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b=gaEbpmQBnJyIhLLQBSPXy7hGKEQJ0EcKljhlQsHrcFmRLuH6JXUBUirqyggrp0H/n SDMcpr7ofWrghjqkrYSjWGCnjNvSfKsDOrlsLvy5a9sH6+Kgdgapx4Q1glsgai1UW6 TK6l3/6QSFncABTi/rcejYOvG4Vz9cr4bmfHBu5U= Date: Sun, 5 Jul 2026 14:01:33 -0700 From: Andrew Morton To: Jiayuan Chen Cc: linux-mm@kvack.org, Jiayuan Chen , Johannes Weiner , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Yosry Ahmed , Nhat Pham , Chengming Zhou Subject: Re: [PATCH v2] mm: memcg: reset zswap settings in css_reset Message-Id: <20260705140133.e0534a0be91346860fd9056f@linux-foundation.org> In-Reply-To: <20260702024827.353185-1-jiayuan.chen@linux.dev> References: <20260702024827.353185-1-jiayuan.chen@linux.dev> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 0C83A1C000F X-Rspam-User: X-Stat-Signature: kqw57tymgxigjsz19w8xo59xyqpzjqu6 X-Rspamd-Server: rspam03 X-HE-Tag: 1783285294-637262 X-HE-Meta: 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 6VWNMVk5 DEE52WmkK5TmnQpjXQ8ZXGfrAlbEZcLxDTTZwL7hxoCZNLeFDWwVAH80cn5rso3VuCX83O8TFrqZGuixjokU0vF8LprOX+/f6yn5ADYSxYvF41dVA6WhxhjICErBb7QbvTuz0hfrsoZ7nN65uOexH4OaGK1BkM2jq2pUwCm7Cwj+8pLIVMpjB/a9UzUG5XuHgA1xwM0eWGQpJFkAfC3XVA7YcBZVKKUySupdZWh/b3UU8tYb36wakQpYcqh3kwbfCxPHoZuueLIy166n82od9yb2M+G7mWPTTebAqu8ECP1j9g1UZMmHT4K0TkyZqItRZzIi0DVwMy3kk9f5IxjIOi/aEBz3ymiKMtEPCZRxA8GrO3iXlUJGKlkPf13KlDZN/fLGpCgHFk0D92EMPMAKy6TL2J20hpCyNgCQ7 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, 2 Jul 2026 10:48:25 +0800 Jiayuan Chen wrote: > From: Jiayuan Chen > > mem_cgroup_css_reset() is called when the memory controller is disabled > on a cgroup but the memcg cannot be destroyed because it is pinned by a > subsystem dependency -- for example, the io controller declares > .depends_on = 1 << memory_cgrp_id, so memory remains in the cgroup_ss_mask > and the css is hidden rather than killed. > > The purpose of css_reset is to revert the memcg to its vanilla state so > that no policies are applied and the css can be safely made visible again > later. Currently, all page counters (memory.max, swap.max, kmem.max, > tcpmem.max) and other limits (soft_limit, memory.high, swap.high) are > reset to their defaults, but zswap_max and zswap_writeback are not. > > These fields are initialized in css_alloc (zswap_max = PAGE_COUNTER_MAX, > zswap_writeback inherited from parent) but were missing from css_reset. > As a result, stale zswap policies remain in effect after css_reset: the > zswap charge path (obj_cgroup_may_zswap) continues to enforce the old > zswap_max limit, and the writeback path continues to honor the old > zswap_writeback setting, even though the memory controller has been > "disabled" on this cgroup. > > Reset zswap_max to PAGE_COUNTER_MAX and zswap_writeback to true, matching > their defaults in css_alloc. > > Test: > echo "+memory +io" > /sys/fs/cgroup/cgroup.subtree_control > > mkdir /sys/fs/cgroup/test > mkdir /sys/fs/cgroup/test/child > > echo "+memory +io" > /sys/fs/cgroup/test/cgroup.subtree_control > echo 10000 > /sys/fs/cgroup/test/child/memory.zswap.max > > # child/memory.swap.max and child/memory.zswam.max disappear > echo "-memory" > /sys/fs/cgroup/test/cgroup.subtree_control > > # re-enable memory control > echo "+memory" > /sys/fs/cgroup/test/cgroup.subtree_control > > # before this patch > cat /sys/fs/cgroup/test/child/memory.zswap.max > 8192 > > # after this patch, same as memory.swap.max > cat /sys/fs/cgroup/test/child/memory.zswap.max > max Thanks. You convinced me, so I'll queue this for testing. The problem is old and doesn't sound serious, so I'll target 7.3-rc1, no cc:stable. If people disagree, please speak up. AI review suggest that memcg->oom_group is missing similar treatment: https://sashiko.dev/#/patchset/20260702024827.353185-1-jiayuan.chen@linux.dev