Re: [PATCH v3 4/5] selftests: cgroup: update per-memcg zswap writeback selftest

[Nhat Pham]

On Tue, Oct 17, 2023 at 4:34 PM Nhat Pham <nphamcs@xxxxxxxxx> wrote:
>
> On Tue, Oct 17, 2023 at 4:21 PM Nhat Pham <nphamcs@xxxxxxxxx> wrote:
> >
> > From: Domenico Cerasuolo <cerasuolodomenico@xxxxxxxxx>
> >
> > The memcg-zswap self test is updated to adjust to the behavior change
> > implemented by commit 87730b165089 ("zswap: make shrinking memcg-aware"),
> > where zswap performs writeback for specific memcg.
> >
> > Signed-off-by: Domenico Cerasuolo <cerasuolodomenico@xxxxxxxxx>
> > Signed-off-by: Nhat Pham <nphamcs@xxxxxxxxx>
>
> /s/Signed-off/Acked
> This is Domenico's work :) I used the wrong tag here. Should be:
> Acked-by: Nhat Pham <nphamcs@xxxxxxxxx>

Please ignore this comment - it was pointed out to me that Signed-off is
the appropriate tag here.

>
> > ---
> >  tools/testing/selftests/cgroup/test_zswap.c | 74 ++++++++++++++-------
> >  1 file changed, 50 insertions(+), 24 deletions(-)
> >
> > diff --git a/tools/testing/selftests/cgroup/test_zswap.c b/tools/testing/selftests/cgroup/test_zswap.c
> > index 49def87a909b..11271fabeffc 100644
> > --- a/tools/testing/selftests/cgroup/test_zswap.c
> > +++ b/tools/testing/selftests/cgroup/test_zswap.c
> > @@ -50,9 +50,9 @@ static int get_zswap_stored_pages(size_t *value)
> >         return read_int("/sys/kernel/debug/zswap/stored_pages", value);
> >  }
> >
> > -static int get_zswap_written_back_pages(size_t *value)
> > +static int get_cg_wb_count(const char *cg)
> >  {
> > -       return read_int("/sys/kernel/debug/zswap/written_back_pages", value);
> > +       return cg_read_key_long(cg, "memory.stat", "zswap_wb");
> >  }
> >
> >  static int allocate_bytes(const char *cgroup, void *arg)
> > @@ -68,45 +68,71 @@ static int allocate_bytes(const char *cgroup, void *arg)
> >         return 0;
> >  }
> >
> > +static char *setup_test_group_1M(const char *root, const char *name)
> > +{
> > +       char *group_name = cg_name(root, name);
> > +
> > +       if (!group_name)
> > +               return NULL;
> > +       if (cg_create(group_name))
> > +               goto fail;
> > +       if (cg_write(group_name, "memory.max", "1M")) {
> > +               cg_destroy(group_name);
> > +               goto fail;
> > +       }
> > +       return group_name;
> > +fail:
> > +       free(group_name);
> > +       return NULL;
> > +}
> > +
> >  /*
> >   * When trying to store a memcg page in zswap, if the memcg hits its memory
> > - * limit in zswap, writeback should not be triggered.
> > - *
> > - * This was fixed with commit 0bdf0efa180a("zswap: do not shrink if cgroup may
> > - * not zswap"). Needs to be revised when a per memcg writeback mechanism is
> > - * implemented.
> > + * limit in zswap, writeback should affect only the zswapped pages of that
> > + * memcg.
> >   */
> >  static int test_no_invasive_cgroup_shrink(const char *root)
> >  {
> > -       size_t written_back_before, written_back_after;
> >         int ret = KSFT_FAIL;
> > -       char *test_group;
> > +       size_t control_allocation_size = MB(10);
> > +       char *control_allocation, *wb_group = NULL, *control_group = NULL;
> >
> >         /* Set up */
> > -       test_group = cg_name(root, "no_shrink_test");
> > -       if (!test_group)
> > -               goto out;
> > -       if (cg_create(test_group))
> > +       wb_group = setup_test_group_1M(root, "per_memcg_wb_test1");
> > +       if (!wb_group)
> > +               return KSFT_FAIL;
> > +       if (cg_write(wb_group, "memory.zswap.max", "10K"))
> >                 goto out;
> > -       if (cg_write(test_group, "memory.max", "1M"))
> > +       control_group = setup_test_group_1M(root, "per_memcg_wb_test2");
> > +       if (!control_group)
> >                 goto out;
> > -       if (cg_write(test_group, "memory.zswap.max", "10K"))
> > +
> > +       /* Push some test_group2 memory into zswap */
> > +       if (cg_enter_current(control_group))
> >                 goto out;
> > -       if (get_zswap_written_back_pages(&written_back_before))
> > +       control_allocation = malloc(control_allocation_size);
> > +       for (int i = 0; i < control_allocation_size; i += 4095)
> > +               control_allocation[i] = 'a';
> > +       if (cg_read_key_long(control_group, "memory.stat", "zswapped") < 1)
> >                 goto out;
> >
> > -       /* Allocate 10x memory.max to push memory into zswap */
> > -       if (cg_run(test_group, allocate_bytes, (void *)MB(10)))
> > +       /* Allocate 10x memory.max to push wb_group memory into zswap and trigger wb */
> > +       if (cg_run(wb_group, allocate_bytes, (void *)MB(10)))
> >                 goto out;
> >
> > -       /* Verify that no writeback happened because of the memcg allocation */
> > -       if (get_zswap_written_back_pages(&written_back_after))
> > -               goto out;
> > -       if (written_back_after == written_back_before)
> > +       /* Verify that only zswapped memory from gwb_group has been written back */
> > +       if (get_cg_wb_count(wb_group) > 0 && get_cg_wb_count(control_group) == 0)
> >                 ret = KSFT_PASS;
> >  out:
> > -       cg_destroy(test_group);
> > -       free(test_group);
> > +       cg_enter_current(root);
> > +       if (control_group) {
> > +               cg_destroy(control_group);
> > +               free(control_group);
> > +       }
> > +       cg_destroy(wb_group);
> > +       free(wb_group);
> > +       if (control_allocation)
> > +               free(control_allocation);
> >         return ret;
> >  }
> >
> > --
> > 2.34.1