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b=Fmr+C0meO0phtojZmaOaCckdbakce0kBzbZr1lRTpGTj6TeFVjhQ2yQmuGX7Ybdl3Q03mynQfH1EYTa67VtvWnmr100hAMS+eN2RsN38brjhv+S4xv3gPufyGvJ0pnrkgx2eKCniwd22Cgm5aJGnlJ2xbI1Jq13Nrfyf7GjWQuM= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=prevas.dk; Received: from VI1PR10MB2477.EURPRD10.PROD.OUTLOOK.COM (2603:10a6:803:87::20) by DB5PR10MB7752.EURPRD10.PROD.OUTLOOK.COM (2603:10a6:10:4aa::11) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.8511.17; Wed, 5 Mar 2025 15:31:48 +0000 Received: from VI1PR10MB2477.EURPRD10.PROD.OUTLOOK.COM ([fe80::4e8:da5:4265:ce59]) by VI1PR10MB2477.EURPRD10.PROD.OUTLOOK.COM ([fe80::4e8:da5:4265:ce59%6]) with mapi id 15.20.8466.028; Wed, 5 Mar 2025 15:31:48 +0000 From: Rasmus Villemoes To: Linus Torvalds Cc: Oleg Nesterov , Mateusz Guzik , K Prateek Nayak , "Sapkal, Swapnil" , Manfred Spraul , Christian Brauner , David Howells , WangYuli , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, "Shenoy, Gautham Ranjal" , Neeraj.Upadhyay@amd.com, Ananth.narayan@amd.com, Matthew Wilcox Subject: Re: [PATCH] pipe_read: don't wake up the writer if the pipe is still full In-Reply-To: (Linus Torvalds's message of "Mon, 3 Mar 2025 10:46:10 -1000") References: <20250228143049.GA17761@redhat.com> <20250228163347.GB17761@redhat.com> <03a1f4af-47e0-459d-b2bf-9f65536fc2ab@amd.com> <741fe214-d534-4484-9cf3-122aabe6281e@amd.com> <3jnnhipk2at3f7r23qb7fvznqg6dqw4rfrhajc7h6j2nu7twi2@wc3g5sdlfewt> <20250303202735.GD9870@redhat.com> Date: Wed, 05 Mar 2025 16:31:45 +0100 Message-ID: <87h6475w9q.fsf@prevas.dk> User-Agent: Gnus/5.13 (Gnus v5.13) Content-Type: text/plain X-ClientProxiedBy: BE1P281CA0048.DEUP281.PROD.OUTLOOK.COM (2603:10a6:b10:23::20) To VI1PR10MB2477.EURPRD10.PROD.OUTLOOK.COM (2603:10a6:803:87::20) Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: VI1PR10MB2477:EE_|DB5PR10MB7752:EE_ X-MS-Office365-Filtering-Correlation-Id: a0f80764-2173-4675-d3af-08dd5bfad7f8 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0;ARA:13230040|52116014|7416014|376014|366016|1800799024|7053199007|38350700014; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?kBYENrOLr17CukacpeeMvz8Nh3L7AN4EJOSMGxFaTseg8jMlOVHUE/kvM5uH?= =?us-ascii?Q?dV9G+n4xaapca/y9Lv2DVmRaCwLk0Es4xVClBVA7ynY1IuzO5mQo5KZEk096?= =?us-ascii?Q?d0p4gEpWICkwahDVvEFI1DCcZCrk12WDCo/T5THOIFwQzGdhFREH+NnNri7r?= =?us-ascii?Q?2hIaCeN25hA5zo3gCUZksW2bhSV3WrqA2AzbBdNVsJz7wqMRlB8dqP84EMwp?= =?us-ascii?Q?ck1DC3AEmEJd29YvMR4Kq3swi9i+bJfe9oGe20kojPwQfBrz4OuFcQ9LaYBt?= =?us-ascii?Q?/l1bgGcEsN0f63c3vm7d96EAVpA9tvLoMusWSaoTUcqLq8U9KH9ZMzL0k8dj?= =?us-ascii?Q?aedsRspdOKCph5KGO0RLoh317wM+OhHkMb9/1i6vWksdzFaC6EpLaigp72nL?= =?us-ascii?Q?VY3pIi79HtI5ymuhrYUh44r1YXTvVIBGGq7Vf2XXEPIO8UFFJvK/Oywo9cn/?= =?us-ascii?Q?SVzW5kRbyagUzRh3wmRImulTOyK9ThTS3Y9aKrhZwxMTJ7z5c4vY00pZgl/I?= =?us-ascii?Q?x+ViLKgv8PnjPRfY9dqrwWNRIDwD6bX/qeuqi767kFrGRxf9yfQNa7MgDLSu?= =?us-ascii?Q?3KomE9rMVxmI34xcKuyPxhXVQ0x5+vExjM3qBWeZc0Ia6U8rKV9jxR3hXo2N?= =?us-ascii?Q?A19eQpwSjvWgNE+vsffj55AuBCst1wurjS6FS3bwyTRNFR238er0Tc/Pyvnx?= =?us-ascii?Q?sJFXd9+TQxpby2bLQLuql109miHH7b8ilTORCP/AVmVdO6iijPamlJsd41Un?= =?us-ascii?Q?L7EXsPr4151B5TGEsm70/5wlrJdwdcS6dYh91Wd/j0FrVTfuJp//Ux3byt6T?= =?us-ascii?Q?RG3Psbmds0mwvuJycMp3yaRRp3ZdlXnzpFuLjWyN4E4o1Nl6LZJmw8bHfD3U?= =?us-ascii?Q?xOR9VAZUAq+oIsw54rwlwA4BGPrEvjzvc3V2w4ky2G+FkhANHSvKvHSFyj6A?= =?us-ascii?Q?/hx1fUwDzSfN2jnc9tA2u0PN/hgIVnMLXpZQlhdj1tuapbUJZsDXPOrQIVyz?= =?us-ascii?Q?eO2LbZRvk7G5tV1HtuzCsCR6xEsDGalMMtgehfe2GA2qtyQ87IGWmbngNyPc?= =?us-ascii?Q?9gl0tZpac9ole1xokBcsMx3WcQQAQGEOwoOFJI3qUWY5ZLpxKwPuSzKBajOJ?= =?us-ascii?Q?biPH2SHE3joazilkhZoYOe/haF7cEzyUamwkFmwAtyDOldVgwv1UeR13ww1z?= =?us-ascii?Q?qznw8ApaepLUQdE4WXjMcU626CRoUL8kzfIXnR7htkjHQqZ/xDanwCpaopmI?= =?us-ascii?Q?03pbj+gYPrAgrEP9CQkLItowGDvxhirEutLPM94twu72hp8SL8Y4wpGdSuuL?= =?us-ascii?Q?6sHnuXjJ3q1Ov8NvQ+bsbwzxXI7eRPtWxgemmE5yzosOho1VYOf8hGqomxMw?= =?us-ascii?Q?vfTRVBgLkoky3vFvpN4NcKtY7SEjWT4E9TsbFyD7MlvWj2/EtTdocHYbXlHP?= =?us-ascii?Q?TpD9MY7boXZ5nx2+TfnO6VW9kJgfwCAT5k0lBW92z20vFe2n2uaftZTImmr1?= =?us-ascii?Q?k9ZHbMa8zThoyRFb3HUKRm9tWfK2DkPcAn44nq/Ibt268ElZVGZ4pg6X3YUY?= =?us-ascii?Q?i2+q1QH8jQDHhN8Yhwwj0Khrygr+fYBa7mV26xSsrP8xF5jVEi2U3JkmRdyi?= =?us-ascii?Q?0w=3D=3D?= X-OriginatorOrg: prevas.dk X-MS-Exchange-CrossTenant-Network-Message-Id: a0f80764-2173-4675-d3af-08dd5bfad7f8 X-MS-Exchange-CrossTenant-AuthSource: VI1PR10MB2477.EURPRD10.PROD.OUTLOOK.COM X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 05 Mar 2025 15:31:48.3756 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: d350cf71-778d-4780-88f5-071a4cb1ed61 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: gu47hBGzOrWMNxzwWXmLPPh5chlBnWDNE5SGYGh/4GIjpdOHAh048xoMiBZ5Wo82jwhHBDTVSFhpdtXBbV1zSX5SZN0/lSAb4WCphdtDLAM= X-MS-Exchange-Transport-CrossTenantHeadersStamped: DB5PR10MB7752 On Mon, Mar 03 2025, Linus Torvalds wrote: > On Mon, 3 Mar 2025 at 10:28, Oleg Nesterov wrote: >> >> Stupid question... but do we really need to change the code which update >> tail/head if we pack them into a single word? > > No. It's only the READ_ONCE() parts that need changing. > > See this suggested patch, which does something very similar to what > you were thinking of. > > +/* > + * We have to declare this outside 'struct pipe_inode_info', > + * but then we can't use 'union pipe_index' for an anonymous > + * union, so we end up having to duplicate this declaration > + * below. Annoying. > + */ > +union pipe_index { > + unsigned long head_tail; > + struct { > + pipe_index_t head; > + pipe_index_t tail; > + }; > +}; > + -fms-extensions ? Willy wanted to add that for use in mm/ some years ago [*], and it has come up a few other times as well. [*] https://lore.kernel.org/lkml/20180419152817.GD25406@bombadil.infradead.org/ Rasmus