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From: Robert Watson <rwatson@FreeBSD.org>
Date: Mon, 2 Apr 2001 21:09:54 -0700 (PDT)
To: cvs-committers@FreeBSD.org, cvs-all@FreeBSD.org
Subject: cvs commit: src/sys/ufs/ufs ufs_extattr.c
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rwatson     2001/04/02 21:09:54 PDT

  Modified files:
    sys/ufs/ufs          ufs_extattr.c 
  Log:
  o Change the default from using IO_SYNC on EA set and delete operations
    to not using IO_SYNC.  Expose a sysctl (debug.ufs_extattr_sync) for
    enabling the use of IO_SYNC.
  
      - Use of IO_SYNC substantially degrades ACL performance when a
        default ACL is set on a directory, as there are four synchronous
        writes initiated to define both supporting EAs for new
        sub-directories, and to set the data; two for new files.  Later, this
        may be optimized to two writes for sub-directories, one for new
        files.
  
      - IO_SYNC does not substantially improve consistency properties due
        to the poor consistency properties of existing permissions (which
        ACLs are a superset of), due to interaction with soft updates,
        and due to differences in handling consistency for data and file
        system meta-data.
  
      - In macro-benchmarks, this reduces the overhead of setting default
        ACLs down to the same overhead as enabling ACLs on a file system
        and not using them.  Enabling ACLs still introduces a small
        overhead (I measure 7% on a -j 2 buildworld with pre-allocated
        EA backing store, but this is not rigorous testing, nor in any way
        optimized).
  
      - The sysctl will probably change to another administration method
        (or at least, a better name) in the near future, but consistency
        properties of EAs are still being worked out.  The toggle is defined
        right now to allow easier performance analysis and exploration
        of possible guarantees.
  
  Obtained from:	TrustedBSD Project
  
  Revision  Changes    Path
  1.29      +24 -10    src/sys/ufs/ufs/ufs_extattr.c


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