Messages in this thread | | | From | "jdow" <> | Subject | Re: Heuristic readahead for filesystems | Date | Wed, 11 Sep 2002 10:03:02 -0700 |
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From: "Davide Libenzi" <davidel@xmailserver.org> > On Wed, 11 Sep 2002, Xuan Baldauf wrote: > > > Hello, > > > > I wonder wether Linux implements a kind of heuristic > > readahead for filesystems: > > > > If an application reads a directory with getdents() and if > > in the past, it stat()ed a significant part of the directory > > entries, it is likely that it will stat() every entry of > > every directory it reads with getdents() in the future. Thus > > readahead for the stat data could improve the perfomance, > > especially if the stat data is located closely to each other > > on disk. > > > > If an application did a stat()..open()..read() sequence on a > > file, it is likely that, after the next stat(), it will open > > and read the mentioned file. Thus, one could readahead the > > start of a file on stat() of that file. > > > > Combined: If an application walks a directory tree and > > visits each file, it is likely that it will continue up to > > the end of that tree. > > M$ Win XP does exactly something like this and keep applications > ( windows\prefetch ) and boot profiles that it uses to prefetch disk data > and avoid long page fault latencies. It does kind-of-work but care should > be taken adopting a similar technique on Linux ( patents ).
Davide, when was the patent on readahead taken out? It has either expired or I can prove prior art I did myself on the old StarDrive and HardFrame controllers for the Amiga made by Microbotics, Inc.
{^_^} Joanne Dow, jdow@earthlink.net
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