Re: Suggestion for O_DIRECT and friends

Jakub Jelinek (jj@sunsite.ms.mff.cuni.cz)
Sun, 20 Dec 1998 19:44:15 +0100 (CET)


> O_Serialized
> Hints the kernel that the file is read in a serial/linear way,
> and that caching old results isn't usefull but that Read-ahead,
> Read-behind and Write-clustering are.
>
> Possible usage:
> * Multimedia applications (video-streaming, MP3-playing)
Right.
* CD-ROM burning

> * tar, gzip and others
> * grep
> * Reading configuration-files

But these three are generally not good examples. You want to cache stuff
unless it is huge. E.g. doing grep over and over on a kernel tree is quite
frequent, if you have enough memory, then you finish with having entire
source tree in the cache after the first run.
So such hints should be given only if the applications either know the
transfered amounts are huge, or they can be sure nobody will use it again
soon. The generic apps you listed don't know anything about the data.

Cheers,
Jakub
___________________________________________________________________
Jakub Jelinek | jj@sunsite.mff.cuni.cz | http://sunsite.mff.cuni.cz
Administrator of SunSITE Czech Republic, MFF, Charles University
___________________________________________________________________
UltraLinux | http://ultra.linux.cz/ | http://ultra.penguin.cz/
Linux version 2.1.130 on a sparc64 machine (3958.37 BogoMips)
___________________________________________________________________

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