Subject: Re: [PATCH 2/2] mm: make do_writepages() use plugging
From: Peter Zijlstra <a.p.zijlstra@chello.nl>
To: Amit Sahrawat <amit.sahrawat83@gmail.com>
Cc: Wu Fengguang <fengguang.wu@intel.com>, Jan Kara <jack@suse.cz>,
        Andrew Morton <akpm@linux-foundation.org>,
        Johannes Weiner <jweiner@redhat.com>,
        Amit Sahrawat <a.sahrawat@samsung.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
In-Reply-To: <1328275626-5322-1-git-send-email-amit.sahrawat83@gmail.com>
References: <1328275626-5322-1-git-send-email-amit.sahrawat83@gmail.com>
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Date: Fri, 03 Feb 2012 14:32:28 +0100
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On Fri, 2012-02-03 at 18:57 +0530, Amit Sahrawat wrote:
> This will cover all the invocations for writepages to be called with
> plugging support.

This changelog fails to explain why this is a good thing... I thought
the idea of the new plugging stuff was that we now don't need to
sprinkle plugs all over the kernel..

> Signed-off-by: Amit Sahrawat <a.sahrawat@samsung.com>
> ---
>  mm/page-writeback.c |    4 ++++
>  1 files changed, 4 insertions(+), 0 deletions(-)
> 
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 363ba70..2bea32c 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -1866,14 +1866,18 @@ EXPORT_SYMBOL(generic_writepages);
>  
>  int do_writepages(struct address_space *mapping, struct writeback_control *wbc)
>  {
> +	struct blk_plug plug;
>  	int ret;
>  
>  	if (wbc->nr_to_write <= 0)
>  		return 0;
> +
> +	blk_start_plug(&plug);
>  	if (mapping->a_ops->writepages)
>  		ret = mapping->a_ops->writepages(mapping, wbc);
>  	else
>  		ret = generic_writepages(mapping, wbc);
> +	blk_finish_plug(&plug);
>  	return ret;
>  }
>  


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