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

[Andrew Morton]

On Thu, 31 Jan 2013 22:49:50 +0100
Jan Kara <jack@xxxxxxx> 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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