freebsd-skq/sys/i386/include/sf_buf.h
Alan Cox 0543fa5398 - Change the i386's sf_buf implementation so that it never allocates
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/.)
2003-11-17 18:22:24 +00:00

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1.8 KiB
C

/*-
* Copyright (c) 2003 Alan L. Cox <alc@cs.rice.edu>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
*
* $FreeBSD$
*/
#ifndef _MACHINE_SF_BUF_H_
#define _MACHINE_SF_BUF_H_
#include <sys/queue.h>
struct vm_page;
struct sf_buf {
LIST_ENTRY(sf_buf) list_entry; /* list of buffers */
struct vm_page *m; /* currently mapped page */
vm_offset_t kva; /* va of mapping */
int ref_count; /* usage of this mapping */
};
static __inline vm_offset_t
sf_buf_kva(struct sf_buf *sf)
{
return (sf->kva);
}
static __inline struct vm_page *
sf_buf_page(struct sf_buf *sf)
{
return (sf->m);
}
#endif /* !_MACHINE_SF_BUF_H_ */