From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-yb1-f200.google.com (mail-yb1-f200.google.com [209.85.219.200]) by kanga.kvack.org (Postfix) with ESMTP id DCC026B02A7 for ; Mon, 5 Nov 2018 21:28:04 -0500 (EST) Received: by mail-yb1-f200.google.com with SMTP id g14-v6so361403ybf.12 for ; Mon, 05 Nov 2018 18:28:04 -0800 (PST) Received: from aserp2120.oracle.com (aserp2120.oracle.com. [141.146.126.78]) by mx.google.com with ESMTPS id e195-v6si29735138ywa.54.2018.11.05.18.28.03 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 05 Nov 2018 18:28:03 -0800 (PST) Date: Mon, 5 Nov 2018 18:27:47 -0800 From: Daniel Jordan Subject: Re: [RFC PATCH v4 01/13] ktask: add documentation Message-ID: <20181106022747.dmtq24pvulcnv3lc@ca-dmjordan1.us.oracle.com> References: <20181105165558.11698-1-daniel.m.jordan@oracle.com> <20181105165558.11698-2-daniel.m.jordan@oracle.com> <7693f8a2-e180-520a-0d07-cc3090d2139f@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7693f8a2-e180-520a-0d07-cc3090d2139f@infradead.org> Sender: owner-linux-mm@kvack.org List-ID: To: Randy Dunlap Cc: Daniel Jordan , linux-mm@kvack.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, aarcange@redhat.com, aaron.lu@intel.com, akpm@linux-foundation.org, alex.williamson@redhat.com, bsd@redhat.com, darrick.wong@oracle.com, dave.hansen@linux.intel.com, jgg@mellanox.com, jwadams@google.com, jiangshanlai@gmail.com, mhocko@kernel.org, mike.kravetz@oracle.com, Pavel.Tatashin@microsoft.com, prasad.singamsetty@oracle.com, steven.sistare@oracle.com, tim.c.chen@intel.com, tj@kernel.org, vbabka@suse.cz On Mon, Nov 05, 2018 at 01:19:50PM -0800, Randy Dunlap wrote: > On 11/5/18 8:55 AM, Daniel Jordan wrote: > > Hi, > > > +Resource Limits > > +=============== > > + > > +ktask has resource limits on the number of work items it sends to workqueue. > > to a workqueue. > or: to workqueues. Ok, I'll do "to workqueues" since ktask uses two internally (NUMA-aware and non-NUMA-aware). > > > +In ktask, a workqueue item is a thread that runs chunks of the task until the > > +task is finished. > > + > > +These limits support the different ways ktask uses workqueues: > > + - ktask_run to run threads on the calling thread's node. > > + - ktask_run_numa to run threads on the node(s) specified. > > + - ktask_run_numa with nid=NUMA_NO_NODE to run threads on any node in the > > + system. > > + > > +To support these different ways of queueing work while maintaining an efficient > > +concurrency level, we need both system-wide and per-node limits on the number > > I would prefer to refer to ktask as ktask instead of "we", so > s/we need/ktask needs/ Good idea, I'll change it. > > +of threads. Without per-node limits, a node might become oversubscribed > > +despite ktask staying within the system-wide limit, and without a system-wide > > +limit, we can't properly account for work that can run on any node. > > s/we/ktask/ Ok. > > + > > +The system-wide limit is based on the total number of CPUs, and the per-node > > +limit on the CPU count for each node. A per-node work item counts against the > > +system-wide limit. Workqueue's max_active can't accommodate both types of > > +limit, no matter how many workqueues are used, so ktask implements its own. > > + > > +If a per-node limit is reached, the work item is allowed to run anywhere on the > > +machine to avoid overwhelming the node. If the global limit is also reached, > > +ktask won't queue additional work items until we fall below the limit again. > > s/we fall/ktask falls/ > or s/we fall/it falls/ 'ktask.' Will change. > > + > > +These limits apply only to workqueue items--that is, helper threads beyond the > > +one starting the task. That way, one thread per task is always allowed to run. > > > thanks. Appreciate the feedback!