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Sat, 25 Nov 2023 09:38:04 -0800 (PST) Date: Sat, 25 Nov 2023 17:38:02 +0000 In-Reply-To: <20231125080137.2fhmi4374yxqjyix@CAB-WSD-L081021> Mime-Version: 1.0 References: <20231123193937.11628-1-ddrokosov@salutedevices.com> <20231123193937.11628-3-ddrokosov@salutedevices.com> <20231125063616.dex3kh3ea43ceyu3@google.com> <20231125080137.2fhmi4374yxqjyix@CAB-WSD-L081021> Message-ID: <20231125173802.pfhalf27kxk3wavy@google.com> Subject: Re: [PATCH v3 2/2] mm: memcg: introduce new event to trace shrink_memcg From: Shakeel Butt To: Dmitry Rokosov Cc: rostedt@goodmis.org, mhiramat@kernel.org, hannes@cmpxchg.org, mhocko@kernel.org, roman.gushchin@linux.dev, muchun.song@linux.dev, mhocko@suse.com, akpm@linux-foundation.org, kernel@sberdevices.ru, rockosov@gmail.com, cgroups@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org Content-Type: text/plain; charset="us-ascii" X-Rspamd-Queue-Id: 0EE7720014 X-Rspam-User: X-Stat-Signature: 6yjn6mpgfs5td1eagew9jhaqbks18yg9 X-Rspamd-Server: rspam03 X-HE-Tag: 1700933884-737439 X-HE-Meta: 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 SWVmom1T WLmLvBuuOw7oqx9FXLf5Rn8HVNGw/WPNXAsuHNi/Wsdb2utg8fugF1HZN/sz8SMDje8f2iy0BLMO8ykH2uRjJHZDap+EEr4J3rPrSrRxLdJm1NcSxuS9NUaehsB0eZdymunFG89LEi2x5T3nFxtHlRbY4biIZZV8VeQXhNimfYjBLKyLqBRG95wY5bHQ96vSWER8gi8gbzF5h1Al6pu8TjhMYx+UzOrzqjVIx5FPA+wDFTkbu+Wk1ohZXikBw+luupLJ4DajAVs9OHnIUFDUrLuDseEvwlF4P3YXDinAkUD5KsBygwRLoMVwO1q8rrsMhIKSAM3VLxmXKuQF19WkcFW6cBTqU0EzHht8h8zASQqQcQ/p5fZnai8xsu/JlLVsLbmH9sk7zc+nozz6PfMNQcVi8izG34HA6JyL2cp4xvgCgiAL/T7Vuvy7YCo/0S+vYKD5KJ7YF/F9/hFWZuQlrhV+Gp+pugNDKQjREkiOtWq5u9mI7m61ocrnibpT1c9hDNjbhA00UkeZCRvGveH7wH4rw87GNyHmo8jOor3NizMO9afjH4oBVqj+AAmCjvx9A8OCOqBqBn9EBiE37EZcTe7nt0MGV45boEqUaXa+7vAAcu6Mg/9ivA9KU9gka4use9Cu8piLH7S2gFUxxqg7s17vAeQ== X-Bogosity: Ham, tests=bogofilter, spamicity=0.323463, 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 Sat, Nov 25, 2023 at 11:01:37AM +0300, Dmitry Rokosov wrote: [...] > > > + trace_mm_vmscan_memcg_shrink_begin(sc->order, > > > + sc->gfp_mask, > > > + memcg); > > > + > > > > If you place the start of the trace here, you may have only the begin > > trace for memcgs whose usage are below their min or low limits. Is that > > fine? Otherwise you can put it just before shrink_lruvec() call. > > > > From my point of view, it's fine. For situations like the one you > described, when we only see the begin() tracepoint raised without the > end(), we understand that reclaim requests are being made but cannot be > satisfied due to certain conditions within memcg (such as limits). > > There may be some spam tracepoints in the trace pipe, which is a disadvantage > of this approach. > > How important do you think it is to understand such situations? Or do > you suggest moving the begin() tracepoint after the memcg limits checks > and don't care about it? > I was mainly wondering if that is intentional. It seems like you as first user of this trace has a need to know that a reclaim for a given memcg was triggered but due to min/low limits no reclaim was done. This is a totally reasonable use-case.