From mboxrd@z Thu Jan 1 00:00:00 1970 From: Hugh Dickins Subject: Re: [PATCH 1/2] mm: memcontrol: don't allocate cgroup swap arrays when memcg is disabled Date: Fri, 19 Mar 2021 16:33:14 -0700 (PDT) Message-ID: References: <20210319054944.50048-1-hannes@cmpxchg.org> Mime-Version: 1.0 Return-path: DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:from:to:cc:subject:in-reply-to:message-id:references :user-agent:mime-version; bh=H5VdK/uIKMT1pp4iCjsWX5lLDmAK1g5zh8chc7mIlAc=; b=AY3pRnV72+SVoCn6bFK2m3d33V0kl3Xdda5vLh6PNQNNefCcAdDxuiD5hlz3URSd+i IVpfjCNBFk7l3OILp3flc1HpKr+lYJewEk2+hdkYf4Anssy+2hawzWNpfP0J4MipfB0G K8Zzp7g7MQNL6nWIRfRrOyvtsD0HLMAt8lC/cAY0WhmdMVriYj6dbDBOUzWsxbSW/Eer uUdcZ08zjwC4OLH1mQoBs6fBjJstKgjzJb9MLdJpa4cP/B0ZjhqjvY02td2/Xk+LcRDd nZckom5APFW679p2UegQaJ14GM8XCvZ2zQS9rWIqW79JELxZOtYzsV2e44iG9zbnfpgC uj+Q== In-Reply-To: <20210319054944.50048-1-hannes@cmpxchg.org> List-ID: Content-Type: TEXT/PLAIN; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Johannes Weiner Cc: Andrew Morton , Hugh Dickins , Shakeel Butt , Michal Hocko , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com On Fri, 19 Mar 2021, Johannes Weiner wrote: > 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. > > Fixes: 2d1c498072de ("mm: memcontrol: make swap tracking an integral part of memory control") > Reported-by: Hugh Dickins > Signed-off-by: Johannes Weiner Acked-by: Hugh Dickins Thanks for the memory! > --- > 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 668d1d7c2645..49bdcf603af1 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -7101,6 +7101,9 @@ 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 7f34343c075a..08c3246f9269 100644 > --- a/mm/swap_cgroup.c > +++ b/mm/swap_cgroup.c > @@ -171,6 +171,9 @@ 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_size = length * sizeof(void *); > > @@ -206,6 +209,9 @@ 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; > -- > 2.30.1