Re: [PATCH 4/4] populate: improve runtime of __populate_fill_fs

["Darrick J. Wong" <djwong@kernel.org>]

On Wed, Jan 18, 2023 at 11:54:03PM +0800, Zorro Lang wrote:
> On Tue, Jan 17, 2023 at 04:44:33PM -0800, Darrick J. Wong wrote:
> > From: Darrick J. Wong <djwong@kernel.org>
> > 
> > Run the copy loop in parallel to reduce runtime.  If filling the
> > populated fs is selected (which it isn't by default in xfs/349), this
> > reduces the runtime from ~18s to ~15s, since it's only making enough
> > copies to reduce the free space by 5%.
> > 
> > Signed-off-by: Darrick J. Wong <djwong@kernel.org>
> > ---
> >  common/populate |    3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > 
> > diff --git a/common/populate b/common/populate
> > index f34551d272..1c3c28463f 100644
> > --- a/common/populate
> > +++ b/common/populate
> > @@ -151,8 +151,9 @@ __populate_fill_fs() {
> >  	echo "FILL FS"
> >  	echo "src_sz $SRC_SZ fs_sz $FS_SZ nr $NR"
> >  	seq 2 "${NR}" | while read nr; do
> > -		cp -pRdu "${dir}/test/1" "${dir}/test/${nr}"
> > +		cp -pRdu "${dir}/test/1" "${dir}/test/${nr}" &
> >  	done
> > +	wait
> 
> I'm thinking about what'll happen if we do "Ctrl+c" on a running test which
> is waiting for these cp operations.

Hmm.  In the context of fstests running on a system with systemd, we run
each test within a systemd scope and kill the scope when the test script
exits.  That will tear down unclaimed background processes, but it's not
a hard and fast guarantee that everyone has systemd.

As for *general* bashisms, I guess the only solution is:

trap 'pkill -P $$' INT TERM QUIT EXIT

To kill all the children of the test script.  Maybe we want that?  But I
hate wrapping my brain around bash child process management, so yuck.

I'll drop the parallel populate work, it's creating a lot of problems
that I don't have time to solve while delivering only modest gains.

--D

> >  }
> >  
> >  # For XFS, force on all the quota options if quota is enabled
> > 
>