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[96.255.20.138]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-8942e6ad6ffsm110202716d6.27.2026.01.20.11.53.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 Jan 2026 11:53:22 -0800 (PST) Date: Tue, 20 Jan 2026 14:52:50 -0500 From: Gregory Price To: David Laight Cc: Li Zhe , akpm@linux-foundation.org, ankur.a.arora@oracle.com, dan.j.williams@intel.com, dave@stgolabs.net, david@kernel.org, fvdl@google.com, joao.m.martins@oracle.com, jonathan.cameron@huawei.com, linux-cxl@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mhocko@suse.com, mjguzik@gmail.com, muchun.song@linux.dev, osalvador@suse.de, raghavendra.kt@amd.com, wangzhou1@hisilicon.com, zhanjie9@hisilicon.com Subject: Re: [PATCH v2 0/8] Introduce a huge-page pre-zeroing mechanism Message-ID: References: <20260120094744.5d92e34a@pumpkin> <20260120103949.7673-1-lizhe.67@bytedance.com> <20260120193027.3d160211@pumpkin> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260120193027.3d160211@pumpkin> X-Stat-Signature: 7mi6hudapr3kezem5rythdc39z3tocd1 X-Rspam-User: X-Rspamd-Queue-Id: 8421B120002 X-Rspamd-Server: rspam08 X-HE-Tag: 1768938804-124137 X-HE-Meta: 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 brc2zVHM 3CnQYA8ab8jH4bfgwZh/nXhPWmc2i6Ju9wXNEiBTgiCGriniPO13RIP4/6L8PRkpEvjiTiIOnISbRw29Tqt3ikmDQKwPyt7JYNfyaMWU9t5hecCfHvl75cEB+js/GV6ysY585rlYUT944FFbkB1NpeHjDZ8SSqneXcuoFQiSzUVLUckl8uyDSHa3cUkX6/qcuT1cHWXC3acBCxrER071/v0LOIgSaiNdt4cNStgFn7Bx7ej64+s1iOcg3NwPtTH8u58Cxy4p+BFTa9ppbcC+8x93E2aC+KZEYBsfF6ngfFy09YcK5qYZUptB1o1YNswwFHkaGJljWvCibeULe4T6YVqVCU7g6ESCRh9fmPGIPxnrVcsorWSLfommIdHJzEIK0ymUuLVn7BA3MUplA4ZOms1z1xQ== 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 Tue, Jan 20, 2026 at 07:30:27PM +0000, David Laight wrote: > > /* Run programs in serial */ > > sh: program_a && program_b > > > > in zero_on_alloc(): > > program_a eats zero(10) cost on startup > > program_b eats zero(5) cost on startup > > Overall zero(15) cost to start program_b > > > > in zero_on_free() > > program_a eats zero(10) cost on startup > > Do you get that cost? - wont all the unused memory be zeros. > If program_a was the first to access, wouldn't it have had to zero it? > > But just trivially, starting from the base case of no pages being > > zeroed, you're just injecting an additional zero(X) cost if program_a() > > consumes more hugepages than program_b(). > > I'd consider a different test: > for c in $(jot 1 1000); do program_a; done > > Regardless of whether you zero on alloc or free all the zeroing is in line. > Move it to a low priority thread (that uses a non-aggressive loop) and > there will be reasonable chance of there being pre-zeroed pages available. > (Most DMA is far too aggressive...) > > If you zero on free it might also be a waste of time. > Maybe the memory is next used to read data from a disk file. > Right, both points here being that it's heuristic-y, it only applies in certain scenarios and trying to optimize for one probably hurts another. ~Gregory