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Message-ID: <CAJD7tkYpKA+iGFsan6B0GWT6_bOPX+83hjMQnmR11F6WX1vhiw@mail.gmail.com>
Date: Thu, 22 Aug 2024 10:47:05 -0700
From: Yosry Ahmed <yosryahmed@...gle.com>
To: Mike Yuan <me@...dnzj.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, cgroups@...r.kernel.org,
Nhat Pham <nphamcs@...il.com>, Johannes Weiner <hannes@...xchg.org>,
Andrew Morton <akpm@...ux-foundation.org>, Muchun Song <muchun.song@...ux.dev>,
Shakeel Butt <shakeel.butt@...ux.dev>, Roman Gushchin <roman.gushchin@...ux.dev>,
Michal Hocko <mhocko@...nel.org>
Subject: Re: [PATCH v2 2/2] selftests: test_zswap: add test for hierarchical zswap.writeback
On Tue, Aug 20, 2024 at 2:44 AM Mike Yuan <me@...dnzj.com> wrote:
>
> On 2024-08-19 at 12:19 -0700, Yosry Ahmed wrote:
> > On Fri, Aug 16, 2024 at 7:44 AM Mike Yuan <me@...dnzj.com> wrote:
> > >
> > > Ensure that zswap.writeback check goes up the cgroup tree.
> >
> > Too concise :) Perhaps a little bit of description of what you are
> > doing would be helpful.
>
> The patch has been merged into mm-unstable tree. Do I need to
> send a v3 to resolve the comments?
You can send a new version and Andrew usually replaces them. If the
changes are too trivial sometimes Andrew is nice enough to make
amendments directly :)
>
> > >
> > > Signed-off-by: Mike Yuan <me@...dnzj.com>
> > > ---
> > > tools/testing/selftests/cgroup/test_zswap.c | 69 ++++++++++++++---
> > > ----
> > > 1 file changed, 48 insertions(+), 21 deletions(-)
> > >
> > > diff --git a/tools/testing/selftests/cgroup/test_zswap.c
> > > b/tools/testing/selftests/cgroup/test_zswap.c
> > > index 190096017f80..7da6f9dc1066 100644
> > > --- a/tools/testing/selftests/cgroup/test_zswap.c
> > > +++ b/tools/testing/selftests/cgroup/test_zswap.c
> > > @@ -263,15 +263,13 @@ static int test_zswapin(const char *root)
> > > static int attempt_writeback(const char *cgroup, void *arg)
> > > {
> > > long pagesize = sysconf(_SC_PAGESIZE);
> > > - char *test_group = arg;
> > > size_t memsize = MB(4);
> > > char buf[pagesize];
> > > long zswap_usage;
> > > - bool wb_enabled;
> > > + bool wb_enabled = *(bool *) arg;
> > > int ret = -1;
> > > char *mem;
> > >
> > > - wb_enabled = cg_read_long(test_group,
> > > "memory.zswap.writeback");
> > > mem = (char *)malloc(memsize);
> > > if (!mem)
> > > return ret;
> > > @@ -288,12 +286,12 @@ static int attempt_writeback(const char
> > > *cgroup, void *arg)
> > > memcpy(&mem[i], buf, pagesize);
> > >
> > > /* Try and reclaim allocated memory */
> > > - if (cg_write_numeric(test_group, "memory.reclaim",
> > > memsize)) {
> > > + if (cg_write_numeric(cgroup, "memory.reclaim", memsize)) {
> > > ksft_print_msg("Failed to reclaim all of the
> > > requested memory\n");
> > > goto out;
> > > }
> > >
> > > - zswap_usage = cg_read_long(test_group,
> > > "memory.zswap.current");
> > > + zswap_usage = cg_read_long(cgroup, "memory.zswap.current");
> > >
> > > /* zswpin */
> > > for (int i = 0; i < memsize; i += pagesize) {
> > > @@ -303,7 +301,7 @@ static int attempt_writeback(const char
> > > *cgroup, void *arg)
> > > }
> > > }
> > >
> > > - if (cg_write_numeric(test_group, "memory.zswap.max",
> > > zswap_usage/2))
> > > + if (cg_write_numeric(cgroup, "memory.zswap.max",
> > > zswap_usage/2))
> > > goto out;
> > >
> > > /*
> > > @@ -312,7 +310,7 @@ static int attempt_writeback(const char
> > > *cgroup, void *arg)
> > > * If writeback is disabled, memory reclaim will fail as
> > > zswap is limited and
> > > * it can't writeback to swap.
> > > */
> > > - ret = cg_write_numeric(test_group, "memory.reclaim",
> > > memsize);
> > > + ret = cg_write_numeric(cgroup, "memory.reclaim", memsize);
> > > if (!wb_enabled)
> > > ret = (ret == -EAGAIN) ? 0 : -1;
> > >
> > > @@ -321,12 +319,38 @@ static int attempt_writeback(const char
> > > *cgroup, void *arg)
> > > return ret;
> > > }
> > >
> > > +static int test_zswap_writeback_one(const char *cgroup, bool wb)
> > > +{
> > > + long zswpwb_before, zswpwb_after;
> > > +
> > > + zswpwb_before = get_cg_wb_count(cgroup);
> > > + if (zswpwb_before != 0) {
> > > + ksft_print_msg("zswpwb_before = %ld instead of
> > > 0\n", zswpwb_before);
> > > + return -1;
> > > + }
> > > +
> > > + if (cg_run(cgroup, attempt_writeback, (void *) &wb))
> > > + return -1;
> > > +
> > > + /* Verify that zswap writeback occurred only if writeback
> > > was enabled */
> > > + zswpwb_after = get_cg_wb_count(cgroup);
> > > + if (zswpwb_after < 0)
> > > + return -1;
> > > +
> > > + if (wb != !!zswpwb_after) {
> > > + ksft_print_msg("zswpwb_after is %ld while wb is
> > > %s",
> > > + zswpwb_after, wb ? "enabled" :
> > > "disabled");
> > > + return -1;
> > > + }
> > > +
> > > + return 0;
> > > +}
> > > +
> > > /* Test to verify the zswap writeback path */
> > > static int test_zswap_writeback(const char *root, bool wb)
> > > {
> > > - long zswpwb_before, zswpwb_after;
> > > int ret = KSFT_FAIL;
> > > - char *test_group;
> > > + char *test_group, *test_group_child = NULL;
> > >
> > > test_group = cg_name(root, "zswap_writeback_test");
> > > if (!test_group)
> > > @@ -336,29 +360,32 @@ static int test_zswap_writeback(const char
> > > *root, bool wb)
> > > if (cg_write(test_group, "memory.zswap.writeback", wb ? "1"
> > > : "0"))
> > > goto out;
> > >
> > > - zswpwb_before = get_cg_wb_count(test_group);
> > > - if (zswpwb_before != 0) {
> > > - ksft_print_msg("zswpwb_before = %ld instead of
> > > 0\n", zswpwb_before);
> > > + if (test_zswap_writeback_one(test_group, wb))
> > > goto out;
> > > - }
> > >
> > > - if (cg_run(test_group, attempt_writeback, (void *)
> > > test_group))
> > > + if (cg_write(test_group, "memory.zswap.max", "max"))
> > > + goto out;
> >
> > Why is this needed? Isn't this the default value?
>
> attempt_writeback() would modify it.
Oh yes, missed that.
>
> > > + if (cg_write(test_group, "cgroup.subtree_control",
> > > "+memory"))
> > > goto out;
> > >
> > > - /* Verify that zswap writeback occurred only if writeback
> > > was enabled */
> > > - zswpwb_after = get_cg_wb_count(test_group);
> > > - if (zswpwb_after < 0)
> > > + test_group_child = cg_name(test_group,
> > > "zswap_writeback_test_child");
> > > + if (!test_group_child)
> > > + goto out;
> > > + if (cg_create(test_group_child))
> > > + goto out;
> >
> > I'd rather have all the hierarchy setup at the beginning of the test,
> > before the actual test logic. I don't feel strongly about it though.
> >
> > > + if (cg_write(test_group_child, "memory.zswap.writeback",
> > > "1"))
> > > goto out;
> >
> > Is the idea here that we always hardcode the child's zswap.writeback
> > to 1, and the parent's zswap.writeback changes from 0 to 1, and we
> > check that the parent's value is what matters?
> > I think we need a comment here.
>
> Yes, indeed.
>
> > TBH, I expected a separate test that checks different combinations of
> > parent and child values (e.g. also verifies that if the parent is
> > enabled but child is disabled, writeback is disabled).
>
> That's (implicitly) covered by the test itself IIUC? The parent cgroup
> here is in turn the child of root cgroup.
This assumes that the root has zswap writeback enabled, but that's a
fair assumption as otherwise all the writeback tests will fail.
TBH I'd prefer a standalone test rather than these implicitly tested scenarios.
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