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Wed, 17 Jun 2026 05:26:19 -0700 (PDT) Received: from localhost.localdomain ([62.77.90.70]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4606f2b0c10sm53060827f8f.21.2026.06.17.05.26.18 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 17 Jun 2026 05:26:19 -0700 (PDT) Date: Wed, 17 Jun 2026 14:26:17 +0200 From: Michal =?utf-8?Q?Koutn=C3=BD?= To: Li Wang Cc: akpm@linux-foundation.org, tj@kernel.org, longman@redhat.com, roman.gushchin@linux.dev, hannes@cmpxchg.org, yosry@kernel.org, jiayuan.chen@linux.dev, nphamcs@gmail.com, chengming.zhou@linux.dev, shuah@kernel.org, linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-kernel@vger.kernel.org, Michal Hocko , Muchun Song , Shakeel Butt Subject: Re: [PATCH v7 7/8] selftest/cgroup: fix zswap attempt_writeback() on 64K pagesize system Message-ID: References: <20260424040059.12940-1-li.wang@linux.dev> <20260424040059.12940-8-li.wang@linux.dev> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha512; 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protected-headers=v1; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Subject: Re: [PATCH v7 7/8] selftest/cgroup: fix zswap attempt_writeback() on 64K pagesize system MIME-Version: 1.0 On Fri, Apr 24, 2026 at 12:00:58PM +0800, 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. >=20 > This causes zswap_usage to be extremely small or zero, making > zswap_usage/4 insufficient to create meaningful writeback pressure. > The test then fails because no writeback is triggered. >=20 > 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. >=20 > Fix this by: > - Always allocating 1024 pages regardless of page size. This ensures > enough anonymous pages to reliably populate zswap and trigger > writeback, while keeping the original 4M allocation on 4K systems. > - Setting zswap.max to zswap_usage/4 instead of zswap_usage/2 to > create stronger writeback pressure, ensuring reclaim reliably > triggers writeback even on large page size systems. >=20 > =3D=3D=3D Error Log =3D=3D=3D > # uname -rm > 6.12.0-211.el10.ppc64le ppc64le >=20 > # getconf PAGESIZE > 65536 >=20 > # ./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 > ... >=20 > Signed-off-by: Li Wang > Cc: Johannes Weiner > Cc: Michal Hocko > Cc: Michal Koutn=FD > Cc: Muchun Song > Cc: Nhat Pham > Cc: Tejun Heo > Cc: Roman Gushchin > Cc: Shakeel Butt > Acked-by: Yosry Ahmed > Acked-by: Nhat Pham > --- > tools/testing/selftests/cgroup/test_zswap.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) Reviewed-by: Michal Koutn=FD --t4tngv5chqbx2jyz Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iJEEABYKADkWIQRCE24Fn/AcRjnLivR+PQLnlNv4CAUCajKSZRsUgAAAAAAEAA5t YW51MiwyLjUrMS4xMiwyLDIACgkQfj0C55Tb+Aho+AD/XAL/DakRMJXz9yk1Zazg v5ZtizO1OMSuDPj/gKs2+1sA/iTg96YzL1efNS85Rz0XMUIW3UE34U/bKW2+nSp8 /SII =BiG6 -----END PGP SIGNATURE----- --t4tngv5chqbx2jyz--