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Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1uNSLd-000000057xs-18V4; Fri, 06 Jun 2025 08:22:45 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id B1DA8300348; Fri, 6 Jun 2025 10:22:44 +0200 (CEST) Date: Fri, 6 Jun 2025 10:22:44 +0200 From: Peter Zijlstra To: Zihuan Zhang Cc: rafael@kernel.org, len.brown@intel.com, pavel@kernel.org, kees@kernel.org, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, akpm@linux-foundation.org, david@redhat.com, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [RFC PATCH] PM: Optionally block user fork during freeze to improve performance Message-ID: <20250606082244.GL30486@noisy.programming.kicks-ass.net> References: <20250606062502.19607-1-zhangzihuan@kylinos.cn> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250606062502.19607-1-zhangzihuan@kylinos.cn> X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 63DEB10000C X-Stat-Signature: m1xktnxrs3gm3yjcsueicpt8xcrbqekc X-Rspam-User: X-HE-Tag: 1749198180-893625 X-HE-Meta: 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 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 Fri, Jun 06, 2025 at 02:25:02PM +0800, Zihuan Zhang wrote: > @@ -2596,6 +2597,11 @@ pid_t kernel_clone(struct kernel_clone_args *args) > trace = 0; > } > > +#ifdef CONFIG_PM_DISABLE_USER_FORK_DURING_FREEZE > + if (pm_should_block_fork() && !(current->flags & PF_KTHREAD)) > + return -EBUSY; > +#endif > + > p = copy_process(NULL, trace, NUMA_NO_NODE, args); > add_latent_entropy(); This isn't blocking fork(), this is failing fork(). Huge difference. Also problematic, because -EBUSY is not a recognised return value of fork(). As such, no existing software will adequately handle it.