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Tue, 14 May 2024 14:10:00 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id Sg2vGbhwQ2Z6NwAAD6G6ig (envelope-from ); Tue, 14 May 2024 14:10:00 +0000 Date: Tue, 14 May 2024 16:09:58 +0200 From: Michal Hocko To: Xiu Jianfeng Cc: hannes@cmpxchg.org, roman.gushchin@linux.dev, shakeel.butt@linux.dev, muchun.song@linux.dev, akpm@linux-foundation.org, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH -next] memcg: don't handle event_list for v2 when offlining Message-ID: References: <20240514131106.1326323-1-xiujianfeng@huawei.com> Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240514131106.1326323-1-xiujianfeng@huawei.com> X-Spam-Flag: NO X-Spam-Score: -2.82 X-Spam-Level: X-Spamd-Result: default: False [-2.82 / 50.00]; BAYES_HAM(-2.02)[95.17%]; NEURAL_HAM_LONG(-1.00)[-1.000]; MID_RHS_NOT_FQDN(0.50)[]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; FUZZY_BLOCKED(0.00)[rspamd.com]; DKIM_SIGNED(0.00)[suse.com:s=susede1]; ARC_NA(0.00)[]; TO_MATCH_ENVRCPT_ALL(0.00)[]; MIME_TRACE(0.00)[0:+]; FROM_HAS_DN(0.00)[]; RCVD_TLS_ALL(0.00)[]; MISSING_XM_UA(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; TO_DN_SOME(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; RCVD_VIA_SMTP_AUTH(0.00)[]; RCPT_COUNT_SEVEN(0.00)[9]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo] On Tue 14-05-24 13:11:06, Xiu Jianfeng wrote: > The event_list for memcg is only valid for v1 and not used for v2, > so it's unnessesary to handle event_list for v2. You are right but the code as is works just fine. The list will be empty. It is true that we do not need to take event_list_lock lock but nobody should be using this lock anyway. Also the offline callback is not particularly hot path. So why do we want to change the code? > > Signed-off-by: Xiu Jianfeng > --- > mm/memcontrol.c | 12 +++++++----- > 1 file changed, 7 insertions(+), 5 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index d127c9c5fabf..4254f9cd05f4 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -5881,12 +5881,14 @@ static void mem_cgroup_css_offline(struct cgroup_subsys_state *css) > * Notify userspace about cgroup removing only after rmdir of cgroup > * directory to avoid race between userspace and kernelspace. > */ > - spin_lock_irq(&memcg->event_list_lock); > - list_for_each_entry_safe(event, tmp, &memcg->event_list, list) { > - list_del_init(&event->list); > - schedule_work(&event->remove); > + if (!cgroup_subsys_on_dfl(memory_cgrp_subsys)) { > + spin_lock_irq(&memcg->event_list_lock); > + list_for_each_entry_safe(event, tmp, &memcg->event_list, list) { > + list_del_init(&event->list); > + schedule_work(&event->remove); > + } > + spin_unlock_irq(&memcg->event_list_lock); > } > - spin_unlock_irq(&memcg->event_list_lock); > > page_counter_set_min(&memcg->memory, 0); > page_counter_set_low(&memcg->memory, 0); > -- > 2.34.1 -- Michal Hocko SUSE Labs