linux-kernel - Re: [PATCH v1 09/11] x86/mm/pat: remove MEMTYPE_*

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Message-ID: <fe80481f-6fa9-4148-90b2-65734ef259ed@lucifer.local>
Date: Mon, 28 Apr 2025 21:23:00 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org, x86@...nel.org,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-trace-kernel@...r.kernel.org,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>, "H. Peter Anvin" <hpa@...or.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tursulin@...ulin.net>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>,
        Pedro Falcato <pfalcato@...e.de>, Peter Xu <peterx@...hat.com>
Subject: Re: [PATCH v1 09/11] x86/mm/pat: remove MEMTYPE_*_MATCH

On Fri, Apr 25, 2025 at 10:17:13AM +0200, David Hildenbrand wrote:
> The "memramp() shrinking" scenario no longer applies, so let's remove
> that now-unnecessary handling.

I wonder if we could remove even more of the code here given the
simplifications here? But not a big deal.

>
> Signed-off-by: David Hildenbrand <david@...hat.com>

More lovely removal...

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>

> ---
>  arch/x86/mm/pat/memtype_interval.c | 44 ++++--------------------------
>  1 file changed, 6 insertions(+), 38 deletions(-)
>
> diff --git a/arch/x86/mm/pat/memtype_interval.c b/arch/x86/mm/pat/memtype_interval.c
> index 645613d59942a..9d03f0dbc4715 100644
> --- a/arch/x86/mm/pat/memtype_interval.c
> +++ b/arch/x86/mm/pat/memtype_interval.c
> @@ -49,26 +49,15 @@ INTERVAL_TREE_DEFINE(struct memtype, rb, u64, subtree_max_end,
>
>  static struct rb_root_cached memtype_rbroot = RB_ROOT_CACHED;
>
> -enum {
> -	MEMTYPE_EXACT_MATCH	= 0,
> -	MEMTYPE_END_MATCH	= 1
> -};
> -
> -static struct memtype *memtype_match(u64 start, u64 end, int match_type)
> +static struct memtype *memtype_match(u64 start, u64 end)
>  {
>  	struct memtype *entry_match;
>
>  	entry_match = interval_iter_first(&memtype_rbroot, start, end-1);
>
>  	while (entry_match != NULL && entry_match->start < end) {
> -		if ((match_type == MEMTYPE_EXACT_MATCH) &&
> -		    (entry_match->start == start) && (entry_match->end == end))
> -			return entry_match;
> -
> -		if ((match_type == MEMTYPE_END_MATCH) &&
> -		    (entry_match->start < start) && (entry_match->end == end))
> +		if (entry_match->start == start && entry_match->end == end)
>  			return entry_match;
> -
>  		entry_match = interval_iter_next(entry_match, start, end-1);
>  	}
>
> @@ -132,32 +121,11 @@ struct memtype *memtype_erase(u64 start, u64 end)
>  {
>  	struct memtype *entry_old;
>
> -	/*
> -	 * Since the memtype_rbroot tree allows overlapping ranges,
> -	 * memtype_erase() checks with EXACT_MATCH first, i.e. free
> -	 * a whole node for the munmap case.  If no such entry is found,
> -	 * it then checks with END_MATCH, i.e. shrink the size of a node
> -	 * from the end for the mremap case.
> -	 */
> -	entry_old = memtype_match(start, end, MEMTYPE_EXACT_MATCH);
> -	if (!entry_old) {
> -		entry_old = memtype_match(start, end, MEMTYPE_END_MATCH);
> -		if (!entry_old)
> -			return ERR_PTR(-EINVAL);
> -	}
> -
> -	if (entry_old->start == start) {
> -		/* munmap: erase this node */
> -		interval_remove(entry_old, &memtype_rbroot);
> -	} else {
> -		/* mremap: update the end value of this node */
> -		interval_remove(entry_old, &memtype_rbroot);
> -		entry_old->end = start;
> -		interval_insert(entry_old, &memtype_rbroot);
> -
> -		return NULL;
> -	}
> +	entry_old = memtype_match(start, end);
> +	if (!entry_old)
> +		return ERR_PTR(-EINVAL);
>
> +	interval_remove(entry_old, &memtype_rbroot);
>  	return entry_old;
>  }
>
> --
> 2.49.0
>