a5819cb5b5
Instead, allow the mapping to persist, but add the sf_buf to a free list. If a later sendfile(2) or zero-copy send resends the same physical page, perhaps with the same or different contents, then the mapping overhead is avoided and the sf_buf is simply removed from the free list. In other words, the i386 sf_buf implementation now behaves as a cache of virtual-to-physical translations using an LRU replacement policy on inactive sf_bufs. This is similar in concept to a part of http://www.cs.princeton.edu/~yruan/debox/ patch, but much simpler in implementation. Note: none of this is required on alpha, amd64, or ia64. They now use their direct virtual-to-physical mapping to avoid any emphemeral mapping overheads in their sf_buf implementations.
59 lines
1.9 KiB
C
59 lines
1.9 KiB
C
/*-
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* Copyright (c) 2003 Alan L. Cox <alc@cs.rice.edu>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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* ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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* ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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* OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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* HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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* OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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* SUCH DAMAGE.
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*
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* $FreeBSD$
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*/
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#ifndef _MACHINE_SF_BUF_H_
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#define _MACHINE_SF_BUF_H_
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#include <sys/queue.h>
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struct vm_page;
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struct sf_buf {
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LIST_ENTRY(sf_buf) list_entry; /* list of buffers */
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TAILQ_ENTRY(sf_buf) free_entry; /* list of buffers */
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struct vm_page *m; /* currently mapped page */
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vm_offset_t kva; /* va of mapping */
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int ref_count; /* usage of this mapping */
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};
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static __inline vm_offset_t
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sf_buf_kva(struct sf_buf *sf)
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{
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return (sf->kva);
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}
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static __inline struct vm_page *
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sf_buf_page(struct sf_buf *sf)
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{
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return (sf->m);
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}
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#endif /* !_MACHINE_SF_BUF_H_ */
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