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

[Zirong Lang <zlang@redhat.com>]

----- 原始邮件 -----
> 发件人: "Dave Chinner" <david@fromorbit.com>
> 收件人: "Zirong 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 下午 1:06:12
> 主题: Re: [PATCH] generic/084: check inotify limit before tail many files
> 
> On Sun, Aug 16, 2015 at 09:05:19PM -0400, Zirong Lang wrote:
> > 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.
> 
> This information should have been in the patch description - it's
> concurrently run tail commands that are the problem, not a single
> execution of tail...
> 
> > Maybe other cases don't try to create so many tail processes, so
> > they passed.
> 
> Exactly. The answer is obvious when you explain it fully :)
> 
> So, we have other tests that use hundreds of open unlinked files and
> they don't have this problem. That means the issue is how
> generic/084 is creating the unlinked files, not an issue with
> inotify config.
> 
> Go look at src/multi_open_unlink.c and tests/xfs/1[28]1, and then
> rewrite generic/084 to use multi_open_unlink to create and hold
> open unlinked files for a specified amount of time.

You're Great! This's a good idea to fix this problem. Thanks very much.
I have sent the V3 patch, and tested on an old kernel to sure
the bug still can be reproduced after I changed.

Thanks,
Zorro Lang

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