linux-kernel - Re: [RFC PATCH 1/8] mm: Switch mm->get_unmapped

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Date: Thu, 15 Feb 2024 21:15:23 -0500
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: Dave Hansen <dave.hansen@...el.com>
Cc: Rick Edgecombe <rick.p.edgecombe@...el.com>, akpm@...ux-foundation.org,
        debug@...osinc.com, broonie@...nel.org,
        kirill.shutemov@...ux.intel.com, keescook@...omium.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, luto@...nel.org,
        peterz@...radead.org, hpa@...or.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/8] mm: Switch mm->get_unmapped_area() to a flag

* Dave Hansen <dave.hansen@...el.com> [240215 19:30]:
> 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@...ux.intel.com>

Yes, this change can stand on its own I believe.

Acked-by: Liam R. Howlett <Liam.Howlett@...cle.com>