linux-kernel - Re: [PATCH 3/3] mm,vmacache: optimize overflow system-wide flushing

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Message-ID: <1397520133.31076.24.camel@buesod1.americas.hpqcorp.net>
Date:	Mon, 14 Apr 2014 17:02:13 -0700
From:	Davidlohr Bueso <davidlohr@...com>
To:	akpm@...ux-foundation.org
Cc:	linux-mm@...ck.org, linux-kernel@...r.kernel.org, aswin@...com,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH 3/3] mm,vmacache: optimize overflow system-wide flushing

Stupid script... Cc'ing Oleg.

On Mon, 2014-04-14 at 16:57 -0700, Davidlohr Bueso wrote:
> For single threaded workloads, we can avoid flushing
> and iterating through the entire list of tasks, making
> the whole function a lot faster, requiring only a single
> atomic read for the mm_users.
> 
> Suggested-by: Oleg Nesterov <oleg@...hat.com>
> Signed-off-by: Davidlohr Bueso <davidlohr@...com>
> ---
>  mm/vmacache.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/mm/vmacache.c b/mm/vmacache.c
> index e167da2..61c38ae 100644
> --- a/mm/vmacache.c
> +++ b/mm/vmacache.c
> @@ -17,6 +17,16 @@ void vmacache_flush_all(struct mm_struct *mm)
>  {
>  	struct task_struct *g, *p;
>  
> +	/*
> +	 * Single threaded tasks need not iterate the entire
> +	 * list of process. We can avoid the flushing as well
> +	 * since the mm's seqnum was increased and don't have
> +	 * to worry about other threads' seqnum. Current's
> +	 * flush will occur upon the next lookup.
> +	 */
> +	if (atomic_read(&mm->mm_users) == 1)
> +		return;
> +
>  	rcu_read_lock();
>  	for_each_process_thread(g, p) {
>  		/*


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