Date: Tue, 25 Feb 2014 19:35:22 +0100
From: Peter Zijlstra <peterz@infradead.org>
To: Davidlohr Bueso <davidlohr@hp.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, Ingo Molnar <mingo@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Michel Lespinasse <walken@google.com>, Mel Gorman <mgorman@suse.de>,
        Rik van Riel <riel@redhat.com>,
        KOSAKI Motohiro <kosaki.motohiro@gmail.com>, aswin@hp.com,
        scott.norton@hp.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] mm: per-thread vma caching
Message-ID: <20140225183522.GU6835@laptop.programming.kicks-ass.net>
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On Tue, Feb 25, 2014 at 10:16:46AM -0800, Davidlohr Bueso wrote:
> +void vmacache_update(struct mm_struct *mm, unsigned long addr,
> +		     struct vm_area_struct *newvma)
> +{
> +	/*
> +	 * Hash based on the page number. Provides a good
> +	 * hit rate for workloads with good locality and
> +	 * those with random accesses as well.
> +	 */
> +	int idx = (addr >> PAGE_SHIFT) & 3;

 % VMACACHE_SIZE

perhaps? GCC should turn that into a mask for all sensible values I
would think.

Barring that I think something like:

#define VMACACHE_BITS	2
#define VMACACHE_SIZE	(1U << VMACACHE_BITS)
#define VMACACHE_MASK	(VMACACHE_SIZE - 1)

Might do I suppose.

> +	current->vmacache[idx] = newvma;
> +}
> -- 
> 1.8.1.4
> 
> 
> 
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