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From: Shakeel Butt To: Johannes Weiner Cc: Yosry Ahmed , Andrew Morton , Michal Hocko , Roman Gushchin , Muchun Song , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 5/7] memcg: pr_warn_once for unexpected events and stats Message-ID: <5eh7nwj6tnl76bkwnksgbb63mjmvf3rzlaevepcxecl3xhmkc7@hbcmkhseaoky> References: <20240427003733.3898961-1-shakeel.butt@linux.dev> <20240427003733.3898961-6-shakeel.butt@linux.dev> <20240427142234.GA1155473@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20240427142234.GA1155473@cmpxchg.org> X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: D26F2160016 X-Stat-Signature: moarokicmxnxdkkyomdjmfn7swi3ycp5 X-HE-Tag: 1714420454-555187 X-HE-Meta: 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 +LhTW2AH 0ue3GEJsmuVCQP+Yl6GGWKGKvwmKLSTdhIEjhyHJpvJvn71wr3XhPJ2CRhFQ9Tn1Cz5C5UVRrCpaXh6/PYn/9EaJMwa17Wsa3XOueaIaN0uNO1Bv2P9UeZZOZ9FHXcI2noPoJbcIz9JHANVhrWq1ZSpvvhaod43B15bPM X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, 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, Apr 27, 2024 at 10:22:34AM -0400, Johannes Weiner wrote: > On Fri, Apr 26, 2024 at 06:18:13PM -0700, Shakeel Butt wrote: > > On Fri, Apr 26, 2024 at 05:58:16PM -0700, Yosry Ahmed wrote: > > > On Fri, Apr 26, 2024 at 5:38 PM Shakeel Butt wrote: [...] > > > > > > Can we make these more compact by using WARN_ON_ONCE() instead: > > > > > > if (WARN_ON_ONCE(i < 0)) > > > return 0; > > > > > > I guess the advantage of using pr_warn_once() is that we get to print > > > the exact stat index, but the stack trace from WARN_ON_ONCE() should > > > make it obvious in most cases AFAICT. > > if (WARN_ONCE(i < 0, "stat item %d not in memcg_node_stat_items\n", i)) > return 0; > > should work? > > > > No strong opinions either way. > > > > One reason I used pr_warn_once() over WARN_ON_ONCE() is the syzbot > > trigger. No need to trip the bot over this error condition. > > The warn splat is definitely quite verbose. But I think that would > only be annoying initially, in case a site was missed. Down the line, > it seems helpful to have this stand out to somebody who is trying to > add a new cgroup stat and forgets to update the right enums. Sounds good to me. I will change it to WARN_ONCE().