linux-kernel - Re: [PATCH 2/6] fs: Take mapping lock in generic read paths

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Message-Id: <20130131155940.7b1f8e0e.akpm@linux-foundation.org>
Date:	Thu, 31 Jan 2013 15:59:40 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Jan Kara <jack@...e.cz>
Cc:	LKML <linux-kernel@...r.kernel.org>, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH 2/6] fs: Take mapping lock in generic read paths

On Thu, 31 Jan 2013 22:49:50 +0100
Jan Kara <jack@...e.cz> wrote:

> Add mapping lock to struct address_space and grab it in all paths
> creating pages in page cache to read data into them. That means buffered
> read, readahead, and page fault code.

Boy, this does look expensive in both speed and space.

As you pointed out in [0/n], it's 2-3%.  As always with pagecache
stuff, the cost of filling the page generally swamps any inefficiencies
in preparing that page.

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