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Wed, 11 Mar 2026 19:38:29 -0700 (PDT) Received: from redhat.com ([209.132.188.88]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-c73cdf0e99dsm3151428a12.7.2026.03.11.19.38.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 11 Mar 2026 19:38:28 -0700 (PDT) Date: Thu, 12 Mar 2026 10:38:26 +0800 From: Li Wang To: Yosry Ahmed Cc: linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, Johannes Weiner , Michal Hocko , Michal =?utf-8?Q?Koutn=C3=BD?= , Muchun Song , Nhat Pham , Tejun Heo , Roman Gushchin , Shakeel Butt Subject: Re: [PATCH 5/5] selftest/cgroup: fix zswap attempt_writeback() on 64K pagesize system Message-ID: References: <20260311110523.26624-1-liwang@redhat.com> <20260311110523.26624-5-liwang@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Wed, Mar 11, 2026 at 11:58:34AM -0700, Yosry Ahmed wrote: > On Wed, Mar 11, 2026 at 4:06 AM Li Wang wrote: > > > > In attempt_writeback(), a memsize of 4M only covers 64 pages on 64K > > page size systems. When memory.reclaim is called, the kernel prefers > > reclaiming clean file pages (binary, libc, linker, etc.) over swapping > > anonymous pages. With only 64 pages of anonymous memory, the reclaim > > target can be largely or entirely satisfied by dropping file pages, > > resulting in very few or zero anonymous pages being pushed into zswap. > > > > This causes zswap_usage to be extremely small or zero, making > > zswap_usage/2 insufficient to create meaningful writeback pressure. > > The test then fails because no writeback is triggered. > > > > On 4K page size systems this is not an issue because 4M covers 1024 > > pages, and file pages are a small fraction of the reclaim target. > > > > Scale memsize up to 64M on systems with page size larger than 4K, so > > that enough anonymous pages are allocated to reliably populate zswap > > and trigger writeback. The original 4M is kept for 4K page size systems > > to avoid unnecessary memory usage and test runtime. > > > > === Error Log === > > # uname -rm > > 6.12.0-211.el10.ppc64le ppc64le > > > > # getconf PAGESIZE > > 65536 > > > > # ./test_zswap > > TAP version 13 > > 1..7 > > ok 1 test_zswap_usage > > ok 2 test_swapin_nozswap > > ok 3 test_zswapin > > not ok 4 test_zswap_writeback_enabled > > ... > > > > Signed-off-by: Li Wang > > Cc: Johannes Weiner > > Cc: Michal Hocko > > Cc: Michal Koutný > > Cc: Muchun Song > > Cc: Nhat Pham > > Cc: Tejun Heo > > Cc: Roman Gushchin > > Cc: Shakeel Butt > > Cc: Yosry Ahmed > > --- > > tools/testing/selftests/cgroup/test_zswap.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/tools/testing/selftests/cgroup/test_zswap.c b/tools/testing/selftests/cgroup/test_zswap.c > > index 30d3fbf6b4fb..2d065184eea4 100644 > > --- a/tools/testing/selftests/cgroup/test_zswap.c > > +++ b/tools/testing/selftests/cgroup/test_zswap.c > > @@ -264,7 +264,7 @@ static int test_zswapin(const char *root) > > static int attempt_writeback(const char *cgroup, void *arg) > > { > > long pagesize = sysconf(_SC_PAGESIZE); > > - size_t memsize = MB(4); > > + size_t memsize = pagesize > 4096 ? MB(64): MB(4); > > pagesize << 10 or pagesize * 1024? Sure, I will go pagesize * 1024 which clearly shows the numbers of page. -- Regards, Li Wang