cvs commit: src/sys/kern uipc_syscalls.c src/sys/sys socketvar.h

Jeffrey Hsu hsu at
Wed Dec 10 14:27:16 PST 2003

hsu         2003/12/10 14:26:19 PST

DragonFly src repository

  Modified files:
    sys/kern             uipc_syscalls.c 
    sys/sys              socketvar.h 
  This patch improves the performance of sendfile(2).  It adds a hash
  table of active sf_buf mappings to ensure there is exactly one
  (ref-counted) sf_buf for each vm_page.  This saves on the number
  of sf_bufs used when sendfile(2) sends the same file over and over
  again to multiple connections simultaneously.  It also does lazy
  updates on the hw page table when a sf_buf ref count goes to zero,
  placing them on a freelist instead, in effect, making sf_bufs a
  cache of virtual-to-physical translations with LRU replacement on
  the inactive sf_bufs.  Finally, it does a wakeup_one() instead of
  a broadcast wakeup() when a free sf_buf becomes available.
  This patch roughly corresponds to FreeBSD revs 1.219 and 1.220 of
    revision 1.219
    date: 2003/11/17 18:22:24;  author: alc;  state: Exp;  lines: +48 -26
    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
    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.
    revision 1.220
    date: 2003/12/07 22:49:25;  author: alc;  state: Exp;  lines: +10 -9
    Don't remove the virtual-to-physical mapping when an sf_buf is freed.
    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 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.
  Reviewed by:	dillon
  Revision  Changes    Path
  1.21      +58 -31    src/sys/kern/uipc_syscalls.c
  1.7       +4 -3      src/sys/sys/socketvar.h

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