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Message-Id: <20240628122029.ed510073c534b739ee385521@linux-foundation.org> In-Reply-To: <20240628094944.QwcHkf8J@linutronix.de> References: <20240621102750.oH9p1FQq@linutronix.de> <20240628094944.QwcHkf8J@linutronix.de> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 5392DC0005 X-Stat-Signature: 3yoy85mu5yz4pia3mbzkkyiufcmubrpa X-HE-Tag: 1719602432-811418 X-HE-Meta: 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 U+F1vUsh yUciCNgDa6PzgNMoOri7y+n+TrfpI8GyOBqKYPs/Se9GB6uXBxna/aotQnzEg29hL8+Aa5Mq91LzRl0vjvHYVN2SFXQh9/LGHd2WSOd48dkWiNNDZyb1i/acs2J3yXILSvHjX++UQXUUAK89vo+46B/HzeHXSG+wimf8+quSghwcYjMDFzJTf330oCZnD3rIaVk8XFJnMTUGsI1xTA8SFujRBZgmKaXqTuZk/v54SNewMZNviQ6et8Ij0TQpwvhEec42cBFH+Q87l9kvt6xBmNej5jrrZ1e0eqC5ViUozYulLBO6PH2wIHtWqV7KX130UVNyT3kJqRcf/kkQ= 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 Fri, 28 Jun 2024 11:49:44 +0200 Sebastian Andrzej Siewior wrote: > On 2024-06-21 12:27:52 [+0200], To linux-mm@kvack.org wrote: > > The alloc_tag member has been added to task_struct at the very > > beginning. This is a pointer and on 64bit architectures it forces 4 byte > > padding after `ptrace' and then forcing another another 4 byte padding > > after `on_cpu'. A few members later, `se' requires a cacheline aligned > > due to struct sched_avg resulting in 52 hole before `se'. > > > > This is the case on 64bit-SMP architectures. > > The 52 byte hole can be avoided by moving alloc_tag away where it > > currently resides. > > > > Move alloc_tag to the end of task_struct. There is likely a hole before > > `thread' due to its alignment requirement and the previous members are > > likely to be already pointer-aligned. > > > > Fixes: 22d407b164ff7 ("lib: add allocation tagging support for memory allocation profiling") > > Signed-off-by: Sebastian Andrzej Siewior > > Could we please get this merged and worry about possible performance > regression later? Or once there is a test case or an idea where this > pointer might fit better but clearly the current situation is worse. > All in favor of saving 56 bytes from the task_struct, but we can do that by moving various things around. Was alloc_tag the best choice?