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Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1fflqe-0004mL-Ov; Wed, 18 Jul 2018 12:46:29 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 2E0D120275F38; Wed, 18 Jul 2018 14:46:27 +0200 (CEST) Date: Wed, 18 Jul 2018 14:46:27 +0200 From: Peter Zijlstra To: Johannes Weiner Cc: Ingo Molnar , Andrew Morton , Linus Torvalds , Tejun Heo , Suren Baghdasaryan , Vinayak Menon , Christopher Lameter , Mike Galbraith , Shakeel Butt , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH 08/10] psi: pressure stall information for CPU, memory, and IO Message-ID: <20180718124627.GD2476@hirez.programming.kicks-ass.net> References: <20180712172942.10094-1-hannes@cmpxchg.org> <20180712172942.10094-9-hannes@cmpxchg.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180712172942.10094-9-hannes@cmpxchg.org> User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 12, 2018 at 01:29:40PM -0400, Johannes Weiner wrote: > +static inline void psi_enqueue(struct task_struct *p, u64 now, bool wakeup) > +{ > + int clear = 0, set = TSK_RUNNING; > + > + if (psi_disabled) > + return; > + > + if (!wakeup || p->sched_psi_wake_requeue) { > + if (p->flags & PF_MEMSTALL) > + set |= TSK_MEMSTALL; > + if (p->sched_psi_wake_requeue) > + p->sched_psi_wake_requeue = 0; > + } else { > + if (p->in_iowait) > + clear |= TSK_IOWAIT; > + } > + > + psi_task_change(p, now, clear, set); > +} > + > +static inline void psi_dequeue(struct task_struct *p, u64 now, bool sleep) > +{ > + int clear = TSK_RUNNING, set = 0; > + > + if (psi_disabled) > + return; > + > + if (!sleep) { > + if (p->flags & PF_MEMSTALL) > + clear |= TSK_MEMSTALL; > + } else { > + if (p->in_iowait) > + set |= TSK_IOWAIT; > + } > + > + psi_task_change(p, now, clear, set); > +} > +/** > + * psi_memstall_enter - mark the beginning of a memory stall section > + * @flags: flags to handle nested sections > + * > + * Marks the calling task as being stalled due to a lack of memory, > + * such as waiting for a refault or performing reclaim. > + */ > +void psi_memstall_enter(unsigned long *flags) > +{ > + struct rq_flags rf; > + struct rq *rq; > + > + if (psi_disabled) > + return; > + > + *flags = current->flags & PF_MEMSTALL; > + if (*flags) > + return; > + /* > + * PF_MEMSTALL setting & accounting needs to be atomic wrt > + * changes to the task's scheduling state, otherwise we can > + * race with CPU migration. > + */ > + rq = this_rq_lock_irq(&rf); > + > + update_rq_clock(rq); > + > + current->flags |= PF_MEMSTALL; > + psi_task_change(current, rq_clock(rq), 0, TSK_MEMSTALL); > + > + rq_unlock_irq(rq, &rf); > +} I'm confused by this whole MEMSTALL thing... I thought the idea was to account the time we were _blocked_ because of memstall, but you seem to count the time we're _running_ with PF_MEMSTALL. And esp. the wait_on_page_bit_common caller seems performance sensitive, and the above function is quite expensive.