On Mon, Feb 15, 2021 at 03:44:52PM +0000, David Howells wrote: > Provide a function, readahead_expand(), that expands the set of pages > specified by a readahead_control object to encompass a revised area with a > proposed size and length. > > The proposed area must include all of the old area and may be expanded yet > more by this function so that the edges align on (transparent huge) page > boundaries as allocated. > > The expansion will be cut short if a page already exists in either of the > areas being expanded into. Note that any expansion made in such a case is > not rolled back. > > This will be used by fscache so that reads can be expanded to cache granule > boundaries, thereby allowing whole granules to be stored in the cache, but > there are other potential users also. So looking at linux-next this seems to have a user, but that user is dead wood given that nothing implements ->expand_readahead. Looking at the code structure I think netfs_readahead and netfs_rreq_expand is a complete mess and needs to be turned upside down, that is instead of calling back from netfs_readahead to the calling file system, split it into a few helpers called by the caller. But even after this can't we just expose the cache granule boundary to the VM so that the read-ahead request gets setup correctly from the very beginning?
