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Fri, 11 Apr 2025 08:55:39 +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 sg24JwvZ+GfiHAAAD6G6ig (envelope-from ); Fri, 11 Apr 2025 08:55:39 +0000 Message-ID: <0e9e2d5d-ec64-4ad4-a184-0c53832ff565@suse.cz> Date: Fri, 11 Apr 2025 10:55:31 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] memcg: decouple memcg_hotplug_cpu_dead from stock_lock Content-Language: en-US To: Shakeel Butt , Andrew Morton , Sebastian Andrzej Siewior Cc: Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Yosry Ahmed , Waiman Long , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Meta kernel team References: <20250410210623.1016767-1-shakeel.butt@linux.dev> From: Vlastimil Babka In-Reply-To: <20250410210623.1016767-1-shakeel.butt@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Rspamd-Queue-Id: A5453C000C X-Stat-Signature: pug3csziarz4wrbmtf58zhxzefqknyub X-Rspam-User: X-Rspamd-Server: rspam12 X-HE-Tag: 1744361741-582923 X-HE-Meta: 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 JJrVceSH ZRYr9FrwBNr5ixP/i8JvTpncgVajsfseQeBEoNgAwmK+cjpZC99ok3gSgXgmYVy5PHwRsg4D3bTqTAxwtrOj5T/JgbwEHDR4wwXViVbdbVwl3MyBEJFDrKREspdIBPDraGhWuSspPDGnjbq8hpkcGgMnCkEXH2y/bNVeb2vFUJU8FdANyVk1yH/6CdGdy6sM2k3t1G/JiwC0wZcENdp7hNEYoPaKiT31vEGb271zbqWFZs6d33FdYFxmIQbvooOZrt974Gb/s6TifkNosDCLQiM42CXYENvAPNOJuvuuWqTX6C0VcB0MmVRvisDCMbNbCQtABsfSQtiZrBNE6LQt62PBfVQ== 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: List-Subscribe: List-Unsubscribe: On 4/10/25 23:06, Shakeel Butt wrote: > The function memcg_hotplug_cpu_dead works on the stock of a remote dead > CPU and drain_obj_stock works on the given stock instead of local stock, > so there is no need to take local stock_lock anymore. > > Signed-off-by: Shakeel Butt > --- > mm/memcontrol.c | 20 ++++++++++++-------- > 1 file changed, 12 insertions(+), 8 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index f23a4d0ad239..2178a051bd09 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -1789,7 +1789,7 @@ static DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock) = { > }; > static DEFINE_MUTEX(percpu_charge_mutex); > > -static void drain_obj_stock(struct memcg_stock_pcp *stock); > +static void __drain_obj_stock(struct memcg_stock_pcp *stock); > static bool obj_stock_flush_required(struct memcg_stock_pcp *stock, > struct mem_cgroup *root_memcg); > > @@ -1873,7 +1873,7 @@ static void drain_local_stock(struct work_struct *dummy) > local_lock_irqsave(&memcg_stock.stock_lock, flags); > > stock = this_cpu_ptr(&memcg_stock); > - drain_obj_stock(stock); > + __drain_obj_stock(stock); > drain_stock(stock); > clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags); > > @@ -1964,10 +1964,10 @@ static int memcg_hotplug_cpu_dead(unsigned int cpu) > > stock = &per_cpu(memcg_stock, cpu); > > - /* drain_obj_stock requires stock_lock */ > - local_lock_irqsave(&memcg_stock.stock_lock, flags); > - drain_obj_stock(stock); > - local_unlock_irqrestore(&memcg_stock.stock_lock, flags); > + local_irq_save(flag); I think for RT this is not great? At least in theory, probably it's not actually used together with cpu hotplug? As it relies on memcg_stats_lock() I think no irq save/enable is necessary there. local_lock_irqsave wasn't actually a irq disable on RT. I don't know if there's a handy wrapper for this. > + /* stock of a remote dead cpu, no need for stock_lock. */ > + __drain_obj_stock(stock); > + local_irq_restore(flag); > > drain_stock(stock); > > @@ -2837,7 +2837,11 @@ static bool consume_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes, > return ret; > } > > -static void drain_obj_stock(struct memcg_stock_pcp *stock) > +/* > + * Works on the given stock. The callers are responsible for the proper locking > + * for the local or remote stocks. > + */ > +static void __drain_obj_stock(struct memcg_stock_pcp *stock) > { > struct obj_cgroup *old = READ_ONCE(stock->cached_objcg); > > @@ -2925,7 +2929,7 @@ static void refill_obj_stock(struct obj_cgroup *objcg, unsigned int nr_bytes, > > stock = this_cpu_ptr(&memcg_stock); > if (READ_ONCE(stock->cached_objcg) != objcg) { /* reset if necessary */ > - drain_obj_stock(stock); > + __drain_obj_stock(stock); > obj_cgroup_get(objcg); > stock->nr_bytes = atomic_read(&objcg->nr_charged_bytes) > ? atomic_xchg(&objcg->nr_charged_bytes, 0) : 0;