cvs commit: src/sys/kern vfs_bio.c vfs_subr.c src/sys/sys buf.h proc.h src/sys/ufs/ffs ffs_snapshot.c

Don Lewis truckman at
Thu Sep 29 18:30:02 PDT 2005

truckman    2005-09-30 01:30:01 UTC

  FreeBSD src repository

  Modified files:
    sys/kern             vfs_bio.c vfs_subr.c 
    sys/sys              buf.h proc.h 
    sys/ufs/ffs          ffs_snapshot.c 
  Un-staticize runningbufwakeup() and staticize updateproc.
  Add a new private thread flag to indicate that the thread should
  not sleep if runningbufspace is too large.
  Set this flag on the bufdaemon and syncer threads so that they skip
  the waitrunningbufspace() call in bufwrite() rather than than
  checking the proc pointer vs. the known proc pointers for these two
  threads.  A way of preventing these threads from being starved for
  I/O but still placing limits on their outstanding I/O would be
  Set this flag in ffs_copyonwrite() to prevent bufwrite() calls from
  blocking on the runningbufspace check while holding snaplk.  This
  prevents snaplk from being held for an arbitrarily long period of
  time if runningbufspace is high and greatly reduces the contention
  for snaplk.  The disadvantage is that ffs_copyonwrite() can start
  a large amount of I/O if there are a large number of snapshots,
  which could cause a deadlock in other parts of the code.
  Call runningbufwakeup() in ffs_copyonwrite() to decrement runningbufspace
  before attempting to grab snaplk so that I/O requests waiting on
  snaplk are not counted in runningbufspace as being in-progress.
  Increment runningbufspace again before actually launching the
  original I/O request.
  Prior to the above two changes, the system could deadlock if enough
  I/O requests were blocked by snaplk to prevent runningbufspace from
  falling below lorunningspace and one of the bawrite() calls in
  ffs_copyonwrite() blocked in waitrunningbufspace() while holding
  See <>
  Revision  Changes    Path
  1.495     +3 -3      src/sys/kern/vfs_bio.c
  1.648     +2 -1      src/sys/kern/vfs_subr.c
  1.190     +1 -0      src/sys/sys/buf.h
  1.436     +1 -1      src/sys/sys/proc.h
  1.104     +16 -4     src/sys/ufs/ffs/ffs_snapshot.c

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