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Date:      Thu, 13 Dec 2001 16:15:06 -0800 (PST)
From:      Kirk McKusick <mckusick@FreeBSD.org>
To:        cvs-committers@FreeBSD.org, cvs-all@FreeBSD.org
Subject:   cvs commit: src/sys/ufs/ffs ffs_alloc.c ffs_snapshot.c ffs_vfsops.c fs.h
Message-ID:  <200112140015.fBE0F6Q99440@freefall.freebsd.org>

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mckusick    2001/12/13 16:15:06 PST

  Modified files:
    sys/ufs/ffs          ffs_alloc.c ffs_snapshot.c ffs_vfsops.c 
                         fs.h 
  Log:
  Minimize the time necessary to suspend operations on a filesystem
  when taking a snapshot. The two time consuming operations are
  scanning all the filesystem bitmaps to determine which blocks
  are in use and scanning all the other snapshots so as to be able
  to expunge their blocks from the view of the current snapshot.
  The bitmap scanning is broken into two passes. Before suspending
  the filesystem all bitmaps are scanned. After the suspension,
  those bitmaps that changed after being scanned the first time
  are rescanned. Typically there are few bitmaps that need to be
  rescanned. The expunging of other snapshots is now done after
  the suspension is released by observing that we can easily
  identify any blocks that were allocated to them after the
  suspension (they will be maked as `not needing to be copied'
  in the just created snapshot). For all the gory details, see
  the ``Running fsck in the Background'' paper in the Usenix
  BSDCon 2002 Conference Proceedings, pages 55-64.
  
  Revision  Changes    Path
  1.82      +15 -1     src/sys/ufs/ffs/ffs_alloc.c
  1.24      +193 -96   src/sys/ufs/ffs/ffs_snapshot.c
  1.164     +1 -0      src/sys/ufs/ffs/ffs_vfsops.c
  1.24      +3 -2      src/sys/ufs/ffs/fs.h

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