Re: [PATCH] generic/084: check inotify limit before tail many files

[Zirong Lang <zlang@redhat.com>]

Hi Dave,

Thanks for your reply.

----- 原始邮件 -----
> 发件人: "Dave Chinner" <david@fromorbit.com>
> 收件人: "Zorro Lang" <zlang@redhat.com>
> 抄送: fstests@vger.kernel.org, eguan@redhat.com
> 发送时间: 星期一, 2015年 8 月 17日 上午 8:03:36
> 主题: Re: [PATCH] generic/084: check inotify limit before tail many files
> 
> On Fri, Aug 14, 2015 at 12:16:32AM +0800, Zorro Lang wrote:
> > generic/084 try to run 'tail' command, tail will use
> > inotify, and there're some limit about inotify. I think
> > the most important is fs.inotify.max_user_instances, then
> > fs.inotify.max_user_watches is importand too.
> >
> > When I test on a machine with 154 cpu cores, this case
> > run failed, and hit many warning likes:
> > 
> >     tail: inotify cannot be used, reverting to polling: Too many
> >     open files
> > 
> > Because the fs.inotify.max_user_instances is 128, so if
> > we try to tail 154 files, it will be failed.
> 
> We use 'tail' all over the place in xfstests, so why is only
> generic/084 affected?

Because generic/084 use try to create $nr_cpu tail processes:
for i in `seq 1 $nr_cpu`; do
    ...
    tail -f $testfile &
    ...
done

And nr_cpu=`$here/src/feature -o`.

Generally fs.inotify.max_user_instances is 128, when a machine
have more than(or nearly the same) this number, this test will
failed.

Maybe other cases don't try to create so many tail processes, so
they passed.

> 
> And really, this seems more like a distro/environment bug and
> doesn't need xfstests help to work around. i.e. changing the
> sysctl before starting xfstests seems much more appropriate than
> hacking it a random test. Especially as there may be more than one
> test that is affected by this, and when run in a random order this
> would cause those other tests to pass/fail depending on whether
> generic/084 had already been run on that machine....

As this situation generally won't effect other cases, so I try to
make the patch don't effect more other cases. Because I don't know
if someone try to test fs.inotify...

But if maintainer think it'll be better, I will change the patch:)

Thanks,
Zorro Lang

> 
> Cheers,
> 
> Dave.
> --
> Dave Chinner
> david@fromorbit.com
>