linux-kernel - Re: [PATCH 3/3 v3] mm/vmalloc: Cache the vmalloc memory info

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Message-ID: <20150825124655.GQ16853@twins.programming.kicks-ass.net>
Date:	Tue, 25 Aug 2015 14:46:55 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	George Spelvin <linux@...izon.com>, dave@...1.net,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux@...musvillemoes.dk, riel@...hat.com, rientjes@...gle.com,
	torvalds@...ux-foundation.org
Subject: Re: [PATCH 3/3 v3] mm/vmalloc: Cache the vmalloc memory info

On Sun, Aug 23, 2015 at 10:17:51AM +0200, Ingo Molnar wrote:
> +static u64 vmap_info_gen;
> +static u64 vmap_info_cache_gen;

> +void get_vmalloc_info(struct vmalloc_info *vmi)
> +{
> +	u64 gen = READ_ONCE(vmap_info_gen);
> +
> +	/*
> +	 * If the generation counter of the cache matches that of
> +	 * the vmalloc generation counter then return the cache:
> +	 */
> +	if (READ_ONCE(vmap_info_cache_gen) == gen) {

Why are those things u64? It has the obvious down-side that you still
get split loads on 32bit machines.

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