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Thu, 27 Jun 2024 18:22:37 -0400 X-MC-Unique: lnK5EB3wMoaHtQ06oPb_5g-1 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-04.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 2E26919560B2; Thu, 27 Jun 2024 22:22:35 +0000 (UTC) Received: from [10.22.32.240] (unknown [10.22.32.240]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id 87CDA1955D8C; Thu, 27 Jun 2024 22:22:32 +0000 (UTC) Message-ID: <08062501-f3fb-4e4d-b72c-f1b0f964640f@redhat.com> Date: Thu, 27 Jun 2024 18:22:31 -0400 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V4 1/2] cgroup/rstat: Helper functions for locking expose trylock To: Jesper Dangaard Brouer , tj@kernel.org, cgroups@vger.kernel.org, yosryahmed@google.com, shakeel.butt@linux.dev Cc: hannes@cmpxchg.org, lizefan.x@bytedance.com, kernel-team@cloudflare.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <171952310959.1810550.17003659816794335660.stgit@firesoul> Content-Language: en-US From: Waiman Long In-Reply-To: <171952310959.1810550.17003659816794335660.stgit@firesoul> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 On 6/27/24 17:18, Jesper Dangaard Brouer wrote: > Signed-off-by: Jesper Dangaard Brouer > --- > kernel/cgroup/rstat.c | 40 ++++++++++++++++++++++++++++++---------- > 1 file changed, 30 insertions(+), 10 deletions(-) > > diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c > index fb8b49437573..2a42be3a9bb3 100644 > --- a/kernel/cgroup/rstat.c > +++ b/kernel/cgroup/rstat.c > @@ -279,17 +279,30 @@ __bpf_hook_end(); > * value -1 is used when obtaining the main lock else this is the CPU > * number processed last. > */ > -static inline void __cgroup_rstat_lock(struct cgroup *cgrp, int cpu_in_loop) > +static inline bool __cgroup_rstat_trylock(struct cgroup *cgrp, int cpu_in_loop) > +{ > + bool locked; > + > + locked = spin_trylock_irq(&cgroup_rstat_lock); > + if (!locked) > + trace_cgroup_rstat_lock_contended(cgrp, cpu_in_loop, !locked); > + > + return locked; > +} > + > +static inline void __cgroup_rstat_lock(struct cgroup *cgrp, int cpu_in_loop, > + bool check_contention) > __acquires(&cgroup_rstat_lock) > { > - bool contended; > + bool locked = false; > > - contended = !spin_trylock_irq(&cgroup_rstat_lock); > - if (contended) { > - trace_cgroup_rstat_lock_contended(cgrp, cpu_in_loop, contended); > + if (check_contention) > + locked = __cgroup_rstat_trylock(cgrp, cpu_in_loop); > + > + if (!locked) > spin_lock_irq(&cgroup_rstat_lock); > - } > - trace_cgroup_rstat_locked(cgrp, cpu_in_loop, contended); > + > + trace_cgroup_rstat_locked(cgrp, cpu_in_loop, !locked); > } > > static inline void __cgroup_rstat_unlock(struct cgroup *cgrp, int cpu_in_loop) > @@ -328,7 +341,7 @@ static void cgroup_rstat_flush_locked(struct cgroup *cgrp) > __cgroup_rstat_unlock(cgrp, cpu); > if (!cond_resched()) > cpu_relax(); > - __cgroup_rstat_lock(cgrp, cpu); > + __cgroup_rstat_lock(cgrp, cpu, true); > } > } > } > @@ -348,9 +361,16 @@ static void cgroup_rstat_flush_locked(struct cgroup *cgrp) > */ > __bpf_kfunc void cgroup_rstat_flush(struct cgroup *cgrp) > { > + bool locked; > + > might_sleep(); > > - __cgroup_rstat_lock(cgrp, -1); > + locked = __cgroup_rstat_trylock(cgrp, -1); > + if (!locked) { > + /* Opportunity to ongoing flush detection */ > + __cgroup_rstat_lock(cgrp, -1, false); > + } > + > cgroup_rstat_flush_locked(cgrp); > __cgroup_rstat_unlock(cgrp, -1); > } > @@ -368,7 +388,7 @@ void cgroup_rstat_flush_hold(struct cgroup *cgrp) > __acquires(&cgroup_rstat_lock) > { > might_sleep(); > - __cgroup_rstat_lock(cgrp, -1); > + __cgroup_rstat_lock(cgrp, -1, true); > cgroup_rstat_flush_locked(cgrp); > } > > > Will it be cleaner to add a "bool *flushed" output parameter to __cgroup_rstat_lock() so that the caller can respond differently whether the flushed flag is set or not? In that way, you don't need to expose a separate trylock() API. Also your commit log is empty. Cheers, Longman