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Wed, 09 Oct 2019 02:47:23 -0700 (PDT) Received: from pc636 ([37.139.158.167]) by smtp.gmail.com with ESMTPSA id d28sm361521lfq.88.2019.10.09.02.47.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 09 Oct 2019 02:47:22 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Wed, 9 Oct 2019 11:47:14 +0200 To: Daniel Wagner Cc: Uladzislau Rezki , Sebastian Andrzej Siewior , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org, Andrew Morton Subject: Re: [PATCH] mm: vmalloc: Use the vmap_area_lock to protect ne_fit_preload_node Message-ID: <20191009094714.GA7343@pc636> References: <20191004163042.jpiau6dlxqylbpfh@linutronix.de> <20191007083037.zu3n5gindvo7damg@beryllium.lan> <20191007105631.iau6zhxqjeuzajnt@linutronix.de> <20191007162330.GA26503@pc636> <20191007163443.6owts5jp2frum7cy@beryllium.lan> <20191007165611.GA26964@pc636> <20191007173644.hiiukrl2xryziro3@linutronix.de> <20191007214420.GA3212@pc636> <20191008160459.GA5487@pc636> <20191009060539.fmpqesc4wfisulrl@beryllium.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191009060539.fmpqesc4wfisulrl@beryllium.lan> User-Agent: Mutt/1.10.1 (2018-07-13) 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: Hello, Daniel. On Wed, Oct 09, 2019 at 08:05:39AM +0200, Daniel Wagner wrote: > On Tue, Oct 08, 2019 at 06:04:59PM +0200, Uladzislau Rezki wrote: > > > so, we do not guarantee, instead we minimize number of allocations > > > with GFP_NOWAIT flag. For example on my 4xCPUs i am not able to > > > even trigger the case when CPU is not preloaded. > > > > > > I can test it tomorrow on my 12xCPUs to see its behavior there. > > > > > Tested it on different systems. For example on my 8xCPUs system that > > runs PREEMPT kernel i see only few GFP_NOWAIT allocations, i.e. it > > happens when we land to another CPU that was not preloaded. > > > > I run the special test case that follows the preload pattern and path. > > So 20 "unbind" threads run it and each does 1000000 allocations. As a > > result only 3.5 times among 1000000, during splitting, CPU was not > > preloaded thus, GFP_NOWAIT was used to obtain an extra object. > > > > It is obvious that slightly modified approach still minimizes allocations > > in atomic context, so it can happen but the number is negligible and can > > be ignored, i think. > > Thanks for doing the tests. In this case I would suggest to get rid of > the preempt_disable() micro optimization, since there is almost no > gain in doing so. Do you send a patch? :) > I can do it, for sure, in case you do not mind, since it was your initiative. Otherwise you can upload v2. -- Vlad Rezki