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Message-ID: <9e39ed273b5e25e3d2f33c5a2b8e3131efbfcedc.camel@yhndnzj.com>
Date: Tue, 20 Aug 2024 09:43:54 +0000
From: Mike Yuan <me@...dnzj.com>
To: Yosry Ahmed <yosryahmed@...gle.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 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?
> >
> > 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.
> > + 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.
> >
> > - if (wb != !!zswpwb_after) {
> > - ksft_print_msg("zswpwb_after is %ld while wb is
> > %s",
> > - zswpwb_after, wb ? "enabled" :
> > "disabled");
> > + if (test_zswap_writeback_one(test_group_child, wb))
> > goto out;
> > - }
> >
> > ret = KSFT_PASS;
> >
> > out:
> > + if (test_group_child) {
> > + cg_destroy(test_group_child);
> > + free(test_group_child);
> > + }
> > cg_destroy(test_group);
> > free(test_group);
> > return ret;
> > --
> > 2.46.0
> >
> >
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