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[87.161.166.165]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a5322ae43fsm1054006f8f.25.2025.06.06.00.20.28 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 06 Jun 2025 00:20:29 -0700 (PDT) Message-ID: <0030581f-d50a-48f4-86f5-58e7883f705d@redhat.com> Date: Fri, 6 Jun 2025 09:20:27 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH] PM: Optionally block user fork during freeze to improve performance To: Zihuan Zhang , rafael@kernel.org, len.brown@intel.com, pavel@kernel.org, kees@kernel.org, mingo@redhat.com, peterz@infradead.org, 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, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com Cc: linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <20250606062502.19607-1-zhangzihuan@kylinos.cn> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: 7B80740004 X-Stat-Signature: h7xtccc7qairfmqyqpqxiycjznn3sxwa X-Rspam-User: X-HE-Tag: 1749194433-128904 X-HE-Meta: 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 wIo+0S/e o/9mqoBBA02ueH/r3tA9AGNDxLVCcR+Jichf+HOcWcaJ0V/PE1YPZAnVPZPden162f3q04GcyZqFcJt2M6zzjDxHJazqXXO+ACXtja2f1gHRQ552aTeTl1qJi5F8mAE316LBnBheobdePeVMKhnaZ/TndJAAZ6bvWBrLH8pOCnHOrfv5ZJZNqz1e1XUbZ27TMI2Noz0oL7ilaE65dLCEJKpVWubQO8SJQ+DHPbWnspHML9SNTYHYm+rEqKZPvGmMdTZMSAPabL2QS4aYhQiVJygC4nCyapwobHfHTJcTt1YDGCkVLjjPN5TlHU1Q6eTE6oDR824s1R621gxvYNyGkVgQCd1Fi5Lt3futnPobrLoyZhu/mdRvO9HurikVyY4oPVvNhE7au9ghPnsTiEx7mewNdyO4vNUwAFSan3krxD6Duoi0= 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: Hi, On 06.06.25 08:25, Zihuan Zhang wrote: > Currently, the freezer traverses all tasks to freeze them during > system suspend or hibernation. If a user process forks during this > window, the new child may escape freezing and require a second > traversal or retry, adding non-trivial overhead. > > This patch introduces a CONFIG_PM_DISABLE_USER_FORK_DURING_FREEZE Not sure if a Kconfig is really the right choice here ... > option. When enabled, it prevents user processes from creating new > processes (via fork/clone) during the freezing period. This guarantees > a stable task list and avoids re-traversing the process list due to > late-created user tasks, thereby improving performance. Any performance numbers to back your claims? > > The restriction is only active during the window when the system is > freezing user tasks. Once all tasks are frozen, or if the system aborts > the suspend/hibernate process, the restriction is lifted. > No kernel threads are affected, and kernel_create_* functions remain > unrestricted. > > Signed-off-by: Zihuan Zhang > --- > include/linux/suspend.h | 8 ++++++++ > kernel/fork.c | 6 ++++++ > kernel/power/Kconfig | 10 ++++++++++ > kernel/power/main.c | 44 +++++++++++++++++++++++++++++++++++++++++ > kernel/power/power.h | 4 ++++ > kernel/power/process.c | 7 +++++++ > 6 files changed, 79 insertions(+) > > diff --git a/include/linux/suspend.h b/include/linux/suspend.h > index b1c76c8f2c82..2dd8b3eb50f0 100644 > --- a/include/linux/suspend.h > +++ b/include/linux/suspend.h > @@ -591,4 +591,12 @@ enum suspend_stat_step { > void dpm_save_failed_dev(const char *name); > void dpm_save_failed_step(enum suspend_stat_step step); > > +#ifdef CONFIG_PM_DISABLE_USER_FORK_DURING_FREEZE > +extern bool pm_block_user_fork; > +bool pm_should_block_fork(void); > +bool pm_freeze_process_in_progress(void); > +#else > +static inline bool pm_should_block_fork(void) { return false; }; > +static inline bool pm_freeze_process_in_progress(void) { return false; }; > +#endif /* CONFIG_PM_DISABLE_USER_FORK_DURING_FREEZE */ > #endif /* _LINUX_SUSPEND_H */ > diff --git a/kernel/fork.c b/kernel/fork.c > index 1ee8eb11f38b..b0bd0206b644 100644 > --- a/kernel/fork.c > +++ b/kernel/fork.c > @@ -105,6 +105,7 @@ > #include > #include > #include > +#include > > #include > #include > @@ -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 fork() is not documented to return EBUSY and for clone3() it's documented to only happen in specific cases. So user space is not prepared for that. -- Cheers, David / dhildenb