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SubjectRe: PATCH: killing read_ahead[]
Jeff Garzik wrote:
>
> > Please have a look at the following patch and feel free to be scared
> > by the fact how UTTERLY BROKEN and ARBITRARY the current usage of the
> > read_ahead[] array and during the whole past decade was!
> > If you really care about clean internal interfaces this should be
> > one of those prio number ONE targets to shoot at...
> >
> > The most amanzing thing is that the whole test10-pre5 kernel with this
> > patch applied doesn't show any performance penalties for me at all!
> > And of corse it's about 10k smaller...
>
> I agree with you and Rik that this array needs to go away... but
> ripping out the feature is not the answer, IMHO.
>
> Can you work up a patch that instead changes the readahead to be a hash
> table? The key could be a hash of the blkdev/chrdev pointer value (or
> kdev_t for now). Considering the number of users, the hash table can be
> pretty darn small for most machines, but we can easily scale its size
> dynamically at boot if need be.
>
> That would give us the per-device granularity we need to actually make
> the feature useful, and allow us to kill the hacks you mention in
> existing drivers (like the MD and SCSI examples you cited).

A log log time ago (about 2.3.xx) I actually posted a patch
which was the preparation for *EXACTLY* this step and
which contained a bit of *OBVIOUS* other cleanup. However those times
I requested to get a confirmation that if I start to work *SERIOUSLY* on
it
then it wouldn't be for nothing. I don't intend to spend my
spare time on such a thing without knowing IN FRONT
that this work won't get ignored due to the IGNORANCE of some person.
I didn't get any clean response...

Anyway if you ask whatever I'm able to prepare such a patch the answer
is - obviously yes.

PS. This is an general problem of the "Open Source" developement modell
-
exagerous waiste of resources where many profesionalls don't wan't to
be involved with - however if you would dare to invite me to France for
a hack session of about 2-3 days I would deligtefully take hollidays
from my current job or a prolonged weekend
and do it anyway whatever "big L" says (or doesnt say ;-).
-
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