From c91bdc9358992856721ff77887202a7e80b7ab22 Mon Sep 17 00:00:00 2001 From: Johannes Weiner Date: Mon, 26 Sep 2022 09:57:01 -0400 Subject: [PATCH] mm: memcontrol: don't allocate cgroup swap arrays when memcg is disabled Patch series "memcg swap fix & cleanups". This patch (of 4): Since commit 2d1c498072de ("mm: memcontrol: make swap tracking an integral part of memory control"), the cgroup swap arrays are used to track memory ownership at the time of swap readahead and swapoff, even if swap space *accounting* has been turned off by the user via swapaccount=0 (which sets cgroup_memory_noswap). However, the patch was overzealous: by simply dropping the cgroup_memory_noswap conditionals in the swapon, swapoff and uncharge path, it caused the cgroup arrays being allocated even when the memory controller as a whole is disabled. This is a waste of that memory. Restore mem_cgroup_disabled() checks, implied previously by cgroup_memory_noswap, in the swapon, swapoff, and swap_entry_free callbacks. Link: https://lkml.kernel.org/r/20220926135704.400818-1-hannes@cmpxchg.org Link: https://lkml.kernel.org/r/20220926135704.400818-2-hannes@cmpxchg.org Fixes: 2d1c498072de ("mm: memcontrol: make swap tracking an integral part of memory control") Signed-off-by: Johannes Weiner Reported-by: Hugh Dickins Reviewed-by: Shakeel Butt Acked-by: Hugh Dickins Acked-by: Michal Hocko Cc: Roman Gushchin Signed-off-by: Andrew Morton --- mm/memcontrol.c | 3 +++ mm/swap_cgroup.c | 6 ++++++ 2 files changed, 9 insertions(+) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 6b74bbdc2659..9e3c010ca676 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -7459,6 +7459,9 @@ void __mem_cgroup_uncharge_swap(swp_entry_t entry, unsigned int nr_pages) struct mem_cgroup *memcg; unsigned short id; + if (mem_cgroup_disabled()) + return; + id = swap_cgroup_record(entry, 0, nr_pages); rcu_read_lock(); memcg = mem_cgroup_from_id(id); diff --git a/mm/swap_cgroup.c b/mm/swap_cgroup.c index 5a9442979a18..db6c4a26cf59 100644 --- a/mm/swap_cgroup.c +++ b/mm/swap_cgroup.c @@ -170,6 +170,9 @@ int swap_cgroup_swapon(int type, unsigned long max_pages) unsigned long length; struct swap_cgroup_ctrl *ctrl; + if (mem_cgroup_disabled()) + return 0; + length = DIV_ROUND_UP(max_pages, SC_PER_PAGE); array = vcalloc(length, sizeof(void *)); @@ -204,6 +207,9 @@ void swap_cgroup_swapoff(int type) unsigned long i, length; struct swap_cgroup_ctrl *ctrl; + if (mem_cgroup_disabled()) + return; + mutex_lock(&swap_cgroup_mutex); ctrl = &swap_cgroup_ctrl[type]; map = ctrl->map;