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Sun, 12 Apr 2026 17:15:31 -0700 (PDT) MIME-Version: 1.0 References: <20260402063714.55124-1-liwang@redhat.com> <20260402063714.55124-8-liwang@redhat.com> In-Reply-To: <20260402063714.55124-8-liwang@redhat.com> From: Nhat Pham Date: Sun, 12 Apr 2026 17:15:20 -0700 X-Gm-Features: AQROBzCifv09xX9_r3AlbMnr7448_s_gW4fyAOGpR6oYAtKp0TkiGlmLrGMOEK8 Message-ID: Subject: Re: [PATCH v6 7/8] selftest/cgroup: fix zswap attempt_writeback() on 64K 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 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Stat-Signature: 6p76pr717e1e6e57jhss8dae93skz94z X-Rspamd-Queue-Id: E41AC180004 X-Rspamd-Server: rspam09 X-HE-Tag: 1776039332-977040 X-HE-Meta: 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 0cIJI72j 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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: > > 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/4 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. > > 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. Makes sense to me. We should scale the test by PAGE_SIZE. Acked-by: Nhat Pham