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[37.188.180.223]) by smtp.gmail.com with ESMTPSA id d10sm9067900wrp.9.2020.04.06.23.36.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 06 Apr 2020 23:36:23 -0700 (PDT) Date: Tue, 7 Apr 2020 08:36:21 +0200 From: Michal Hocko To: Yafang Shao Cc: willy@infradead.org, hannes@cmpxchg.org, vdavydov.dev@gmail.com, akpm@linux-foundation.org, linux-mm@kvack.org Subject: Re: [PATCH v2] mm, memcg: fix error return value of mem_cgroup_css_alloc() Message-ID: <20200407063621.GA18914@dhcp22.suse.cz> References: <1586188134-17038-1-git-send-email-laoar.shao@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1586188134-17038-1-git-send-email-laoar.shao@gmail.com> X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon 06-04-20 23:48:54, Yafang Shao wrote: > When I run my memcg testcase which creates lots of memcgs, I found > there're unexpected out of memory logs while there're still enough > available free memory. The error log is, > mkdir: cannot create directory 'foo.65533': Cannot allocate memory > > The reason is when we try to create more than MEM_CGROUP_ID_MAX memcgs, an > -ENOMEM errno will be set by mem_cgroup_css_alloc(), but the right errno > should be -EBUSY "Device or resource busy". That is same with > memcg_alloc_cache_id(). I do not see EBUSY being listed as expected return value for mkdir(2) which is the primary way to create a cgroup. > As the errno really misled me, we should make it right. After this patch, > the error log will be, > mkdir: cannot create directory 'foo.65533': Device or resource busy I do see ENOMEM being slightly confusing but if we really need to fix this then ENOSPC sounds like a better fit to me. man page says ENOSPC The new directory cannot be created because the user's disk quota is exhausted. and that actually matches because id is a form of a quota. > Suggested-by: Matthew Wilcox > Signed-off-by: Yafang Shao > --- > mm/memcontrol.c | 25 ++++++++++++++++++------- > 1 file changed, 18 insertions(+), 7 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index ca194864d802..94319e4dd1bd 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2717,8 +2717,12 @@ static int memcg_alloc_cache_id(void) > > id = ida_simple_get(&memcg_cache_ida, > 0, MEMCG_CACHES_MAX_SIZE, GFP_KERNEL); > - if (id < 0) > + if (id < 0) { > + if (id == -ENOSPC) > + id = -EBUSY; > + > return id; > + } > > if (id < memcg_nr_cache_ids) > return id; > @@ -4986,19 +4990,26 @@ static struct mem_cgroup *mem_cgroup_alloc(void) > unsigned int size; > int node; > int __maybe_unused i; > + long error = -ENOMEM; > > size = sizeof(struct mem_cgroup); > size += nr_node_ids * sizeof(struct mem_cgroup_per_node *); > > memcg = kzalloc(size, GFP_KERNEL); > if (!memcg) > - return NULL; > + return ERR_PTR(error); > > memcg->id.id = idr_alloc(&mem_cgroup_idr, NULL, > 1, MEM_CGROUP_ID_MAX, > GFP_KERNEL); > - if (memcg->id.id < 0) > + if (memcg->id.id < 0) { > + if (memcg->id.id == -ENOSPC) > + error = -EBUSY; > + else > + error = memcg->id.id; > + > goto fail; > + } > > memcg->vmstats_local = alloc_percpu(struct memcg_vmstats_percpu); > if (!memcg->vmstats_local) > @@ -5042,7 +5053,7 @@ static struct mem_cgroup *mem_cgroup_alloc(void) > fail: > mem_cgroup_id_remove(memcg); > __mem_cgroup_free(memcg); > - return NULL; > + return ERR_PTR(error); > } > > static struct cgroup_subsys_state * __ref > @@ -5053,8 +5064,8 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css) > long error = -ENOMEM; > > memcg = mem_cgroup_alloc(); > - if (!memcg) > - return ERR_PTR(error); > + if (IS_ERR(memcg)) > + return ERR_CAST(memcg); > > WRITE_ONCE(memcg->high, PAGE_COUNTER_MAX); > memcg->soft_limit = PAGE_COUNTER_MAX; > @@ -5104,7 +5115,7 @@ mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css) > fail: > mem_cgroup_id_remove(memcg); > mem_cgroup_free(memcg); > - return ERR_PTR(-ENOMEM); > + return ERR_PTR(error); > } > > static int mem_cgroup_css_online(struct cgroup_subsys_state *css) > -- > 2.18.1 > -- Michal Hocko SUSE Labs