Re: Drastic Slowdown of 'fseek()' Calls From 2.4 to 2.6 -- VMM Change?

[Nick Piggin]

Hans Reiser wrote:

> Sounds like the real problem is that glibc is doing filesystem
> optimizations without making them conditional on the filesystem type. 

I'm not sure that it should even be conditional on the filesystem type...
To me it seems silly to even bother doing it, although I guess there
is another level of buffering involved which might mean it makes more
sense.

> Does anyone know the email address of the glibc guy so we can ask him
> not to do that?

Ulrich Drepper I guess. But don't tell him I sent you ;)

> My entry for the ugliest thought of the day: I wonder if the kernel can
> test the glibc version and.....
>
> Hans
>
> Nick Piggin wrote:
>
>
> > Actually glibc tries to turn this pre-read off if the seek is to a page
> > aligned offset, presumably to handle this case. However a big write
> > would only have to RMW the first and last partial pages, so pre-reading
> > 128KB in this case is wrong.
> >
> > And I would also say a 4K read is wrong as well, because a big read will
> > be less efficient due to the extra syscall and small IO.
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