From f11ff47ee9b06fc298e3cde5b85507048ff012e4 Mon Sep 17 00:00:00 2001 From: Jiayuan Chen Date: Thu, 2 Jul 2026 10:48:25 +0800 Subject: [PATCH] mm: memcg: reset zswap settings in css_reset 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 Link: https://lore.kernel.org/20260703063826.306878-1-jiayuan.chen@linux.dev Link: https://lore.kernel.org/20260702024827.353185-1-jiayuan.chen@linux.dev Signed-off-by: Jiayuan Chen Reviewed-by: Tao Cui Reviewed-by: Muchun Song Cc: Chengming Zhou Cc: Johannes Weiner Cc: Michal Hocko Cc: Nhat Pham Cc: Roman Gushchin Cc: Shakeel Butt Signed-off-by: Andrew Morton --- mm/memcontrol.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index d20ffc827306..c20ef3c1d6fe 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -4362,6 +4362,10 @@ static void mem_cgroup_css_reset(struct cgroup_subsys_state *css) page_counter_set_max(&memcg->memory, PAGE_COUNTER_MAX); page_counter_set_max(&memcg->swap, PAGE_COUNTER_MAX); +#ifdef CONFIG_ZSWAP + WRITE_ONCE(memcg->zswap_max, PAGE_COUNTER_MAX); + WRITE_ONCE(memcg->zswap_writeback, true); +#endif #ifdef CONFIG_MEMCG_V1 page_counter_set_max(&memcg->kmem, PAGE_COUNTER_MAX); page_counter_set_max(&memcg->tcpmem, PAGE_COUNTER_MAX);