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From: Scott Long <scottl@FreeBSD.org>
Date: Sun, 29 Jan 2006 08:24:54 +0000 (UTC)
To: src-committers@FreeBSD.org, cvs-src@FreeBSD.org, cvs-all@FreeBSD.org
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Cc: 
Subject: cvs commit: src/sys/vm vm_contig.c
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scottl      2006-01-29 08:24:54 UTC

  FreeBSD src repository

  Modified files:
    sys/vm               vm_contig.c 
  Log:
  The change a few years ago of having contigmalloc start its scan at the top
  of physical RAM instead of the bottom was a sound idea, but the implementation
  left a lot to be desired.  Scans would spend considerable time looking at
  pages that are above of the address range given by the caller, and multiple
  calls (like what happens in busdma) would spend more time on top of that
  rescanning the same pages over and over.
  
  Solve this, at least for now, with two simple optimizations.  The first is
  to not bother scanning high ordered pages that are outside of the provided
  address range.  Second is to cache the page index from the last successful
  operation so that subsequent scans don't have to restart from the top.  This
  is conditional on the numpages argument being the same or greater between
  calls.
  
  MFC After: 2 weeks
  
  Revision  Changes    Path
  1.48      +19 -2     src/sys/vm/vm_contig.c