[LTP] [PATCH RFC] sync_file_range02: remove the toplimit of write back

[Li Wang]

Hi Sumit,

On Wed, Dec 18, 2019 at 6:14 PM Sumit Garg <sumit.garg@linaro.org> wrote:

> + Cyril (who originally proposed upper bound check)
>
> On Wed, 18 Dec 2019 at 14:55, Jan Stancek <jstancek@redhat.com> wrote:
> >
> >
> > ----- Original Message -----
> > > " The test's assumptions are fundamentally false; it thinks it can look
> > > at IO counters (tst_dev_bytes_written) for a disk before and after a
> > > system call, and attribute all of the IO seen to the system call that
> > > was made - this isn't necessarily correct. Other processes may generate
> > > IO in the background.
> >
> > We create our own block device, so there shouldn't be other processes
> > writing to it.
> >
> > > ext4 defers a lot of IO on a freshly made filesystem to the kernel -
> > > for example it will initialize the journal and inode tables after the
> > > mount
> >
> > Journal was my guess as well.
>
> To avoid similar scenarios, I suggested to add a "sync()" call just
> prior to test here [1]. And I couldn't reproduce the failure in
> 1000-times run with 4.19 kernel.
>

Yes, that makes sense to me.


>
> Also, I think having a "sync()" call becomes more important in case we
> remove the upper bound otherwise test might not provide reliable
> results.
>
> [1] http://lists.linux.it/pipermail/ltp/2019-October/014157.html
>
> -Sumit
>
> >
> > > Let's remove the toplimit of write back, and think as long as we synced
> > > at least the expected amount, the test passes. The +10% limit seems
> > > arbitrary.
> >
> > I think this is reasonable approach until we find better way
> > to measure what was synced.
> >
> > Acked-by: Jan Stancek <jstancek@redhat.com>
> >
> >
> > --
> > Mailing list info: https://lists.linux.it/listinfo/ltp
>
>

-- 
Regards,
Li Wang
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