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From: Shakeel Butt To: Yosry Ahmed Cc: Jesper Dangaard Brouer , tj@kernel.org, cgroups@vger.kernel.org, hannes@cmpxchg.org, lizefan.x@bytedance.com, longman@redhat.com, kernel-team@cloudflare.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH V2] cgroup/rstat: Avoid thundering herd problem by kswapd across NUMA nodes Message-ID: References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 818D31C001D X-Stat-Signature: a79isq9w8nk3dzhwgtx5dna7nkzh1kf5 X-HE-Tag: 1719332512-720474 X-HE-Meta: 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 4hEzoKZf 3AsGP/Xl6iHJLsf3FxptNQC24MJLNxWMDYmi0hziNSr8rGPa8XpQNrmxl42EUF44UkHH6I0x8g76K2hHtq8J54DGchsQcvcnvbRIBohcWu9AENOhfYvlnKjoKgTgAwcWECiOm8Q30e9C7dHUr3NuaiN8MVUWusQDmJX4i X-Bogosity: Ham, tests=bogofilter, spamicity=0.002694, 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 Tue, Jun 25, 2024 at 09:00:03AM GMT, Yosry Ahmed wrote: [...] > > My point is not about accuracy, although I think it's a reasonable > argument on its own (a lot of things could change in a short amount of > time, which is why I prefer magnitude-based ratelimiting). > > My point is about logical ordering. If a userspace program reads the > stats *after* an event occurs, it expects to get a snapshot of the > system state after that event. Two examples are: > > - A proactive reclaimer reading the stats after a reclaim attempt to > check if it needs to reclaim more memory or fallback. > - A userspace OOM killer reading the stats after a usage spike to > decide which workload to kill. > > I listed such examples with more detail in [1], when I removed > stats_flush_ongoing from the memcg code. > > [1]https://lore.kernel.org/lkml/20231129032154.3710765-6-yosryahmed@google.com/ You are kind of arbitrarily adding restrictions and rules here. Why not follow the rules of a well established and battle tested stats infra used by everyone i.e. vmstats? There is no sync flush and there are frequent async flushes. I think that is what Jesper wants as well. Shakeel