linux-kernel - Re: [PATCH v3 18/19] kselftests: cgroup: add kernel memory accounting tests

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Date:   Tue, 26 May 2020 08:45:08 -0700
From:   Roman Gushchin <guro@...com>
To:     Vlastimil Babka <vbabka@...e.cz>
CC:     Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>, <linux-mm@...ck.org>,
        <kernel-team@...com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3 18/19] kselftests: cgroup: add kernel memory
 accounting tests

On Tue, May 26, 2020 at 05:24:46PM +0200, Vlastimil Babka wrote:
> On 4/22/20 10:47 PM, Roman Gushchin wrote:
> > Add some tests to cover the kernel memory accounting functionality.
> > These are covering some issues (and changes) we had recently.
> > 
> > 1) A test which allocates a lot of negative dentries, checks memcg
> > slab statistics, creates memory pressure by setting memory.max
> > to some low value and checks that some number of slabs was reclaimed.
> > 
> > 2) A test which covers side effects of memcg destruction: it creates
> > and destroys a large number of sub-cgroups, each containing a
> > multi-threaded workload which allocates and releases some kernel
> > memory. Then it checks that the charge ans memory.stats do add up
> > on the parent level.
> > 
> > 3) A test which reads /proc/kpagecgroup and implicitly checks that it
> > doesn't crash the system.
> > 
> > 4) A test which spawns a large number of threads and checks that
> > the kernel stacks accounting works as expected.
> > 
> > 5) A test which checks that living charged slab objects are not
> > preventing the memory cgroup from being released after being deleted
> > by a user.
> > 
> > Signed-off-by: Roman Gushchin <guro@...com>
> > ---
> >  tools/testing/selftests/cgroup/.gitignore  |   1 +
> >  tools/testing/selftests/cgroup/Makefile    |   2 +
> >  tools/testing/selftests/cgroup/test_kmem.c | 382 +++++++++++++++++++++
> >  3 files changed, 385 insertions(+)
> >  create mode 100644 tools/testing/selftests/cgroup/test_kmem.c
> > 
> > diff --git a/tools/testing/selftests/cgroup/.gitignore b/tools/testing/selftests/cgroup/.gitignore
> > index aa6de65b0838..84cfcabea838 100644
> > --- a/tools/testing/selftests/cgroup/.gitignore
> > +++ b/tools/testing/selftests/cgroup/.gitignore
> > @@ -2,3 +2,4 @@
> >  test_memcontrol
> >  test_core
> >  test_freezer
> > +test_kmem
> > \ No newline at end of file
> > diff --git a/tools/testing/selftests/cgroup/Makefile b/tools/testing/selftests/cgroup/Makefile
> > index 967f268fde74..4794844a228e 100644
> > --- a/tools/testing/selftests/cgroup/Makefile
> > +++ b/tools/testing/selftests/cgroup/Makefile
> > @@ -6,11 +6,13 @@ all:
> >  TEST_FILES     := with_stress.sh
> >  TEST_PROGS     := test_stress.sh
> >  TEST_GEN_PROGS = test_memcontrol
> > +TEST_GEN_PROGS = test_kmem
> 
> Should be +=
> 
> >  TEST_GEN_PROGS += test_core
> >  TEST_GEN_PROGS += test_freezer
> >  
> >  include ../lib.mk
> >  
> >  $(OUTPUT)/test_memcontrol: cgroup_util.c ../clone3/clone3_selftests.h
> > +$(OUTPUT)/test_kmem: cgroup_util.c ../clone3/clone3_selftests.h
> >  $(OUTPUT)/test_core: cgroup_util.c ../clone3/clone3_selftests.h
> >  $(OUTPUT)/test_freezer: cgroup_util.c ../clone3/clone3_selftests.h
> > diff --git a/tools/testing/selftests/cgroup/test_kmem.c b/tools/testing/selftests/cgroup/test_kmem.c
> > new file mode 100644
> > index 000000000000..5bc1132fec6b
> > --- /dev/null
> > +++ b/tools/testing/selftests/cgroup/test_kmem.c
> > @@ -0,0 +1,382 @@
> ...
> > +/*
> > + * This test allocates 100000 of negative dentries with long names.
> > + * Then it checks that "slab" in memory.stat is larger than 1M.
> > + * Then it sets memory.high to 1M and checks that at least 1/2
> > + * of slab memory has been reclaimed.
> > + */
> > +static int test_kmem_basic(const char *root)
> > +{
> > +	int ret = KSFT_FAIL;
> > +	char *cg = NULL;
> > +	long slab0, slab1, current;
> > +
> > +	cg = cg_name(root, "kmem_basic_test");
> > +	if (!cg)
> > +		goto cleanup;
> > +
> > +	if (cg_create(cg))
> > +		goto cleanup;
> > +
> > +	if (cg_run(cg, alloc_dcache, (void *)100000))
> > +		goto cleanup;
> > +
> > +	slab0 = cg_read_key_long(cg, "memory.stat", "slab ");
> > +	if (slab0 < (1 >> 20))
> 
> 1 << 20 ?
> 
> Anyway I was getting this:
> not ok 1 test_kmem_basic
> ok 2 test_kmem_memcg_deletion
> ok 3 test_kmem_proc_kpagecgroup
> not ok 4 test_kmem_kernel_stacks
> ok 5 test_kmem_dead_cgroups
> 
> Adding some debugging into kmem_basic I found I get memory.stat == 0 at this
> point thus it fails the fixed test (otherwise it was failing the <= 0 test after
> writing to memory.high). But it's just a VM spinned by virtme which has a very
> simple init, so perhaps things are not as initialized as expected.

Hm, it's strange, do you have any values in memory.stat::slab for any cgroups?
Or can you send me your config (and kvm setup), I'll take a look.

Btw, thank you very much for reviewing the series! I appreciate it.
I'll integrate your feedback into the next version, which I'm working on right now.

Thanks!