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more than one sf_buf for one vm_page. To accomplish this, we add a global hash table mapping vm_pages to sf_bufs and a reference count to each sf_buf. (This is similar to the patches for RELENG_4 at http://www.cs.princeton.edu/~yruan/debox/.) For the uninitiated, an sf_buf is nothing more than a kernel virtual address that is used for temporary virtual-to-physical mappings by sendfile(2) and zero-copy sockets. As such, there is no reason for one vm_page to have several sf_bufs mapping it. In fact, using more than one sf_buf for a single vm_page increases the likelihood that sendfile(2) blocks, hurting throughput. (See http://www.cs.princeton.edu/~yruan/debox/.)