Re: [PATCH v2] fstest: btrfs: test single 4k extent after subpagesize buffered writes

[Eryu Guan <eguan@redhat.com>]

On Tue, Mar 22, 2016 at 03:12:25PM -0700, Liu Bo wrote:
> On Tue, Mar 22, 2016 at 12:00:13PM +0800, Eryu Guan wrote:
> > On Thu, Mar 17, 2016 at 03:56:38PM -0700, Liu Bo wrote:
> > > This is to test if COW enabled btrfs can end up with single 4k extents
> > > when doing subpagesize buffered writes.
> > 
> > What happens if btrfs is mounted with "nodatacow" option? Does it need
> > to _notrun if cow is disabled?
> 
> In my test, the test passes if mounting with "nodatacow".
> Yes, it makes sense to have a _notrun for nodatacow.

If "nodatacow" btrfs should pass the test as well, then I don't think
_notrun is needed, so when it failed, something went wrong.

> 
> > 
> > > 
> > > The patch to fix the problem is
> > >   https://patchwork.kernel.org/patch/8527991/
> > > 
> > > Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
> > > ---
> > > v2: - Teach awk to know system's pagesize.
> > >     - Add "Silence is golden" to output.
> > >     - Use local variables to lower case.
> > >     - Add comments to make code clear.
> > 
> > This should be v3, and this patch was buried in the v2 thread :)
> 
> Oops, thanks for pointing it out.
> 
> > 
> > > 
> > >  tests/btrfs/027     | 102 ++++++++++++++++++++++++++++++++++++++++++++++++++++
> > >  tests/btrfs/027.out |   2 ++
> > >  tests/btrfs/group   |   1 +
> > >  3 files changed, 105 insertions(+)
> > >  create mode 100755 tests/btrfs/027
> > >  create mode 100644 tests/btrfs/027.out
> > > 
> > > diff --git a/tests/btrfs/027 b/tests/btrfs/027
> > > new file mode 100755
> > > index 0000000..19d324b
> > > --- /dev/null
> > > +++ b/tests/btrfs/027
> > > @@ -0,0 +1,102 @@
> > > +#! /bin/bash
> > > +# FS QA Test 027
> > > +#
> > > +# When btrfs is using cow mode, buffered writes of sub-pagesize can end up with
> > > +# single 4k extents.
> > > +# Ref:
> > > +#     "Stray 4k extents with slow buffered writes"
> > > +#     https://www.spinics.net/lists/linux-btrfs/msg52628.html
> > 
> > After going through this thread, my understanding is that nodatacow
> > btrfs should pass this test even on unpatched kernel (e.g. v4.5). But
> > my test on v4.5 kernel failed with nodatacow mount option, pagesize
> > extent is still found.
> > 
> 
> I verified it again on my kvm box and it passed with a unpatched v4.5 kernel.
> 
> Can you please show me the 027.full file?
> 
> I can't think of a reason for this..

I'm using v4.5 kernel and v4.4 btrfs-progs, and it's not reproduced
everytime.

SECTION       -- btrfs_nodatacow
RECREATING    -- btrfs on /dev/sda5
FSTYP         -- btrfs
PLATFORM      -- Linux/x86_64 dhcp-66-86-11 4.5.0
MKFS_OPTIONS  -- /dev/sda6
MOUNT_OPTIONS -- -o nodatacow -o context=system_u:object_r:nfs_t:s0 /dev/sda6 /mnt/testarea/scratch

btrfs/027 28s ... - output mismatch (see /root/xfstests/results//btrfs_nodatacow/btrfs/027.out.bad)
    --- tests/btrfs/027.out     2016-03-23 15:39:41.562000000 +0800
    +++ /root/xfstests/results//btrfs_nodatacow/btrfs/027.out.bad       2016-03-23 19:37:38.962000000 +0800
    @@ -1,2 +1,3 @@
     QA output created by 027
     Silence is golden
    +8
    ...
    (Run 'diff -u tests/btrfs/027.out /root/xfstests/results//btrfs_nodatacow/btrfs/027.out.bad'  to see the entire diff)
Ran: btrfs/027
Failures: btrfs/027
Failed 1 of 1 tests

And btrfs/027.full shows:

/mnt/testarea/scratch/testfile:
 EXT: FILE-OFFSET      BLOCK-RANGE      TOTAL FLAGS
   0: [0..28863]:      2154496..2183359 28864   0x0
   1: [28864..57751]:  2183360..2212247 28888   0x0
   2: [57752..85543]:  2212248..2240039 27792   0x0
   3: [85544..113239]: 2240040..2267735 27696   0x0
   4: [113240..113247]: 2267736..2267743     8   0x0
   5: [113248..141999]: 2267744..2296495 28752   0x0
   6: [142000..142023]: 2296496..2296519    24   0x0
   7: [142024..159799]: 2296520..2314295 17776   0x1

Thanks,
Eryu