Messages in this thread |  | | Date | Wed, 11 Sep 2002 09:33:52 -0700 (PDT) | From | Davide Libenzi <> | Subject | Re: Heuristic readahead for filesystems |
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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
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