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SubjectRe: large files unnecessary trashing filesystem cache?
Zitat von Bodo Eggert <7eggert@gmx.de>:
> You can alyo cat a big file into /dev/null. I made those examples in order
> to demonstrate the problem with using O_DIRECT.

O_DIRECT has to much impact at the mentioned "vdr" due to unwanted side effects
either.

>
> OTOH, I don't realtime stuff on my computer, so I'm not really affected,
> but I'll try to show it anyway.
>
> > > Changing a few programs will only partly cover the problems.
> > >
> > > I guess the solution would be using random cache eviction rather than
> > > a FIFO. I never took a look the cache mechanism, so I may very well be
> > > wrong here.
> >
> > Read-only pages should be re-cycled really easily & quickly. I can't
> > belive read-only pages are causing you all the trouble.
>
> Just a q&d test:
>
> $ time ls -l $DIR > /dev/null
> real 0m0.442s
> user 0m0.008s
> sys 0m0.024s
>
> $ time ls -l $DIR > /dev/null
> real 0m0.077s
> user 0m0.008s
> sys 0m0.008s
>
> cat $BIGFILES_1.5GB > /Dev/null
>
> $ time ls -l $DIR > /dev/null
> real 0m0.270s
> user 0m0.008s
> sys 0m0.008s
>
> $ time ls -l $DIR > /dev/null
> real 0m0.078s
> user 0m0.004s
> sys 0m0.004s
>
>
Thanks for pointing this out - this clearly shows the effect.
Now consider a mildly loaded multitasking environment running X, some services,
window-manager, email, maybe some databases and a streaming video-application
at once (so does mine) - the video-file will have unwanted impact on all the
other applications - leading to unnecessary reloads of lots of files, inodes
etc.
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