[Haifux] SSD and linux

[Doron Zuckerman]

Hi Gabi and Muli,
I'm sorry about the mistake- you understood me correctly.

I'm not sure it will speed up the OS, however I'm doing an academic research
on the matter as part of a project I'm taking, and I plan to check this
point.
The leading thought was that since the SSD is not a mechanical drive, pages
can be brought faster in this way, and there is no need to context switch,
thus, avoiding the overhead included.

Yes I plan to use the polling system (busy-wait) , and I'm looking for the
kernel part  in the pagefault handling mechanism in which the process is
suspended in order to prevent it.

So far I found the function "__generic_make_request" in file "ll_blk".
This function calls a sub function named "might_sleep".
I have deleted the call to this function whenever I'm in a pagefault,
however I'm not sure if this function casuses the sleep, or is just used for
debugging in order to check if we entered a suspend state.

My question is if this is the function I should change in order to accept
the change I'm willing to get, or if the change should be made in
q->make_request_fn
which, according to my understanding, belongs to the specific driver I'm
using.

Please help me find the specific place I'm looking for that would make the
desired change.

Thank you very much,
Doron.

On Tue, Sep 16, 2008 at 2:42 PM, gabik
<gabik at cs.technion.ac.il<https://mail.google.com/mail?view=cm&tf=0&to=gabik@cs.technion.ac.il>
> wrote:

>  Hello Doron
>
> Why do you think it will speed up the OS?
> What do you plan to do until the page is swapped in? Busy loop?
>
> About your solution:
> handle_mm_fault is called from within page fault handler (do_page_fault<http://lxr.linux.no/linux+v2.6.26.5/+code=do_page_fault>
> ()).
> So what is the rational behind calling handle_mm_fault not from inside
> pagefault  handler?
> Where would you call it from instead and what do you plan to do when you
> are in the page fault?
>
> Probably what you meant is, in order not to do context switch due to page
> fault, is to call handle_mm_fault as usual, but not to raise need_resched
> flag, so as not to trigger a context switch in case of a major page fault.
>
>
> Gabi
>
>
>
>  ------------------------------
> *From:* haifux-bounces at haifux.org<https://mail.google.com/mail?view=cm&tf=0&to=haifux-bounces@haifux.org>[mailto:
> haifux-bounces at haifux.org<https://mail.google.com/mail?view=cm&tf=0&to=haifux-bounces@haifux.org>]
> *On Behalf Of *Doron Zuckerman
> *Sent:* Tuesday, September 16, 2008 12:31 PM
> *To:* haifux at haifux.org<https://mail.google.com/mail?view=cm&tf=0&to=haifux@haifux.org>
> *Cc:* Ronen Gruengras
> *Subject:* [Haifux] SSD and linux
>
>  Hi all,
>
> I have a question regarding the linux kernel (for those of you who are
> familiar with it).
>
> I'm looking for a way to add a change to the linux kernel in order to check
> if I can make it more compatible with my Asus EEE-PC.
> I would like to change the kernel in such way that it will not do a context
> switch every time there is a page fault
> and will wait for the required page to be brought from the SSD (Solid State
> Drive), then continue as usual.
> In Such way, I plan to check if I can fasten the speed of the Operating
> System (Ubuntu for EEE).
> I thought of adding a TIF flag in the process descriptor (thread_info_32.h)
> that will tell me if I'm currently in a pagefault and
> then change the fault_32.c in such way that it will do the
> "handle_mm_fault(mm,vma, address, write_;" only if there is no
> pagefault at the moment.
> Can you suggest any other solution possible or tell me what you think about
> this solution.
>
> I would really appreciate any help with this,
> Doron.
>
>
>
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