NVMe devices for a me.  An mkfs.xfs
> which does a discard of the whole device now hangs the system.
> Something in here makes it send discard command that the device doesn't
> like and the aborts don't seem to help either, although that might be
> an issue with the abort handling in the driver.
>
> Just a heads up for now, once I get a bit more time I'll try to collect
> a blktrace to figure out how the commands sent to the driver look
> different before and after the patch.

I just did a quick test with a Samsung 900G NVMe device.
mkfs.xfs is OK on 4.3-rc5.

What's your device model? I may find a similar one to try.

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

[Christoph Hellwig]

On Tue, Oct 13, 2015@10:44:11AM -0700, Ming Lin wrote:
> I just did a quick test with a Samsung 900G NVMe device.
> mkfs.xfs is OK on 4.3-rc5.
> 
> What's your device model? I may find a similar one to try.

This is a HGST Ultrastar SN100

Analsys and tentativ fix below:

blktrace for before the commit:

259,0    1        2     0.000002543  2394  G   D 0 + 8388607 [mkfs.xfs]
259,0    1        3     0.000008230  2394  I   D 0 + 8388607 [mkfs.xfs]
259,0    1        4     0.000031090   207  D   D 0 + 8388607 [kworker/1:1H]
259,0    1        5     0.000044869  2394  Q   D 8388607 + 8388607 [mkfs.xfs]
259,0    1        6     0.000045992  2394  G   D 8388607 + 8388607 [mkfs.xfs]
259,0    1        7     0.000049559  2394  I   D 8388607 + 8388607 [mkfs.xfs]
259,0    1        8     0.000061551   207  D   D 8388607 + 8388607 [kworker/1:1H]

.. and so on.

blktrace with the commit:

259,0    2        1     0.000000000  1228  Q   D 0 + 4194304 [mkfs.xfs]
259,0    2        2     0.000002543  1228  G   D 0 + 4194304 [mkfs.xfs]
259,0    2        3     0.000010080  1228  I   D 0 + 4194304 [mkfs.xfs]
259,0    2        4     0.000082187   267  D   D 0 + 4194304 [kworker/2:1H]
259,0    2        5     0.000224869  1228  Q   D 4194304 + 4194304 [mkfs.xfs]
259,0    2        6     0.000225835  1228  G   D 4194304 + 4194304 [mkfs.xfs]
259,0    2        7     0.000229457  1228  I   D 4194304 + 4194304 [mkfs.xfs]
259,0    2        8     0.000238507   267  D   D 4194304 + 4194304 [kworker/2:1H]

So discards are smaller, but better aligned.  Now if I tweak a single
line in blk-lib.c to be able to use all of bi_size I get the old I/O
pattern back and everything works fine again:

diff --git a/block/blk-lib.c b/block/blk-lib.c
index bd40292..65b61dc 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -82,7 +82,7 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
 			break;
 		}
 
-		req_sects = min_t(sector_t, nr_sects, MAX_BIO_SECTORS);
+		req_sects = min_t(sector_t, nr_sects, UINT_MAX >> 9);
 		end_sect = sector + req_sects;
 
 		bio->bi_iter.bi_sector = sector;

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

[Keith Busch]

On Wed, 14 Oct 2015, Christoph Hellwig wrote:
> Analsys and tentativ fix below:
>
> blktrace for before the commit:
>
> 259,0    1        2     0.000002543  2394  G   D 0 + 8388607 [mkfs.xfs]
> 259,0    1        3     0.000008230  2394  I   D 0 + 8388607 [mkfs.xfs]
> 259,0    1        4     0.000031090   207  D   D 0 + 8388607 [kworker/1:1H]
> 259,0    1        5     0.000044869  2394  Q   D 8388607 + 8388607 [mkfs.xfs]
> 259,0    1        6     0.000045992  2394  G   D 8388607 + 8388607 [mkfs.xfs]
> 259,0    1        7     0.000049559  2394  I   D 8388607 + 8388607 [mkfs.xfs]
> 259,0    1        8     0.000061551   207  D   D 8388607 + 8388607 [kworker/1:1H]
>
> .. and so on.
>
> blktrace with the commit:
>
> 259,0    2        1     0.000000000  1228  Q   D 0 + 4194304 [mkfs.xfs]
> 259,0    2        2     0.000002543  1228  G   D 0 + 4194304 [mkfs.xfs]
> 259,0    2        3     0.000010080  1228  I   D 0 + 4194304 [mkfs.xfs]
> 259,0    2        4     0.000082187   267  D   D 0 + 4194304 [kworker/2:1H]
> 259,0    2        5     0.000224869  1228  Q   D 4194304 + 4194304 [mkfs.xfs]
> 259,0    2        6     0.000225835  1228  G   D 4194304 + 4194304 [mkfs.xfs]
> 259,0    2        7     0.000229457  1228  I   D 4194304 + 4194304 [mkfs.xfs]
> 259,0    2        8     0.000238507   267  D   D 4194304 + 4194304 [kworker/2:1H]
>
> So discards are smaller, but better aligned.  Now if I tweak a single
> line in blk-lib.c to be able to use all of bi_size I get the old I/O
> pattern back and everything works fine again:

I see why the proposal is an improvement, but I don't understand why the
current situation results in a hang. Are we missing some kind of error
recovery in the driver?

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

[Christoph Hellwig]

On Wed, Oct 14, 2015@04:38:50PM +0000, Keith Busch wrote:
> I see why the proposal is an improvement, but I don't understand why the
> current situation results in a hang. Are we missing some kind of error
> recovery in the driver?

The driver tries to abort the commands and eventually gets into a death
spiral.  I'm still trying to understand what exactly is going on.

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

[Christoph Hellwig]

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.

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

[Jeff Moyer]

Christoph Hellwig <hch at 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.

You can add my Reviewed-by: Jeff Moyer <jmoyer at redhat.com> if you resend
the patch.

-Jeff

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

[Ming Lin]

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

Hi Mike,

Will the dm-thinp discard rewritten ready for 4.4?

Thanks,
Ming

> 
> You can add my Reviewed-by: Jeff Moyer <jmoyer at redhat.com> if you resend
> the patch.
> 
> -Jeff

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

[Mike Snitzer]

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

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

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

[Mike Snitzer]

On Wed, Oct 14 2015 at  9:27am -0400,
Christoph Hellwig <hch@infradead.org> wrote:

> On Tue, Oct 13, 2015@10:44:11AM -0700, Ming Lin wrote:
> > I just did a quick test with a Samsung 900G NVMe device.
> > mkfs.xfs is OK on 4.3-rc5.
> > 
> > What's your device model? I may find a similar one to try.
> 
> This is a HGST Ultrastar SN100
> 
> Analsys and tentativ fix below:
> 
> blktrace for before the commit:
> 
> 259,0    1        2     0.000002543  2394  G   D 0 + 8388607 [mkfs.xfs]
> 259,0    1        3     0.000008230  2394  I   D 0 + 8388607 [mkfs.xfs]
> 259,0    1        4     0.000031090   207  D   D 0 + 8388607 [kworker/1:1H]
> 259,0    1        5     0.000044869  2394  Q   D 8388607 + 8388607 [mkfs.xfs]
> 259,0    1        6     0.000045992  2394  G   D 8388607 + 8388607 [mkfs.xfs]
> 259,0    1        7     0.000049559  2394  I   D 8388607 + 8388607 [mkfs.xfs]
> 259,0    1        8     0.000061551   207  D   D 8388607 + 8388607 [kworker/1:1H]
> 
> .. and so on.
> 
> blktrace with the commit:
> 
> 259,0    2        1     0.000000000  1228  Q   D 0 + 4194304 [mkfs.xfs]
> 259,0    2        2     0.000002543  1228  G   D 0 + 4194304 [mkfs.xfs]
> 259,0    2        3     0.000010080  1228  I   D 0 + 4194304 [mkfs.xfs]
> 259,0    2        4     0.000082187   267  D   D 0 + 4194304 [kworker/2:1H]
> 259,0    2        5     0.000224869  1228  Q   D 4194304 + 4194304 [mkfs.xfs]
> 259,0    2        6     0.000225835  1228  G   D 4194304 + 4194304 [mkfs.xfs]
> 259,0    2        7     0.000229457  1228  I   D 4194304 + 4194304 [mkfs.xfs]
> 259,0    2        8     0.000238507   267  D   D 4194304 + 4194304 [kworker/2:1H]
> 
> So discards are smaller, but better aligned.  Now if I tweak a single
> line in blk-lib.c to be able to use all of bi_size I get the old I/O
> pattern back and everything works fine again:
> 
> diff --git a/block/blk-lib.c b/block/blk-lib.c
> index bd40292..65b61dc 100644
> --- a/block/blk-lib.c
> +++ b/block/blk-lib.c
> @@ -82,7 +82,7 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
>  			break;
>  		}
>  
> -		req_sects = min_t(sector_t, nr_sects, MAX_BIO_SECTORS);
> +		req_sects = min_t(sector_t, nr_sects, UINT_MAX >> 9);
>  		end_sect = sector + req_sects;
>  
>  		bio->bi_iter.bi_sector = sector;

Can we change UINT_MAX >> 9 to rounddown to the first factor of
minimum_io_size?

That should work for all devices and for dm-thinp (and dm-cache) in
particular will ensure that all discards that are issued will be a
multiple of the underlying device's blocksize.

Mike

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

[Mike Snitzer]

On Wed, Oct 21 2015 at 12:02pm -0400,
Mike Snitzer <snitzer@redhat.com> wrote:

> On Wed, Oct 14 2015 at  9:27am -0400,
> Christoph Hellwig <hch@infradead.org> wrote:
> 
> > On Tue, Oct 13, 2015@10:44:11AM -0700, Ming Lin wrote:
> > > I just did a quick test with a Samsung 900G NVMe device.
> > > mkfs.xfs is OK on 4.3-rc5.
> > > 
> > > What's your device model? I may find a similar one to try.
> > 
> > This is a HGST Ultrastar SN100
> > 
> > Analsys and tentativ fix below:
> > 
> > blktrace for before the commit:
> > 
> > 259,0    1        2     0.000002543  2394  G   D 0 + 8388607 [mkfs.xfs]
> > 259,0    1        3     0.000008230  2394  I   D 0 + 8388607 [mkfs.xfs]
> > 259,0    1        4     0.000031090   207  D   D 0 + 8388607 [kworker/1:1H]
> > 259,0    1        5     0.000044869  2394  Q   D 8388607 + 8388607 [mkfs.xfs]
> > 259,0    1        6     0.000045992  2394  G   D 8388607 + 8388607 [mkfs.xfs]
> > 259,0    1        7     0.000049559  2394  I   D 8388607 + 8388607 [mkfs.xfs]
> > 259,0    1        8     0.000061551   207  D   D 8388607 + 8388607 [kworker/1:1H]
> > 
> > .. and so on.
> > 
> > blktrace with the commit:
> > 
> > 259,0    2        1     0.000000000  1228  Q   D 0 + 4194304 [mkfs.xfs]
> > 259,0    2        2     0.000002543  1228  G   D 0 + 4194304 [mkfs.xfs]
> > 259,0    2        3     0.000010080  1228  I   D 0 + 4194304 [mkfs.xfs]
> > 259,0    2        4     0.000082187   267  D   D 0 + 4194304 [kworker/2:1H]
> > 259,0    2        5     0.000224869  1228  Q   D 4194304 + 4194304 [mkfs.xfs]
> > 259,0    2        6     0.000225835  1228  G   D 4194304 + 4194304 [mkfs.xfs]
> > 259,0    2        7     0.000229457  1228  I   D 4194304 + 4194304 [mkfs.xfs]
> > 259,0    2        8     0.000238507   267  D   D 4194304 + 4194304 [kworker/2:1H]
> > 
> > So discards are smaller, but better aligned.  Now if I tweak a single
> > line in blk-lib.c to be able to use all of bi_size I get the old I/O
> > pattern back and everything works fine again:
> > 
> > diff --git a/block/blk-lib.c b/block/blk-lib.c
> > index bd40292..65b61dc 100644
> > --- a/block/blk-lib.c
> > +++ b/block/blk-lib.c
> > @@ -82,7 +82,7 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
> >  			break;
> >  		}
> >  
> > -		req_sects = min_t(sector_t, nr_sects, MAX_BIO_SECTORS);
> > +		req_sects = min_t(sector_t, nr_sects, UINT_MAX >> 9);
> >  		end_sect = sector + req_sects;
> >  
> >  		bio->bi_iter.bi_sector = sector;
> 
> Can we change UINT_MAX >> 9 to rounddown to the first factor of
> minimum_io_size?
> 
> That should work for all devices and for dm-thinp (and dm-cache) in
> particular will ensure that all discards that are issued will be a
> multiple of the underlying device's blocksize.

Jeff Moyer pointed out having req_sects be a factor of
discard_granularity makes more sense.  And I agree.  Same difference in
the end (since dm-thinp sets discard_granularity to the thinp
blocksize).

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

[Martin K. Petersen]

>>>>> "Mike" == Mike Snitzer <snitzer at redhat.com> writes:

>> That should work for all devices and for dm-thinp (and dm-cache) in
>> particular will ensure that all discards that are issued will be a
>> multiple of the underlying device's blocksize.

Mike> Jeff Moyer pointed out having req_sects be a factor of
Mike> discard_granularity makes more sense.

Absolutely!

-- 
Martin K. Petersen	Oracle Linux Engineering

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

[Ming Lin]

On Wed, 2015-10-21@11:33 -0400, Mike Snitzer wrote:
> On Wed, Oct 21 2015 at 11:01am -0400,
> Ming Lin <mlin@kernel.org> wrote:
> 
> > On Wed, 2015-10-21@09:39 -0400, Jeff Moyer wrote:
> > > Christoph Hellwig <hch at 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.

Yes, commit b49a0871

> 
> > 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.

You are right. It's not about power-of-2.

Copy my old post here about why dm-thinp discard may fail with "UINT_MAX
>> 9".

      4G: 8388608 sectors
UINT_MAX: 8388607 sectors

dm-thinp block size = default discard granularity = 128 sectors

blkdev_issue_discard(sector=0, nr_sectors=8388608)

[start_sector, end_sector]
[0, 8388607]
    [0, 8388606], then dm-thinp splits it to 2 bios
        [0, 8388479]
        [8388480, 8388606] ---> this has problem in process_discard_bio(),
                                because the discard size(7 sectors) covers less than a block(128 sectors)
    [8388607, 8388607] ---> same problem 

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

[Ming Lin]

On Wed, 2015-10-21@12:19 -0400, Mike Snitzer wrote:
> On Wed, Oct 21 2015 at 12:02pm -0400,
> Mike Snitzer <snitzer@redhat.com> wrote:
> 
> > On Wed, Oct 14 2015 at  9:27am -0400,
> > Christoph Hellwig <hch@infradead.org> wrote:
> > 
> > > On Tue, Oct 13, 2015@10:44:11AM -0700, Ming Lin wrote:
> > > > I just did a quick test with a Samsung 900G NVMe device.
> > > > mkfs.xfs is OK on 4.3-rc5.
> > > > 
> > > > What's your device model? I may find a similar one to try.
> > > 
> > > This is a HGST Ultrastar SN100
> > > 
> > > Analsys and tentativ fix below:
> > > 
> > > blktrace for before the commit:
> > > 
> > > 259,0    1        2     0.000002543  2394  G   D 0 + 8388607 [mkfs.xfs]
> > > 259,0    1        3     0.000008230  2394  I   D 0 + 8388607 [mkfs.xfs]
> > > 259,0    1        4     0.000031090   207  D   D 0 + 8388607 [kworker/1:1H]
> > > 259,0    1        5     0.000044869  2394  Q   D 8388607 + 8388607 [mkfs.xfs]
> > > 259,0    1        6     0.000045992  2394  G   D 8388607 + 8388607 [mkfs.xfs]
> > > 259,0    1        7     0.000049559  2394  I   D 8388607 + 8388607 [mkfs.xfs]
> > > 259,0    1        8     0.000061551   207  D   D 8388607 + 8388607 [kworker/1:1H]
> > > 
> > > .. and so on.
> > > 
> > > blktrace with the commit:
> > > 
> > > 259,0    2        1     0.000000000  1228  Q   D 0 + 4194304 [mkfs.xfs]
> > > 259,0    2        2     0.000002543  1228  G   D 0 + 4194304 [mkfs.xfs]
> > > 259,0    2        3     0.000010080  1228  I   D 0 + 4194304 [mkfs.xfs]
> > > 259,0    2        4     0.000082187   267  D   D 0 + 4194304 [kworker/2:1H]
> > > 259,0    2        5     0.000224869  1228  Q   D 4194304 + 4194304 [mkfs.xfs]
> > > 259,0    2        6     0.000225835  1228  G   D 4194304 + 4194304 [mkfs.xfs]
> > > 259,0    2        7     0.000229457  1228  I   D 4194304 + 4194304 [mkfs.xfs]
> > > 259,0    2        8     0.000238507   267  D   D 4194304 + 4194304 [kworker/2:1H]
> > > 
> > > So discards are smaller, but better aligned.  Now if I tweak a single
> > > line in blk-lib.c to be able to use all of bi_size I get the old I/O
> > > pattern back and everything works fine again:
> > > 
> > > diff --git a/block/blk-lib.c b/block/blk-lib.c
> > > index bd40292..65b61dc 100644
> > > --- a/block/blk-lib.c
> > > +++ b/block/blk-lib.c
> > > @@ -82,7 +82,7 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
> > >  			break;
> > >  		}
> > >  
> > > -		req_sects = min_t(sector_t, nr_sects, MAX_BIO_SECTORS);
> > > +		req_sects = min_t(sector_t, nr_sects, UINT_MAX >> 9);
> > >  		end_sect = sector + req_sects;
> > >  
> > >  		bio->bi_iter.bi_sector = sector;
> > 
> > Can we change UINT_MAX >> 9 to rounddown to the first factor of
> > minimum_io_size?
> > 
> > That should work for all devices and for dm-thinp (and dm-cache) in
> > particular will ensure that all discards that are issued will be a
> > multiple of the underlying device's blocksize.
> 
> Jeff Moyer pointed out having req_sects be a factor of
> discard_granularity makes more sense.  And I agree.  Same difference in
> the end (since dm-thinp sets discard_granularity to the thinp
> blocksize).

An old version of this patch did use discard_granularity
https://www.redhat.com/archives/dm-devel/2015-August/msg00000.html

But you didn't agree.
https://www.redhat.com/archives/dm-devel/2015-August/msg00001.html

Maybe we can re-add discard_granularity now?

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

[Mike Snitzer]

On Wed, Oct 21 2015 at  1:33pm -0400,
Ming Lin <mlin@kernel.org> wrote:

> On Wed, 2015-10-21@12:19 -0400, Mike Snitzer wrote:
> > On Wed, Oct 21 2015 at 12:02pm -0400,
> > Mike Snitzer <snitzer@redhat.com> wrote:
> > 
> > > On Wed, Oct 14 2015 at  9:27am -0400,
> > > Christoph Hellwig <hch@infradead.org> wrote:
> > > 
> > > > On Tue, Oct 13, 2015@10:44:11AM -0700, Ming Lin wrote:
> > > > > I just did a quick test with a Samsung 900G NVMe device.
> > > > > mkfs.xfs is OK on 4.3-rc5.
> > > > > 
> > > > > What's your device model? I may find a similar one to try.
> > > > 
> > > > This is a HGST Ultrastar SN100
> > > > 
> > > > Analsys and tentativ fix below:
> > > > 
> > > > blktrace for before the commit:
> > > > 
> > > > 259,0    1        2     0.000002543  2394  G   D 0 + 8388607 [mkfs.xfs]
> > > > 259,0    1        3     0.000008230  2394  I   D 0 + 8388607 [mkfs.xfs]
> > > > 259,0    1        4     0.000031090   207  D   D 0 + 8388607 [kworker/1:1H]
> > > > 259,0    1        5     0.000044869  2394  Q   D 8388607 + 8388607 [mkfs.xfs]
> > > > 259,0    1        6     0.000045992  2394  G   D 8388607 + 8388607 [mkfs.xfs]
> > > > 259,0    1        7     0.000049559  2394  I   D 8388607 + 8388607 [mkfs.xfs]
> > > > 259,0    1        8     0.000061551   207  D   D 8388607 + 8388607 [kworker/1:1H]
> > > > 
> > > > .. and so on.
> > > > 
> > > > blktrace with the commit:
> > > > 
> > > > 259,0    2        1     0.000000000  1228  Q   D 0 + 4194304 [mkfs.xfs]
> > > > 259,0    2        2     0.000002543  1228  G   D 0 + 4194304 [mkfs.xfs]
> > > > 259,0    2        3     0.000010080  1228  I   D 0 + 4194304 [mkfs.xfs]
> > > > 259,0    2        4     0.000082187   267  D   D 0 + 4194304 [kworker/2:1H]
> > > > 259,0    2        5     0.000224869  1228  Q   D 4194304 + 4194304 [mkfs.xfs]
> > > > 259,0    2        6     0.000225835  1228  G   D 4194304 + 4194304 [mkfs.xfs]
> > > > 259,0    2        7     0.000229457  1228  I   D 4194304 + 4194304 [mkfs.xfs]
> > > > 259,0    2        8     0.000238507   267  D   D 4194304 + 4194304 [kworker/2:1H]
> > > > 
> > > > So discards are smaller, but better aligned.  Now if I tweak a single
> > > > line in blk-lib.c to be able to use all of bi_size I get the old I/O
> > > > pattern back and everything works fine again:
> > > > 
> > > > diff --git a/block/blk-lib.c b/block/blk-lib.c
> > > > index bd40292..65b61dc 100644
> > > > --- a/block/blk-lib.c
> > > > +++ b/block/blk-lib.c
> > > > @@ -82,7 +82,7 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
> > > >  			break;
> > > >  		}
> > > >  
> > > > -		req_sects = min_t(sector_t, nr_sects, MAX_BIO_SECTORS);
> > > > +		req_sects = min_t(sector_t, nr_sects, UINT_MAX >> 9);
> > > >  		end_sect = sector + req_sects;
> > > >  
> > > >  		bio->bi_iter.bi_sector = sector;
> > > 
> > > Can we change UINT_MAX >> 9 to rounddown to the first factor of
> > > minimum_io_size?
> > > 
> > > That should work for all devices and for dm-thinp (and dm-cache) in
> > > particular will ensure that all discards that are issued will be a
> > > multiple of the underlying device's blocksize.
> > 
> > Jeff Moyer pointed out having req_sects be a factor of
> > discard_granularity makes more sense.  And I agree.  Same difference in
> > the end (since dm-thinp sets discard_granularity to the thinp
> > blocksize).
> 
> An old version of this patch did use discard_granularity
> https://www.redhat.com/archives/dm-devel/2015-August/msg00000.html
> 
> But you didn't agree.
> https://www.redhat.com/archives/dm-devel/2015-August/msg00001.html
> 
> Maybe we can re-add discard_granularity now?

I disagreed on a more generic level than discard_granularity shaping the
split boundary.

But we are where we are.  If we're going to split (due to 32-bit limits
in bio->bi_iter.bi_size) then we should at least do so in terms of the
support discard_granularity.

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

[Ming Lin]

On Wed, 2015-10-21@14:18 -0400, Mike Snitzer wrote:
> On Wed, Oct 21 2015 at  1:33pm -0400,
> Ming Lin <mlin@kernel.org> wrote:
> 
> > On Wed, 2015-10-21@12:19 -0400, Mike Snitzer wrote:
> > > On Wed, Oct 21 2015 at 12:02pm -0400,
> > > Mike Snitzer <snitzer@redhat.com> wrote:
> > > 
> > > > On Wed, Oct 14 2015 at  9:27am -0400,
> > > > Christoph Hellwig <hch@infradead.org> wrote:
> > > > 
> > > > > On Tue, Oct 13, 2015@10:44:11AM -0700, Ming Lin wrote:
> > > > > > I just did a quick test with a Samsung 900G NVMe device.
> > > > > > mkfs.xfs is OK on 4.3-rc5.
> > > > > > 
> > > > > > What's your device model? I may find a similar one to try.
> > > > > 
> > > > > This is a HGST Ultrastar SN100
> > > > > 
> > > > > Analsys and tentativ fix below:
> > > > > 
> > > > > blktrace for before the commit:
> > > > > 
> > > > > 259,0    1        2     0.000002543  2394  G   D 0 + 8388607 [mkfs.xfs]
> > > > > 259,0    1        3     0.000008230  2394  I   D 0 + 8388607 [mkfs.xfs]
> > > > > 259,0    1        4     0.000031090   207  D   D 0 + 8388607 [kworker/1:1H]
> > > > > 259,0    1        5     0.000044869  2394  Q   D 8388607 + 8388607 [mkfs.xfs]
> > > > > 259,0    1        6     0.000045992  2394  G   D 8388607 + 8388607 [mkfs.xfs]
> > > > > 259,0    1        7     0.000049559  2394  I   D 8388607 + 8388607 [mkfs.xfs]
> > > > > 259,0    1        8     0.000061551   207  D   D 8388607 + 8388607 [kworker/1:1H]
> > > > > 
> > > > > .. and so on.
> > > > > 
> > > > > blktrace with the commit:
> > > > > 
> > > > > 259,0    2        1     0.000000000  1228  Q   D 0 + 4194304 [mkfs.xfs]
> > > > > 259,0    2        2     0.000002543  1228  G   D 0 + 4194304 [mkfs.xfs]
> > > > > 259,0    2        3     0.000010080  1228  I   D 0 + 4194304 [mkfs.xfs]
> > > > > 259,0    2        4     0.000082187   267  D   D 0 + 4194304 [kworker/2:1H]
> > > > > 259,0    2        5     0.000224869  1228  Q   D 4194304 + 4194304 [mkfs.xfs]
> > > > > 259,0    2        6     0.000225835  1228  G   D 4194304 + 4194304 [mkfs.xfs]
> > > > > 259,0    2        7     0.000229457  1228  I   D 4194304 + 4194304 [mkfs.xfs]
> > > > > 259,0    2        8     0.000238507   267  D   D 4194304 + 4194304 [kworker/2:1H]
> > > > > 
> > > > > So discards are smaller, but better aligned.  Now if I tweak a single
> > > > > line in blk-lib.c to be able to use all of bi_size I get the old I/O
> > > > > pattern back and everything works fine again:
> > > > > 
> > > > > diff --git a/block/blk-lib.c b/block/blk-lib.c
> > > > > index bd40292..65b61dc 100644
> > > > > --- a/block/blk-lib.c
> > > > > +++ b/block/blk-lib.c
> > > > > @@ -82,7 +82,7 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
> > > > >  			break;
> > > > >  		}
> > > > >  
> > > > > -		req_sects = min_t(sector_t, nr_sects, MAX_BIO_SECTORS);
> > > > > +		req_sects = min_t(sector_t, nr_sects, UINT_MAX >> 9);
> > > > >  		end_sect = sector + req_sects;
> > > > >  
> > > > >  		bio->bi_iter.bi_sector = sector;
> > > > 
> > > > Can we change UINT_MAX >> 9 to rounddown to the first factor of
> > > > minimum_io_size?
> > > > 
> > > > That should work for all devices and for dm-thinp (and dm-cache) in
> > > > particular will ensure that all discards that are issued will be a
> > > > multiple of the underlying device's blocksize.
> > > 
> > > Jeff Moyer pointed out having req_sects be a factor of
> > > discard_granularity makes more sense.  And I agree.  Same difference in
> > > the end (since dm-thinp sets discard_granularity to the thinp
> > > blocksize).
> > 
> > An old version of this patch did use discard_granularity
> > https://www.redhat.com/archives/dm-devel/2015-August/msg00000.html
> > 
> > But you didn't agree.
> > https://www.redhat.com/archives/dm-devel/2015-August/msg00001.html
> > 
> > Maybe we can re-add discard_granularity now?
> 
> I disagreed on a more generic level than discard_granularity shaping the
> split boundary.
> 
> But we are where we are.  If we're going to split (due to 32-bit limits
> in bio->bi_iter.bi_size) then we should at least do so in terms of the
> support discard_granularity.

How about below?
It actually reverts commit b49a0871 and adds patch at
https://www.redhat.com/archives/dm-devel/2015-August/msg00000.html

Christoph, could you help to try it?

commit 122bf0a43cb1611ed62aaf945f25b649c27a71ed
Author: Ming Lin <mlin at kernel.org>
Date:   Wed Oct 21 11:24:48 2015 -0700

    block: check discard_granularity and alignment
    
    Signed-off-by: Ming Lin <ming.l at ssi.samsung.com>
---
 block/blk-lib.c | 31 ++++++++++++++++++++++---------
 1 file changed, 22 insertions(+), 9 deletions(-)

diff --git a/block/blk-lib.c b/block/blk-lib.c
index bd40292..9ebf653 100644
--- a/block/blk-lib.c
+++ b/block/blk-lib.c
@@ -26,13 +26,6 @@ static void bio_batch_end_io(struct bio *bio)
 	bio_put(bio);
 }
 
-/*
- * Ensure that max discard sectors doesn't overflow bi_size and hopefully
- * it is of the proper granularity as long as the granularity is a power
- * of two.
- */
-#define MAX_BIO_SECTORS ((1U << 31) >> 9)
-
 /**
  * blkdev_issue_discard - queue a discard
  * @bdev:	blockdev to issue discard for
@@ -50,6 +43,8 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
 	DECLARE_COMPLETION_ONSTACK(wait);
 	struct request_queue *q = bdev_get_queue(bdev);
 	int type = REQ_WRITE | REQ_DISCARD;
+	unsigned int granularity;
+	int alignment;
 	struct bio_batch bb;
 	struct bio *bio;
 	int ret = 0;
@@ -61,6 +56,10 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
 	if (!blk_queue_discard(q))
 		return -EOPNOTSUPP;
 
+	/* Zero-sector (unknown) and one-sector granularities are the same.  */
+	granularity = max(q->limits.discard_granularity >> 9, 1U);
+	alignment = (bdev_discard_alignment(bdev) >> 9) % granularity;
+
 	if (flags & BLKDEV_DISCARD_SECURE) {
 		if (!blk_queue_secdiscard(q))
 			return -EOPNOTSUPP;
@@ -74,7 +73,7 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
 	blk_start_plug(&plug);
 	while (nr_sects) {
 		unsigned int req_sects;
-		sector_t end_sect;
+		sector_t end_sect, tmp;
 
 		bio = bio_alloc(gfp_mask, 1);
 		if (!bio) {
@@ -82,8 +81,22 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
 			break;
 		}
 
-		req_sects = min_t(sector_t, nr_sects, MAX_BIO_SECTORS);
+		/* Make sure bi_size doesn't overflow */
+		req_sects = min_t(sector_t, nr_sects, UINT_MAX >> 9);
+
+		/*
+		 * If splitting a request, and the next starting sector would be
+		 * misaligned, stop the discard at the previous aligned sector.
+		 */
 		end_sect = sector + req_sects;
+		tmp = end_sect;
+		if (req_sects < nr_sects &&
+		    sector_div(tmp, granularity) != alignment) {
+			end_sect = end_sect - alignment;
+			sector_div(end_sect, granularity);
+			end_sect = end_sect * granularity + alignment;
+			req_sects = end_sect - sector;
+		}
 
 		bio->bi_iter.bi_sector = sector;
 		bio->bi_end_io = bio_batch_end_io;

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

[Christoph Hellwig]

On Wed, Oct 21, 2015@01:13:09PM -0700, Ming Lin wrote:
> How about below?
> It actually reverts commit b49a0871 and adds patch at
> https://www.redhat.com/archives/dm-devel/2015-August/msg00000.html
> 
> Christoph, could you help to try it?

Still causes hickups with my controller unfortunately.

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

[Christoph Hellwig]

On Thu, Oct 22, 2015@03:24:44AM -0700, Christoph Hellwig wrote:
> > How about below?
> > It actually reverts commit b49a0871 and adds patch at
> > https://www.redhat.com/archives/dm-devel/2015-August/msg00000.html
> > 
> > Christoph, could you help to try it?
> 
> Still causes hickups with my controller unfortunately.

Turns out I booted into the wrong kernel.  This actually works fine now
thay I've actually tested the right code:

Reviewed-by: Christoph Hellwig <hch at lst.de>
Tested-by: Christoph Hellwig <hch at lst.de>