Re: [PATCH 1/2] misc: don't oom the box opening tmpfiles

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Tue, Feb 26, 2019 at 12:08:20PM -0700, Allison Henderson wrote:
> On 2/25/19 7:35 PM, Darrick J. Wong wrote:
> > From: Darrick J. Wong <darrick.wong@oracle.com>
> > 
> > For the t_open_tmpfiles tests, limit ourselves to half of file-max so
> > that we don't OOM the test machine.
> > 
> > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > ---
> >   tests/generic/530 |    2 +-
> >   tests/generic/531 |    2 +-
> >   tests/xfs/501     |    2 +-
> >   tests/xfs/502     |    2 +-
> >   4 files changed, 4 insertions(+), 4 deletions(-)
> > 
> > 
> > diff --git a/tests/generic/530 b/tests/generic/530
> > index a2968d25..2bc4a992 100755
> > --- a/tests/generic/530
> > +++ b/tests/generic/530
> > @@ -42,7 +42,7 @@ _scratch_mount
> >   # Set ULIMIT_NOFILE to min(file-max, 50000 files per LOAD_FACTOR)
> >   # so that this test doesn't take forever or OOM the box
> >   max_files=$((50000 * LOAD_FACTOR))
> > -max_allowable_files=$(( $(cat /proc/sys/fs/file-max) ))
> > +max_allowable_files=$(( $(cat /proc/sys/fs/file-max) / 2 ))
> >   test $max_allowable_files -gt 0 && test $max_files -gt $max_allowable_files && \
> >   	max_files=$max_allowable_files
> >   ulimit -n $max_files
> > diff --git a/tests/generic/531 b/tests/generic/531
> > index f3eb5cde..5d60e4b6 100755
> > --- a/tests/generic/531
> > +++ b/tests/generic/531
> > @@ -44,7 +44,7 @@ nr_cpus=$(( $(getconf _NPROCESSORS_ONLN) * 2 ))
> >   # Set ULIMIT_NOFILE to min(file-max, 50000 files per LOAD_FACTOR)
> >   # so that this test doesn't take forever or OOM the box
> >   max_files=$((50000 * LOAD_FACTOR))
> > -max_allowable_files=$(( $(cat /proc/sys/fs/file-max) ))
> > +max_allowable_files=$(( $(cat /proc/sys/fs/file-max) / 2 ))
> 
> This looks like this would certainly help, but wouldn't we want it to be
> something more like file-max - file-nr ?  Or something similar?  I'm just
> thinking the threshold at which we pop the file limit would probably be more
> dependent on how many files are already allocated about the system.  The 2
> probably solves it most of the time, but it's certainly possible that
> file-max / 2 may still be too much in some cases.  Thoughts?

Admittedly, filemax/2 is a Weasel Number -- we want to avoid running the
system out of memory, but we also have no idea how much memory actually
gets consumed by an open tempfile.  On my debug system it's 1664 bytes
for the inode, 320 bytes for the dentry, and 16 bytes for the unlinked
backref, but that's not guaranteed.  Ideally we'd stop ourselves at
(free memory / 2k) tempfiles, but the "2k" part is hard to figure.

So we just cap ourselves at filemax/2 and hope that filemax is set
sanely.  I guess we I could go for (filemax-filenr)/2?  Though that
will cause minor fluctuations in the test behavior across runs on the
same machine.

(Though really, lots of things cause fluctuations :P)

--D

> 
> Allison
> 
> >   test $max_allowable_files -gt 0 && test $max_files -gt $max_allowable_files && \
> >   	max_files=$max_allowable_files
> >   ulimit -n $max_files
> > diff --git a/tests/xfs/501 b/tests/xfs/501
> > index 51cdb020..d689145f 100755
> > --- a/tests/xfs/501
> > +++ b/tests/xfs/501
> > @@ -47,7 +47,7 @@ _scratch_mount
> >   # Set ULIMIT_NOFILE to min(file-max, 30000 files per LOAD_FACTOR)
> >   # so that this test doesn't take forever or OOM the box
> >   max_files=$((30000 * LOAD_FACTOR))
> > -max_allowable_files=$(( $(cat /proc/sys/fs/file-max) ))
> > +max_allowable_files=$(( $(cat /proc/sys/fs/file-max) / 2 ))
> >   test $max_allowable_files -gt 0 && test $max_files -gt $max_allowable_files && \
> >   	max_files=$max_allowable_files
> >   ulimit -n $max_files
> > diff --git a/tests/xfs/502 b/tests/xfs/502
> > index bfb063f4..5ad10316 100755
> > --- a/tests/xfs/502
> > +++ b/tests/xfs/502
> > @@ -46,7 +46,7 @@ nr_cpus=$(( $(getconf _NPROCESSORS_ONLN) * 2 ))
> >   # Set ULIMIT_NOFILE to min(file-max, 30000 files per cpu per LOAD_FACTOR)
> >   # so that this test doesn't take forever or OOM the box
> >   max_files=$((30000 * LOAD_FACTOR))
> > -max_allowable_files=$(( $(cat /proc/sys/fs/file-max) ))
> > +max_allowable_files=$(( $(cat /proc/sys/fs/file-max) / 2 ))
> >   test $max_allowable_files -gt 0 && test $max_files -gt $max_allowable_files && \
> >   	max_files=$max_allowable_files
> >   ulimit -n $max_files
> >