cifs: don't cap ra_pages at the same level as default_backing_dev_info
While testing, I've found that even when we are able to negotiate a much larger rsize with the server, on-the-wire reads often end up being capped at 128k because of ra_pages being capped at that level. Lifting this restriction gave almost a twofold increase in sequential read performance on my craptactular KVM test rig with a 1M rsize. I think this is safe since the actual ra_pages that the VM requests is run through max_sane_readahead() prior to submitting the I/O. Under memory pressure we should end up with large readahead requests being suppressed anyway. Signed-off-by: Jeff Layton <jlayton@redhat.com> Signed-off-by: Steve French <sfrench@us.ibm.com>
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