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Message-ID: <acac6cc8-fd83-4541-8310-63f37cd41fa6@intel.com>
Date: Thu, 15 Feb 2024 16:30:46 -0800
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Subject: Re: [RFC PATCH 1/8] mm: Switch mm->get_unmapped_area() to a flag
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To: Rick Edgecombe <rick.p.edgecombe@intel.com>, 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 <dave.hansen@intel.com>
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In-Reply-To: <20240215231332.1556787-2-rick.p.edgecombe@intel.com>
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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 <dave.hansen@linux.intel.com>