[Ocfs2-devel] [PATCH 3/4] ocfs2: Add readhead during CoW.

[Joel Becker]

On Tue, Jun 29, 2010 at 04:35:40PM +0800, Tao Ma wrote:
> @@ -2953,6 +2957,14 @@ static int ocfs2_duplicate_clusters_by_page(handle_t *handle,
>  		if (PAGE_CACHE_SIZE <= OCFS2_SB(sb)->s_clustersize)
>  			BUG_ON(PageDirty(page));
>  
> +		if (PageReadahead(page) && context->file) {
> +			page_cache_async_readahead(mapping,
> +						   &context->file->f_ra,
> +						   context->file,
> +						   page, page_index,
> +						   readahead_pages);
> +		}

	This is merely re-sending the same pages that were already sent,
right?  In the previous patch, you asked the readahead code to try all
pages in the hunk.  Now you've discovered a page that isn't yet up to
date, and you send it (and the 1M next to it) back to readahead.
	This is, I assume, because the readahead code doesn't actually
read your entire request from page_cache_sync_readahead().  It just
reads some, and this is you hinting that you need the next bit.  Am I
right?

Joel

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Joel Becker
Consulting Software Developer
Oracle
E-mail: joel.becker at oracle.com
Phone: (650) 506-8127