Re: [PATCH v1 5/5] kselftests: cgroup: add perpcu memory accounting test

[Roman Gushchin]

On Fri, Jun 05, 2020 at 08:07:51PM +0000, Dennis Zhou wrote:
> On Thu, May 28, 2020 at 04:25:08PM -0700, Roman Gushchin wrote:
> > Add a simple test to check the percpu memory accounting.
> > The test creates a cgroup tree with 1000 child cgroups
> > and checks values of memory.current and memory.stat::percpu.
> > 
> > Signed-off-by: Roman Gushchin <guro@xxxxxx>
> > ---
> >  tools/testing/selftests/cgroup/test_kmem.c | 59 ++++++++++++++++++++++
> >  1 file changed, 59 insertions(+)
> > 
> > diff --git a/tools/testing/selftests/cgroup/test_kmem.c b/tools/testing/selftests/cgroup/test_kmem.c
> > index 5224dae216e5..a0d4f1a3137d 100644
> > --- a/tools/testing/selftests/cgroup/test_kmem.c
> > +++ b/tools/testing/selftests/cgroup/test_kmem.c
> > @@ -331,6 +331,64 @@ static int test_kmem_dead_cgroups(const char *root)
> >  	return ret;
> >  }
> >  
> > +/*
> > + * This test creates a sub-tree with 1000 memory cgroups.
> > + * Then it checks that the memory.current on the parent level
> > + * is greater than 0 and approximates matches the percpu value
> > + * from memory.stat.
> > + */
> > +static int test_percpu_basic(const char *root)
> > +{
> > +	int ret = KSFT_FAIL;
> > +	char *parent, *child;
> > +	long current, percpu;
> > +	int i;
> > +
> > +	parent = cg_name(root, "percpu_basic_test");
> > +	if (!parent)
> > +		goto cleanup;
> > +
> > +	if (cg_create(parent))
> > +		goto cleanup;
> > +
> > +	if (cg_write(parent, "cgroup.subtree_control", "+memory"))
> > +		goto cleanup;
> > +
> > +	for (i = 0; i < 1000; i++) {
> > +		child = cg_name_indexed(parent, "child", i);
> > +		if (!child)
> > +			return -1;
> > +
> > +		if (cg_create(child))
> > +			goto cleanup_children;
> > +
> > +		free(child);
> > +	}
> > +
> > +	current = cg_read_long(parent, "memory.current");
> > +	percpu = cg_read_key_long(parent, "memory.stat", "percpu ");
> > +
> > +	if (current > 0 && percpu > 0 && abs(current - percpu) <
> > +	    4096 * 32 * get_nprocs())
> 
> So this is checking that we've allocated less than 32 pages per cpu over
> 1000 child cgroups that's not percpu memory? Is there a more definitive
> measurement or at least a comment we can leave saying why this limit was
> chosen.

It simple means that "current" should be approximately equal to "percpu" statistics.
Both charging and vmstat paths are using percpu batching, and the batch size is
32 pages.

I'll add a comment to make it more obvious.

Thanks!

> 
> > +		ret = KSFT_PASS;
> > +	else
> > +		printf("memory.current %ld\npercpu %ld\n",
> > +		       current, percpu);
> > +
> > +cleanup_children:
> > +	for (i = 0; i < 1000; i++) {
> > +		child = cg_name_indexed(parent, "child", i);
> > +		cg_destroy(child);
> > +		free(child);
> > +	}
> > +
> > +cleanup:
> > +	cg_destroy(parent);
> > +	free(parent);
> > +
> > +	return ret;
> > +}
> > +
> >  #define T(x) { x, #x }
> >  struct kmem_test {
> >  	int (*fn)(const char *root);
> > @@ -341,6 +399,7 @@ struct kmem_test {
> >  	T(test_kmem_proc_kpagecgroup),
> >  	T(test_kmem_kernel_stacks),
> >  	T(test_kmem_dead_cgroups),
> > +	T(test_percpu_basic),
> >  };
> >  #undef T
> >  
> > -- 
> > 2.25.4
> > 
> >