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f648022faa
Instead of using a linear index to address the pages, use the cookie of the first entry, since that is what we use to match the page anyway. This allows us to avoid re-reading the entire cache on a seekdir() type of operation. The latter is very common when re-exporting NFS, and is a major performance drain. The change does affect our duplicate cookie detection, since we can no longer rely on the page index as a linear offset for detecting whether we looped backwards. However since we no longer do a linear search through all the pages on each call to nfs_readdir(), this is less of a concern than it was previously. The other downside is that invalidate_mapping_pages() no longer can use the page index to avoid clearing pages that have been read. A subsequent patch will restore the functionality this provides to the 'ls -l' heuristic. Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>