AWARE SYSTEMS
TIFF and LibTiff Mail List Archive

Thread

2008.10.14 18:00 "[Tiff] debugging on Windows", by Rajmohan Banavi
2008.10.14 23:15 "Re: [Tiff] debugging on Windows", by Bob Friesenhahn
2008.10.15 04:36 "Re: [Tiff] debugging on Windows", by Rajmohan Banavi
2008.11.14 08:29 "[Tiff] Memory leak (TIFFOpen, TIFFReadTile)?", by Ilkka Korpela
2008.11.14 17:49 "Re: [Tiff] Memory leak (TIFFOpen, TIFFReadTile)?", by Bob Friesenhahn
2008.11.14 18:37 "Re: [Tiff] Memory leak (TIFFOpen, TIFFReadTile)?", by Ilkka Korpela
2008.11.14 19:11 "Re: [Tiff] Memory leak (TIFFOpen, TIFFReadTile)?", by Frank Warmerdam
2008.11.14 21:37 "Re: [Tiff] Memory leak (TIFFOpen, TIFFReadTile)?", by Craig Bruce
2008.11.14 22:13 "Re: [Tiff] Memory leak (TIFFOpen, TIFFReadTile)?", by Phillip Crews
2008.11.14 23:31 "Re: [Tiff] Memory leak (TIFFOpen, TIFFReadTile)?", by Bob Friesenhahn
2008.11.15 17:07 "Re: [Tiff] Memory leak (TIFFOpen, TIFFReadTile)?", by Craig Bruce
2008.11.17 16:33 "Re: [Tiff] Memory leak (TIFFOpen, TIFFReadTile)?", by Bob Friesenhahn
2008.11.17 17:20 "Re: [Tiff] Memory leak (TIFFOpen, TIFFReadTile)?", by Frank Warmerdam
2008.11.17 17:39 "Re: [Tiff] Memory leak (TIFFOpen, TIFFReadTile)?", by Bob Friesenhahn
2008.11.19 20:09 "Re: [Tiff] Memory leak (TIFFOpen, TIFFReadTile)?", by Frank Warmerdam
2008.11.19 20:21 "Re: [Tiff] Memory leak (TIFFOpen, TIFFReadTile)?", by Craig Bruce
2008.11.19 20:47 "Re: [Tiff] Memory leak (TIFFOpen, TIFFReadTile)?", by Edward Lam
2008.11.19 20:56 "Re: [Tiff] Memory leak (TIFFOpen, TIFFReadTile)?", by Andy Cave
2008.11.20 04:17 "Re: [Tiff] Memory leak (TIFFOpen, TIFFReadTile)?", by Ron
2008.11.20 04:47 "Re: [Tiff] Memory leak (TIFFOpen, TIFFReadTile)?", by Bob Friesenhahn
2008.11.20 08:17 "Re: [Tiff] Memory leak (TIFFOpen, TIFFReadTile)?", by John
2008.11.19 21:09 "Re: [Tiff] Memory leak (TIFFOpen, TIFFReadTile)?", by Craig Bruce
2008.11.17 21:44 "Re: [Tiff] Memory leak (TIFFOpen, TIFFReadTile)?", by John
2008.11.17 22:22 "Re: [Tiff] Memory leak (TIFFOpen, TIFFReadTile)?", by Bob Friesenhahn
2008.11.17 22:47 "Re: [Tiff] Memory leak (TIFFOpen, TIFFReadTile)?", by John
2008.11.14 22:03 "Re: [Tiff] Memory leak (TIFFOpen, TIFFReadTile)?", by Phillip Crews

2008.11.17 16:33 "Re: [Tiff] Memory leak (TIFFOpen, TIFFReadTile)?", by Bob Friesenhahn

Every modern kernel will cache file content in memory no matter what access mode is used. However, ordinary access modes don't have the pathological thrashing problem that memory-mapped access does.

Right, every OS does cache data. The degree of caching varies considerably across OSs. The main benefit of using the memory mapping is that it allows repeated data access with "zero copy". As long as the "pathological thrashing" problem (also *very* OS dependent) is not evident, repeated reads are much faster when using memory mapping. Most (>80%) of computing data access is reads.

My application defaults to using programmed I/O. The reason for this is that I found that read-ahead algorithms often work much better with programmed I/O if the file is accessed over a network. Few operating systems are willing to speculatively read more than 8, 16, or 32K ahead when the file is accessed over a network. With programmed I/O a a larger read size can be requested so the OS feels safe about its use of the network. Some operating systems do not perform read ahead at all when memory mapping is used, and so each page fault (a page might be as small as 4K) results in the addition of network access latency and therefore substantially reduced read performance.

Bob
======================================
Bob Friesenhahn
bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/