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[67.188.127.15]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-7349fe48873sm3906691b3a.49.2025.02.28.08.07.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 28 Feb 2025 08:07:52 -0800 (PST) Message-ID: <066a7505-a4fe-4b76-b7a6-ae97f786dac7@gmail.com> Date: Fri, 28 Feb 2025 08:07:50 -0800 Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 3/4 v2] cgroup: separate rstat locks for subsystems To: Shakeel Butt Cc: tj@kernel.org, yosryahmed@google.com, mhocko@kernel.org, hannes@cmpxchg.org, akpm@linux-foundation.org, linux-mm@kvack.org, cgroups@vger.kernel.org, kernel-team@meta.com References: <20250227215543.49928-1-inwardvessel@gmail.com> <20250227215543.49928-4-inwardvessel@gmail.com> Content-Language: en-US From: JP Kobryn In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 2/27/25 2:52 PM, Shakeel Butt wrote: > On Thu, Feb 27, 2025 at 01:55:42PM -0800, inwardvessel wrote: >> From: JP Kobryn >> >> Let the existing locks be dedicated to the base stats and rename them as >> such. Also add new rstat locks for each enabled subsystem. When handling >> cgroup subsystem states, distinguish between formal subsystems (memory, >> io, etc) and the base stats subsystem state (represented by >> cgroup::self) to decide on which locks to take. This change is made to >> prevent contention between subsystems when updating/flushing stats. >> >> Signed-off-by: JP Kobryn > > Couple of nits below otherwise: > > Reviewed-by: Shakeel Butt > >> --- >> kernel/cgroup/rstat.c | 93 +++++++++++++++++++++++++++++++++---------- >> 1 file changed, 72 insertions(+), 21 deletions(-) >> >> diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c >> index 88908ef9212d..b3eaefc1fd07 100644 >> --- a/kernel/cgroup/rstat.c >> +++ b/kernel/cgroup/rstat.c >> @@ -9,8 +9,12 @@ >> >> #include >> >> -static DEFINE_SPINLOCK(cgroup_rstat_lock); >> -static DEFINE_PER_CPU(raw_spinlock_t, cgroup_rstat_cpu_lock); >> +static DEFINE_SPINLOCK(cgroup_rstat_base_lock); >> +static DEFINE_PER_CPU(raw_spinlock_t, cgroup_rstat_base_cpu_lock); >> + >> +static spinlock_t cgroup_rstat_subsys_lock[CGROUP_SUBSYS_COUNT]; >> +static DEFINE_PER_CPU(raw_spinlock_t, >> + cgroup_rstat_subsys_cpu_lock[CGROUP_SUBSYS_COUNT]); >> > > The name of these locks are too long and you had to go multi-line. > Please just reduce the size of the names. These are local to this file, > so maybe you can drop cgroup_rstat_ from them or keep the rstat. Agreed. Will do in next rev. > >> static void cgroup_base_stat_flush(struct cgroup *cgrp, int cpu); >> >> @@ -20,8 +24,13 @@ static struct cgroup_rstat_cpu *cgroup_rstat_cpu( >> return per_cpu_ptr(css->rstat_cpu, cpu); >> } >> >> +static inline bool is_base_css(struct cgroup_subsys_state *css) >> +{ >> + return css->ss == NULL; >> +} >> + >> /* >> - * Helper functions for rstat per CPU lock (cgroup_rstat_cpu_lock). >> + * Helper functions for rstat per CPU locks. >> * >> * This makes it easier to diagnose locking issues and contention in >> * production environments. The parameter @fast_path determine the >> @@ -36,12 +45,12 @@ unsigned long _cgroup_rstat_cpu_lock(raw_spinlock_t *cpu_lock, int cpu, >> bool contended; >> >> /* >> - * The _irqsave() is needed because cgroup_rstat_lock is >> - * spinlock_t which is a sleeping lock on PREEMPT_RT. Acquiring >> - * this lock with the _irq() suffix only disables interrupts on >> - * a non-PREEMPT_RT kernel. The raw_spinlock_t below disables >> - * interrupts on both configurations. The _irqsave() ensures >> - * that interrupts are always disabled and later restored. >> + * The _irqsave() is needed because the locks used for flushing are >> + * spinlock_t which is a sleeping lock on PREEMPT_RT. Acquiring this lock >> + * with the _irq() suffix only disables interrupts on a non-PREEMPT_RT >> + * kernel. The raw_spinlock_t below disables interrupts on both >> + * configurations. The _irqsave() ensures that interrupts are always >> + * disabled and later restored. >> */ >> contended = !raw_spin_trylock_irqsave(cpu_lock, flags); >> if (contended) { >> @@ -87,7 +96,7 @@ __bpf_kfunc void cgroup_rstat_updated( >> struct cgroup_subsys_state *css, int cpu) >> { >> struct cgroup *cgrp = css->cgroup; >> - raw_spinlock_t *cpu_lock = per_cpu_ptr(&cgroup_rstat_cpu_lock, cpu); >> + raw_spinlock_t *cpu_lock; >> unsigned long flags; >> >> /* >> @@ -101,6 +110,12 @@ __bpf_kfunc void cgroup_rstat_updated( >> if (data_race(cgroup_rstat_cpu(css, cpu)->updated_next)) >> return; >> >> + if (is_base_css(css)) >> + cpu_lock = per_cpu_ptr(&cgroup_rstat_base_cpu_lock, cpu); >> + else >> + cpu_lock = per_cpu_ptr(cgroup_rstat_subsys_cpu_lock, cpu) + >> + css->ss->id; > > Use the array index here like cgroup_rstat_subsys_cpu_lock[css->ss->id]. Good call. I see the arithmetic may be more appropriate in cases where the per-cpu array/buffer is dynamic. I'll use the index notation in v3. > >> + >> flags = _cgroup_rstat_cpu_lock(cpu_lock, cpu, cgrp, true); >> >> /* put @css and all ancestors on the corresponding updated lists */ >> @@ -208,11 +223,17 @@ static struct cgroup_subsys_state *cgroup_rstat_updated_list( >> struct cgroup_subsys_state *root, int cpu) >> { >> struct cgroup *cgrp = root->cgroup; >> - raw_spinlock_t *cpu_lock = per_cpu_ptr(&cgroup_rstat_cpu_lock, cpu); >> struct cgroup_rstat_cpu *rstatc = cgroup_rstat_cpu(root, cpu); >> struct cgroup_subsys_state *head = NULL, *parent, *child; >> + raw_spinlock_t *cpu_lock; >> unsigned long flags; >> >> + if (is_base_css(root)) >> + cpu_lock = per_cpu_ptr(&cgroup_rstat_base_cpu_lock, cpu); >> + else >> + cpu_lock = per_cpu_ptr(cgroup_rstat_subsys_cpu_lock, cpu) + >> + root->ss->id; > > Same here. > >> + >> flags = _cgroup_rstat_cpu_lock(cpu_lock, cpu, cgrp, false); >> >> /* Return NULL if this subtree is not on-list */ >> @@ -315,7 +336,7 @@ static void cgroup_rstat_flush_locked(struct cgroup_subsys_state *css, >> struct cgroup *cgrp = css->cgroup; >> int cpu; >> >> - lockdep_assert_held(&cgroup_rstat_lock); >> + lockdep_assert_held(&lock); >> >> for_each_possible_cpu(cpu) { >> struct cgroup_subsys_state *pos; >> @@ -356,12 +377,18 @@ static void cgroup_rstat_flush_locked(struct cgroup_subsys_state *css, >> __bpf_kfunc void cgroup_rstat_flush(struct cgroup_subsys_state *css) >> { >> struct cgroup *cgrp = css->cgroup; >> + spinlock_t *lock; >> + >> + if (is_base_css(css)) >> + lock = &cgroup_rstat_base_lock; >> + else >> + lock = &cgroup_rstat_subsys_lock[css->ss->id]; >> >> might_sleep(); >> >> - __cgroup_rstat_lock(&cgroup_rstat_lock, cgrp, -1); >> - cgroup_rstat_flush_locked(css, &cgroup_rstat_lock); >> - __cgroup_rstat_unlock(&cgroup_rstat_lock, cgrp, -1); >> + __cgroup_rstat_lock(lock, cgrp, -1); >> + cgroup_rstat_flush_locked(css, lock); >> + __cgroup_rstat_unlock(lock, cgrp, -1); >> } >> >> /** >> @@ -376,10 +403,16 @@ __bpf_kfunc void cgroup_rstat_flush(struct cgroup_subsys_state *css) >> void cgroup_rstat_flush_hold(struct cgroup_subsys_state *css) >> { >> struct cgroup *cgrp = css->cgroup; >> + spinlock_t *lock; >> + >> + if (is_base_css(css)) >> + lock = &cgroup_rstat_base_lock; >> + else >> + lock = &cgroup_rstat_subsys_lock[css->ss->id]; >> >> might_sleep(); >> - __cgroup_rstat_lock(&cgroup_rstat_lock, cgrp, -1); >> - cgroup_rstat_flush_locked(css, &cgroup_rstat_lock); >> + __cgroup_rstat_lock(lock, cgrp, -1); >> + cgroup_rstat_flush_locked(css, lock); >> } >> >> /** >> @@ -389,7 +422,14 @@ void cgroup_rstat_flush_hold(struct cgroup_subsys_state *css) >> void cgroup_rstat_flush_release(struct cgroup_subsys_state *css) >> { >> struct cgroup *cgrp = css->cgroup; >> - __cgroup_rstat_unlock(&cgroup_rstat_lock, cgrp, -1); >> + spinlock_t *lock; >> + >> + if (is_base_css(css)) >> + lock = &cgroup_rstat_base_lock; >> + else >> + lock = &cgroup_rstat_subsys_lock[css->ss->id]; >> + >> + __cgroup_rstat_unlock(lock, cgrp, -1); >> } >> >> int cgroup_rstat_init(struct cgroup_subsys_state *css) >> @@ -435,10 +475,21 @@ void cgroup_rstat_exit(struct cgroup_subsys_state *css) >> >> void __init cgroup_rstat_boot(void) >> { >> - int cpu; >> + struct cgroup_subsys *ss; >> + int cpu, ssid; >> >> - for_each_possible_cpu(cpu) >> - raw_spin_lock_init(per_cpu_ptr(&cgroup_rstat_cpu_lock, cpu)); >> + for_each_subsys(ss, ssid) { >> + spin_lock_init(&cgroup_rstat_subsys_lock[ssid]); >> + } >> + >> + for_each_possible_cpu(cpu) { >> + raw_spin_lock_init(per_cpu_ptr(&cgroup_rstat_base_cpu_lock, cpu)); >> + >> + for_each_subsys(ss, ssid) { >> + raw_spin_lock_init( >> + per_cpu_ptr(cgroup_rstat_subsys_cpu_lock, cpu) + ssid); > > Same here. > >> + } >> + } >> } >> >> /* >> -- >> 2.43.5 >>