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Sun, 12 Apr 2026 17:29:47 -0700 (PDT) MIME-Version: 1.0 References: <20260402063714.55124-1-liwang@redhat.com> <20260402063714.55124-7-liwang@redhat.com> In-Reply-To: <20260402063714.55124-7-liwang@redhat.com> From: Nhat Pham Date: Sun, 12 Apr 2026 17:29:35 -0700 X-Gm-Features: AQROBzDA_W2wnhZr93RNMhtdQJumotHsjmSnSZPteOoUEt7sHLGd9BTXQt8gj-w Message-ID: Subject: Re: [PATCH v6 6/8] selftest/cgroup: fix zswap test_no_invasive_cgroup_shrink on large pagesize system To: Li Wang Cc: akpm@linux-foundation.org, rppt@kernel.org, david@kernel.org, hannes@cmpxchg.org, yosry@kernel.org, ljs@kernel.org, Liam.Howlett@oracle.com, mhocko@suse.com, shuah@kernel.org, chengming.zhou@linux.dev, longman@redhat.com, linux-mm@kvack.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, Michal Hocko , =?UTF-8?Q?Michal_Koutn=C3=BD?= , Muchun Song , Tejun Heo , Roman Gushchin , Shakeel Butt , Yosry Ahmed Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 88507180005 X-Stat-Signature: 9yzhbeqsnxiw6ggs5x83mj91j4z7psgt X-Rspam-User: X-HE-Tag: 1776040189-178771 X-HE-Meta: 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 BYBkXHjB 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Apr 1, 2026 at 11:38=E2=80=AFPM Li Wang wrote: > > test_no_invasive_cgroup_shrink sets up two cgroups: wb_group, which is > expected to trigger zswap writeback, and a control group (renamed to > zw_group), which should only have pages sitting in zswap without any > writeback. > > There are two problems with the current test: > > 1) The data patterns are reversed. wb_group uses allocate_bytes(), which > writes only a single byte per page =E2=80=94 trivially compressible, > especially by zstd =E2=80=94 so compressed pages fit within zswap.max = and > writeback is never triggered. Meanwhile, the control group uses > getrandom() to produce hard-to-compress data, but it is the group > that does *not* need writeback. > > 2) The test uses fixed sizes (10K zswap.max, 10MB allocation) that are > too small on systems with large PAGE_SIZE (e.g. 64K), failing to > build enough memory pressure to trigger writeback reliably. > > Fix both issues by: > - Swapping the data patterns: fill wb_group pages with partially > random data (getrandom for page_size/4 bytes) to resist compression > and trigger writeback, and fill zw_group pages with simple repeated > data to stay compressed in zswap. > - Making all size parameters PAGE_SIZE-aware: set allocation size to > PAGE_SIZE * 1024, memory.zswap.max to PAGE_SIZE, and memory.max to > allocation_size / 2 for both cgroups. > - Allocating memory inline instead of via cg_run() so the pages > remain resident throughout the test. > > =3D=3D=3D Error Log =3D=3D=3D > # getconf PAGESIZE > 65536 > > # ./test_zswap > TAP version 13 > ... > ok 5 test_zswap_writeback_disabled > ok 6 # SKIP test_no_kmem_bypass > not ok 7 test_no_invasive_cgroup_shrink I assume the test passed after fix? ;) > > Signed-off-by: Li Wang > Cc: Johannes Weiner > Cc: Michal Hocko > Cc: Michal Koutn=C3=BD > Cc: Muchun Song > Cc: Nhat Pham > Cc: Tejun Heo > Cc: Roman Gushchin > Cc: Shakeel Butt > Cc: Yosry Ahmed > --- > > Notes: > v5: > - Swap data patterns: use getrandom() for wb_group and simple > memset for zw_group to fix the reversed allocation logic. > - Rename control_group to zw_group for clarity. > - Allocate memory inline instead of via cg_run() so pages remain > resident throughout the test. > > tools/testing/selftests/cgroup/test_zswap.c | 70 ++++++++++++++------- > 1 file changed, 49 insertions(+), 21 deletions(-) LGTM. Thanks for fixing the tests :) Acked-by: Nhat Pham