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X-IronPort-AV: E=McAfee;i="6600,9927,10985"; a="5133561" X-IronPort-AV: E=Sophos;i="6.06,163,1705392000"; d="scan'208";a="5133561" Received: from fmviesa001.fm.intel.com ([10.60.135.141]) by fmvoesa107.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Feb 2024 16:30:46 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.06,163,1705392000"; d="scan'208";a="34753302" Received: from jmjohns4-mobl1.amr.corp.intel.com (HELO [10.209.57.138]) ([10.209.57.138]) by smtpauth.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Feb 2024 16:30:45 -0800 Message-ID: Date: Thu, 15 Feb 2024 16:30:46 -0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH 1/8] mm: Switch mm->get_unmapped_area() to a flag Content-Language: en-US To: Rick Edgecombe , Liam.Howlett@oracle.com, akpm@linux-foundation.org, debug@rivosinc.com, broonie@kernel.org, kirill.shutemov@linux.intel.com, keescook@chromium.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, luto@kernel.org, peterz@infradead.org, hpa@zytor.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20240215231332.1556787-1-rick.p.edgecombe@intel.com> <20240215231332.1556787-2-rick.p.edgecombe@intel.com> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 565B140016 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: 3kfe1qrs59u1yoegds4mm1mmkcny47kd X-HE-Tag: 1708043448-831494 X-HE-Meta: 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 EaA24wu0 dFnnq5HzwnHtunveCoD6v7sZZqu2x7a3ePVuTCQoeDsi295w1oGqVK2qY0jaNNHqVvL9VmUS+0o43okHYaQB8Zd4s0qmAx331t3UqUruoXpI7x/S4r0IrWRsZDxXEeJLl5X+Am68wy/fXcro6eqYn4QRD7wD53Rptu3GW/7UL32Nba6HBeQ/lmbBfxpBMmavKvtXx4czJQTAb0c9TMvQVJRLkFg== 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 2/15/24 15:13, Rick Edgecombe wrote: > The mm_struct contains a function pointer *get_unmapped_area(), which > is set to either arch_get_unmapped_area() or > arch_get_unmapped_area_topdown() during the initialization of the mm. > > Since the function pointer only ever points to two functions that are named > the same across all arch's, a function pointer is not really required. In > addition future changes will want to add versions of the functions that > take additional arguments. So to save a pointers worth of bytes in > mm_struct, and prevent adding additional function pointers to mm_struct in > future changes, remove it and keep the information about which > get_unmapped_area() to use in a flag. Indirect calls are just all kinds of evil, especially when Spectre-v2 is in play. This is a really good idea. Acked-by: Dave Hansen