While installing SLES-12 (based on v4.4), I found that the installer
will stall for 60+ seconds during LVM disk scan. The root cause was
determined to be the removal of a bound device check in loop_flush()
by commit b5dd2f6047ca ("block: loop: improve performance via blk-mq").
Restoring this check, examining ->lo_state as set by loop_set_fd()
eliminates the bad behavior.
Test method:
modprobe loop max_loop=64
dd if=/dev/zero of=disk bs=512 count=200K
for((i=0;i<4;i++))do losetup -f disk; done
mkfs.ext4 -F /dev/loop0
for((i=0;i<4;i++))do mkdir t$i; mount /dev/loop$i t$i;done
for f in `ls /dev/loop[0-9]*|sort`; do \
echo $f; dd if=$f of=/dev/null bs=512 count=1; \
done
Test output: stock patched
/dev/loop0 18.1217e-05 8.3842e-05
/dev/loop1 6.1114e-05 0.000147979
/dev/loop10 0.414701 0.000116564
/dev/loop11 0.7474 6.7942e-05
/dev/loop12 0.747986 8.9082e-05
/dev/loop13 0.746532 7.4799e-05
/dev/loop14 0.480041 9.3926e-05
/dev/loop15 1.26453 7.2522e-05
Note that from loop10 onward, the device is not mounted, yet the
stock kernel consumes several orders of magnitude more wall time
than it does for a mounted device.
(Thanks for Mike Galbraith <[email protected]>, give a changelog review.)
Reviewed-by: Hannes Reinecke <[email protected]>
Reviewed-by: Ming Lei <[email protected]>
Signed-off-by: James Wang <[email protected]>
Fixes: b5dd2f6047ca ("block: loop: improve performance via blk-mq")
---
drivers/block/loop.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 48f6fa6f810e..2e5b8538760c 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -625,6 +625,9 @@ static int loop_switch(struct loop_device *lo, struct file *file)
*/
static int loop_flush(struct loop_device *lo)
{
+ /* loop not yet configured, no running thread, nothing to flush */
+ if (lo->lo_state != Lo_bound)
+ return 0;
return loop_switch(lo, NULL);
}
--
2.12.3
On 06/08/2017 08:52 AM, James Wang wrote:
> Test method:
> modprobe loop max_loop=64
> dd if=/dev/zero of=disk bs=512 count=200K
> for((i=0;i<4;i++))do losetup -f disk; done
> mkfs.ext4 -F /dev/loop0
> for((i=0;i<4;i++))do mkdir t$i; mount /dev/loop$i t$i;done
> for f in `ls /dev/loop[0-9]*|sort`; do \
> echo $f; dd if=$f of=/dev/null bs=512 count=1; \
> done
I think Christoph already asked this, but can you send a patch for
blktests [1] as well?
Thanks,
Johannes
[1] https://github.com/osandov/blktests
--
Johannes Thumshirn Storage
[email protected] +49 911 74053 689
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Felix Imendörffer, Jane Smithard, Graham Norton
HRB 21284 (AG Nürnberg)
Key fingerprint = EC38 9CAB C2C4 F25D 8600 D0D0 0393 969D 2D76 0850
On 06/08/2017 03:53 PM, Johannes Thumshirn wrote:
> On 06/08/2017 08:52 AM, James Wang wrote:
>> Test method:
>> modprobe loop max_loop=64
>> dd if=/dev/zero of=disk bs=512 count=200K
>> for((i=0;i<4;i++))do losetup -f disk; done
>> mkfs.ext4 -F /dev/loop0
>> for((i=0;i<4;i++))do mkdir t$i; mount /dev/loop$i t$i;done
>> for f in `ls /dev/loop[0-9]*|sort`; do \
>> echo $f; dd if=$f of=/dev/null bs=512 count=1; \
>> done
> I think Christoph already asked this, but can you send a patch for
> blktests [1] as well?
I have forked this project and I'm working on it.
due to framework is limited, so I'm adjusting my code.
> Thanks,
> Johannes
>
> [1] https://github.com/osandov/blktests
>
--
SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
On 06/08/2017 12:52 AM, James Wang wrote:
> While installing SLES-12 (based on v4.4), I found that the installer
> will stall for 60+ seconds during LVM disk scan. The root cause was
> determined to be the removal of a bound device check in loop_flush()
> by commit b5dd2f6047ca ("block: loop: improve performance via blk-mq").
>
> Restoring this check, examining ->lo_state as set by loop_set_fd()
> eliminates the bad behavior.
>
> Test method:
> modprobe loop max_loop=64
> dd if=/dev/zero of=disk bs=512 count=200K
> for((i=0;i<4;i++))do losetup -f disk; done
> mkfs.ext4 -F /dev/loop0
> for((i=0;i<4;i++))do mkdir t$i; mount /dev/loop$i t$i;done
> for f in `ls /dev/loop[0-9]*|sort`; do \
> echo $f; dd if=$f of=/dev/null bs=512 count=1; \
> done
>
> Test output: stock patched
> /dev/loop0 18.1217e-05 8.3842e-05
> /dev/loop1 6.1114e-05 0.000147979
> /dev/loop10 0.414701 0.000116564
> /dev/loop11 0.7474 6.7942e-05
> /dev/loop12 0.747986 8.9082e-05
> /dev/loop13 0.746532 7.4799e-05
> /dev/loop14 0.480041 9.3926e-05
> /dev/loop15 1.26453 7.2522e-05
>
> Note that from loop10 onward, the device is not mounted, yet the
> stock kernel consumes several orders of magnitude more wall time
> than it does for a mounted device.
> (Thanks for Mike Galbraith <[email protected]>, give a changelog review.)
Added for 4.12, thanks.
--
Jens Axboe