Re: Test program with VM or FS problems

[Andrew Morton <akpm@osdl.org>]

jlnance@unity.ncsu.edu wrote:
>
>  Hello Andrew,
>      About a year ago I told you I would get you some more information
>  about a problem I was seeing that might be in the Linux VM or ext{2,3}
>  code.

I thought you'd forgotten!

>  For most of the run the temp file is smaller
>  than this.  So for most of the run both files will fit into the
>  memory of the machine.  Thus I would expect the program to run
>  quickly, because it will not need to touch the disk.  Things are
>  in cache.  This is not what I see.  Instead the program seems to
>  be very much disk bound.

I bet the use-once page replacement heuristic is doing the wrong thing.  I
noticed it playing up once - the machine had 30M on the inactive list and
reading a 40M file repeatedly caused that file to never get cached.  it
just kept on reclaiming itself.