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([2601:188:c100:5710:315f:57b3:b997:5fca]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7c76e968c1fsm371472485a.52.2025.04.05.11.52.04 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 05 Apr 2025 11:52:05 -0700 (PDT) From: Waiman Long X-Google-Original-From: Waiman Long Message-ID: <6712624c-c798-4ccf-afc1-6dfc9efc4b5e@redhat.com> Date: Sat, 5 Apr 2025 14:52:04 -0400 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 v2 1/2] memcg: Don't generate low/min events if either low/min or elow/emin is 0 To: Johannes Weiner , Waiman Long Cc: Tejun Heo , Michal Hocko , Roman Gushchin , Shakeel Butt , Muchun Song , Andrew Morton , =?UTF-8?Q?Michal_Koutn=C3=BD?= , Shuah Khan , linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org References: <20250404012435.656045-1-longman@redhat.com> <1ac51e8e-8dc0-4cd8-9414-f28125061bb3@redhat.com> <20250404181308.GA300138@cmpxchg.org> <20250404193802.GA373778@cmpxchg.org> Content-Language: en-US In-Reply-To: <20250404193802.GA373778@cmpxchg.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 4/4/25 3:38 PM, Johannes Weiner wrote: > On Fri, Apr 04, 2025 at 02:55:35PM -0400, Waiman Long wrote: >> On 4/4/25 2:13 PM, Johannes Weiner wrote: >>> * Waiman points out that the weirdness is seeing low events without >>> having a low configured. Eh, this isn't really true with recursive >>> propagation; you may or may not have an elow depending on parental >>> configuration and sibling behavior. >>> >> Do you mind if we just don't update the low event count if low isn't >> set, but leave the rest the same like > What's the motivation for doing anything beyond the skip-on-!usage? It is to avoid making further change. I am fine with modifying the test to allow low event even when low isn't set. >> @@ -659,21 +659,25 @@ static inline bool mem_cgroup_unprotected(struct >> mem_cgro> >>  static inline bool mem_cgroup_below_low(struct mem_cgroup *target, >>                                         struct mem_cgroup *memcg) >>  { >> +       unsigned long elow; >> + >>         if (mem_cgroup_unprotected(target, memcg)) >>                 return false; >> >> -       return READ_ONCE(memcg->memory.elow) >= >> -               page_counter_read(&memcg->memory); >> +       elow = READ_ONCE(memcg->memory.elow); >> +       return elow && (page_counter_read(&memcg->memory) <= elow); >>  } >> >>  static inline bool mem_cgroup_below_min(struct mem_cgroup *target, >>                                         struct mem_cgroup *memcg) >>  { >> +       unsigned long emin; >> + >>         if (mem_cgroup_unprotected(target, memcg)) >>                 return false; >> >> -       return READ_ONCE(memcg->memory.emin) >= >> -               page_counter_read(&memcg->memory); >> +       emin = READ_ONCE(memcg->memory.emin); >> +       return emin && (page_counter_read(&memcg->memory) <= emin); >>  } > This still redefines the empty case to mean excess. That's a quirk I > would have liked to avoid. I don't see why you would need it? OK, I will drop that. > >> @@ -5919,7 +5923,8 @@ static void shrink_node_memcgs(pg_data_t *pgdat, >> struct s> >>                                 sc->memcg_low_skipped = 1; >>                                 continue; >>                         } >> -                       memcg_memory_event(memcg, MEMCG_LOW); >> +                       if (memcg->memory.low) >> +                               memcg_memory_event(memcg, MEMCG_LOW); > That's not right. In setups where protection comes from the parent, no > breaches would ever be counted. OK. Will post a v3 to incorporate your suggestion. Thanks, Longman