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Wed, 25 Mar 2026 00:21:20 -0700 (PDT) X-Received: by 2002:a17:903:1b28:b0:2b0:659e:97bb with SMTP id d9443c01a7336-2b0b0b0d6fcmr25894045ad.46.1774423279806; Wed, 25 Mar 2026 00:21:19 -0700 (PDT) Received: from redhat.com ([209.132.188.88]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2b083516908sm210835885ad.1.2026.03.25.00.21.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 25 Mar 2026 00:21:19 -0700 (PDT) Date: Wed, 25 Mar 2026 15:21:17 +0800 From: Li Wang To: Yosry Ahmed Cc: Andrew Morton , longman@redhat.com, yosryahmed@google.com, nphamcs@gmail.com, hannes@cmpxchg.org, mhocko@kernel.org, mkoutny@suse.com, muchun.song@linux.dev, tj@kernel.org, roman.gushchin@linux.dev, shakeel.butt@linux.dev, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH v4 0/7] selftests/cgroup: improve zswap tests robustness and support large page sizes Message-ID: References: <20260322061038.156146-1-liwang@redhat.com> <20260322091851.e965d3a2f0d6af5bd985407f@linux-foundation.org> MIME-Version: 1.0 In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: hC74YzdYbfZ4RUHod7Z2HDaUvAKS6BVDEyWnGI7q2qI_1774423280 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Rspamd-Queue-Id: 50FEF10000B X-Stat-Signature: 65sbadascw9gsfjfkhemsxru9hgx77oe X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1774423284-470376 X-HE-Meta: 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 GvlMasyu DBNsW/ADALB/xCuDc6rdfULx7/nEfHgw+EUMxscEf11J7nTvKhnIZMWO7zHEsJF2f37UfLg0ZBsj1g+ScMvjeoq3SiyRrWp1tybrt7+SSr0CnO+H7zRwfPtnnE5kf3h/nowzP0Z7Zy4wKkMetEfnx/6hFnvQBi5GYbIAtM3Y/hdj7HaGprqVGRqs7+9CjzDxROuL4l1HsRqdfZd2n/HmKcoeSeZTOXyuKL9ARDmbxsKaEkSPhHKFhLI6PiuqXqsTGSQYDB5YtqYPnM2VpZnw17kuF17PB+4GUMZTbtwexaMOAWL9y4HLJT/neWXcf5eHiHVa7raft4YWZVFJ9kH1nZ4YqcS6sgQ9ZC/0fdA+Jqz0aaBP6XOE8omOuIbPaFVGKt5Xa8jZ4knV0Pyw14cBbF3YODWGlXCVfTApWX4P0tyyekKg= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Mar 25, 2026 at 02:17:42PM +0800, Li Wang wrote: > > In summary, the problem is that 'zswpwb' does not update when zswap is executed > > under the zstd algorithm. I'd debugging this issue separately from the kernel side. Plz ignore above test logs and conclusion. > I forgot to mention, this issue only observed on systems with a 64K > pagesize (ppc64le, aarch64). I changed the aarch64 page size to 4K, > and it passed the test every time. Well, finally, I think I've found the root cause of the failure of test_no_invasive_cgroup_shrink. The test sets up two cgroups: wb_group, which is expected to trigger zswap writeback, control_group, which should have pages in zswap but must not experience any writeback. However, the data patterns used for each group are reversed: wb_group uses allocate_bytes(), which only writes a single byte per page (mem[i] = 'a'). The rest of each page is effectively zero. This data is trivially compressible, especially by zstd, so the compressed pages easily fit within zswap.max and writeback is never triggered. control_group, on the other hand, uses getrandom() to dirty 1/4 of each page, producing data that is much harder to compress. Ironically, this is the group that does not need to trigger writeback. So the test has the hard-to-compress data in the wrong cgroup. The fix is to swap the allocation patterns: wb_group should use the partially random data to ensure its compressed pages exceed zswap.max and trigger writeback, while control_group only needs simple, easily compressible data to occupy zswap. I have confirmed this when I reverse the two partens and get all passed on both lzo and zstd. Will fix in next patch version. -- Regards, Li Wang