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client-ip=165.204.84.17; helo=SATLEXMB04.amd.com; pr=C Received: from SATLEXMB04.amd.com (165.204.84.17) by SJ1PEPF000026C5.mail.protection.outlook.com (10.167.244.102) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.20.8511.15 via Frontend Transport; Tue, 4 Mar 2025 05:31:25 +0000 Received: from [10.136.44.144] (10.180.168.240) by SATLEXMB04.amd.com (10.181.40.145) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256) id 15.1.2507.39; Mon, 3 Mar 2025 23:31:09 -0600 Message-ID: <1a969884-8245-4bea-b4cc-d1727348bf50@amd.com> Date: Tue, 4 Mar 2025 11:01:07 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] pipe_read: don't wake up the writer if the pipe is still full To: Linus Torvalds , Oleg Nesterov CC: Mateusz Guzik , "Sapkal, Swapnil" , Manfred Spraul , Christian Brauner , David Howells , WangYuli , , , "Shenoy, Gautham Ranjal" , , 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> Content-Language: en-US From: K Prateek Nayak In-Reply-To: Content-Type: text/plain; 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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 04 Mar 2025 05:31:25.9970 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 66b20459-02a1-4848-5217-08dd5addcee2 X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[SATLEXMB04.amd.com] X-MS-Exchange-CrossTenant-AuthSource: SJ1PEPF000026C5.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: PH0PR12MB7885 Hello Linus, On 3/4/2025 2:16 AM, 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. > > ENTIRELY UNTESTED, but it seems to generate ok code. It might even > generate better code than what we have now. With the patch on top of commit aaec5a95d596 ("pipe_read: don't wake up the writer if the pipe is still full"), we've not seen any hangs yet with a few thousand iterations of short loops, and a few hundred iterations of larger loop sizes with hackbench. If you can provide you S-o-b, we can send out an official patch with a commit log. We'll wait for Oleg's response in case he has any concerns. > > Linus -- Thanks and Regards, Prateek