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From: Jiayuan Chen In-Reply-To: <20260630100832.107062-1-jiayuan.chen@linux.dev> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 00FC880009 X-Stat-Signature: qfm15pqr8nnzz9jjprnqtn537kfffpuk X-HE-Tag: 1782816294-328992 X-HE-Meta: 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 vAlFpRme kIsBt0MkHja18GQNKYgMgBZ4CXNuyU1rIrPQorxv5WXyi9QV3LcOam/HDt3euttT4HRL4iK+QaeyN4CuKKDW8ilB2dEyLmq46gBeWPG88UWGzCr7+H6lhd1BGgB6QSD/SRzjxN08Tfv86fnyduSXrb9G+yPZ4aVKkOL1OCFYg+0TR/h+johL6EDCwqLqwcF3BkHznfYlYSjtZAyWhx0vF4K/DiCpODoVfi//CP9PxvD9R+NVsjlsfXhMvLrlJg01zHWe3QYkHFmdUWNoFVuEPdjC+UW8QjETGZcYU652w4Ib+XIChb3Z1lWif4BMdMa0O0lUWCmqK9k33vZQryTskYMseliAvStljhnJdetznaL96jCqOKtZ+c/sHUOcpW6xP0S3jxx2QOOQtmgqQaUZeOX9Epw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 6/30/26 6:08 PM, 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 > > Cc: Jiayuan Chen > Signed-off-by: Jiayuan Chen > --- > mm/memcontrol.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index d20ffc827306..eeeb22a5e8cc 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 > + 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); https://sashiko.dev/#/patchset/20260630100832.107062-1-jiayuan.chen%40linux.dev Ai is right... Also I'm thinking that should we add a helper instead of using open code in css_alloc and  css_reset ? static void memcg_zswap_reset(struct mem_cgroup *memcg) { #ifdef CONFIG_ZSWAP     WRITE_ONCE(memcg->zswap_max, PAGE_COUNTER_MAX);     WRITE_ONCE(memcg->zswap_writeback, true); #endif } mem_cgroup_css_reset() { ... memcg_zswap_reset() ... } mem_cgroup_css_alloc() { ... memcg_zswap_reset() ... }