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Date: Mon, 9 Mar 2026 10:21:18 +0100 From: Roger Pau =?utf-8?B?TW9ubsOp?= To: Jan Beulich Cc: "xen-devel@lists.xenproject.org" , Andrew Cooper , Julien Grall , Stefano Stabellini , Anthony PERARD , Michal Orzel Subject: Re: [PATCH] core-parking: shrink and relocate core_parking_cpunum[] Message-ID: References: <8b7e5cf6-e259-46a1-9af9-8b75242d9c7c@suse.com> Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <8b7e5cf6-e259-46a1-9af9-8b75242d9c7c@suse.com> X-ClientProxiedBy: MA3P292CA0014.ESPP292.PROD.OUTLOOK.COM (2603:10a6:250:2c::15) To CH7PR03MB7860.namprd03.prod.outlook.com (2603:10b6:610:24e::14) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: BY1PR03MB7875:EE_|LV4PR03MB8284:EE_ X-MS-Office365-Filtering-Correlation-Id: 634c1685-9318-4a57-349a-08de7dbd5b89 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|366016|1800799024|376014|7053199007; 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Use the smallest possible type. > >> > >> Further the array having all fields set to -1 is actually useless. Nothing > >> relies on it, and core_parking_remove() doesn't restore the sentinel for > >> vacated slots. Drop the initializers, moving the array to .bss. > >> > >> Finally take the opportunity and update an adjacent variable's type, where > >> a fixed-width type was pretty clearly inappropriate to use. > >> > >> Signed-off-by: Jan Beulich > >> --- > >> I assume there is a reason this is acting (mostly) as a LIFO. Else a > >> simple cpumask_t would suffice. > >> > >> An alternative would be to use the new BRK allocator, at least for NR_CPUS > >> above a certain threshold. > > > > Can't we just allocate this memory using xvzalloc_array()? If we do > > care about it being too big certainly allocating only when needed, and > > based on the number of possible CPUs on the system would be much > > better than playing games with the array type? > > Hmm, yes, how did it not occur to me to dynamically allocate the array? > It can't be used ahead of core_parking_init(). (Not shrinking the array > element type will still be a little wasteful, but perhaps that's > acceptable to keep the code simple.) We don't shrink other similar element types based on the supported CPU count. Iff we ever wanted to do this (which I'm not sure) we should introduce a new typedef that generalizes the optimization rather than open coding it (ie: cpu_id_t or similar?) Thanks, Roger.