linux-kernel - Re: [PATCH] writeback: avoid unnecessary determine_dirtyable

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Message-ID: <alpine.DEB.2.00.1101031400550.10636@chino.kir.corp.google.com>
Date:	Mon, 3 Jan 2011 14:03:31 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Minchan Kim <minchan.kim@...il.com>
cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-mm <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Wu Fengguang <fengguang.wu@...el.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] writeback: avoid unnecessary determine_dirtyable_memory
 call

On Tue, 4 Jan 2011, Minchan Kim wrote:

> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index fc93802..c340536 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -390,9 +390,12 @@ void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty)
>  {
>  	unsigned long background;
>  	unsigned long dirty;
> -	unsigned long available_memory = determine_dirtyable_memory();
> +	unsigned long available_memory;

You need unsigned long uninitialized_var(available_memory) to avoid the 
warning.

>  	struct task_struct *tsk;
>  
> +	if (!vm_dirty_bytes || !dirty_background_bytes)
> +		available_memory = determine_dirtyable_memory();
> +
>  	if (vm_dirty_bytes)
>  		dirty = DIV_ROUND_UP(vm_dirty_bytes, PAGE_SIZE);
>  	else
--
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