pdflush -> noflushd related question

pdflush -> noflushd related question

[Michael Buesch]

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Hi.

I want to fix the userspace noflushd daemon to run on 2.5 kernels,
but it seems to get *very* tricky, because bdflush, kupdated have been
replaced by pdflush.

I've grepped through the lkml-archives and I found a post from you, Andrew,
that sayed:

[SNIP]
Subject: [patch] replace kupdate and bdflush with pdflush

- - use a timer to kick off a pdflush thread every five seconds
  to run the kupdate code. 

- - wakeup_bdflush() kicks off a pdflush thread to run the current
  bdflush function.

There's some loss of functionality here - the ability to tune
the writeback periods.  The numbers are hardwired at present.
But the intent is that buffer-based writeback disappears
altogether.  New mechanisms for tuning the writeback will
need to be introduced.
[SNIP]


Yea, but it seems, that I need exactly this lost functionality. :)
noflushd, on 2.4 kernels, prevents the disks to spin up by spinning
them down an stopping the kupdated daemon through putting
the update-interval to 0 via syscall bdflush().
That's the code to do so:
bdflush(2 + (1 << 3) + 1, interval);

So, how to set the interval, or better sayed, how to _stop_
buffer flushing in 2.5?
Has this lost functionality already been re-implemented?
Are there new syscalls?

Thanks for your help.

- -- 
Regards Michael Büsch
http://www.8ung.at/tuxsoft
 18:29:24 up  4:01,  2 users,  load average: 1.11, 1.09, 1.05

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Re: pdflush -> noflushd related question

[Andrew Morton]

Michael Buesch <fsdeveloper@yahoo.de> wrote:
>
>  So, how to set the interval, or better sayed, how to _stop_
>  buffer flushing in 2.5?

/proc/sys/vm has the appropriate tunables.  They are documented in
Documentation/filesystems/proc.txt.

You can turn these guys off by setting the sysctls to 1000000000
I guess.   Problem is, I don't think there's a way of starting them
again until the ten million seconds expires.  hmm.

Re: pdflush -> noflushd related question

[Michael Buesch]

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On Saturday 31 May 2003 19:58, Andrew Morton wrote:
> Michael Buesch <fsdeveloper@yahoo.de> wrote:
> >  So, how to set the interval, or better sayed, how to _stop_
> >  buffer flushing in 2.5?
>
> /proc/sys/vm has the appropriate tunables.  They are documented in
> Documentation/filesystems/proc.txt.
>
> You can turn these guys off by setting the sysctls to 1000000000
> I guess.   Problem is, I don't think there's a way of starting them
> again until the ten million seconds expires.  hmm.

Thanks Andrew, that's a good point to goon hacking. :)
I'll look at it.

- -- 
Regards Michael Büsch
http://www.8ung.at/tuxsoft
 20:21:50 up  5:54,  2 users,  load average: 2.01, 2.02, 2.00

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Re: pdflush -> noflushd related question

[Michael Buesch]

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On Saturday 31 May 2003 19:58, Andrew Morton wrote:
> You can turn these guys off by setting the sysctls to 1000000000
> I guess.   Problem is, I don't think there's a way of starting them
> again until the ten million seconds expires.  hmm.

I've thought a little bit more about it.
Why do you think, there is no way of waking up?
Is it, because, when I set it to 1000000000 and the back to,
let's say, 500, the pdflush threads don't wake up to recognize
this change? Is this the cause?

What about signaling all pdflush threads with, for example,
for(ALL_PDFLUSHS)
	kill(pid, SIGSTOP);

Don't they wake up then and recognize the reducing of the timeout?
The old noflushd did so to wake up updated.

thanks.

- -- 
Regards Michael Büsch
http://www.8ung.at/tuxsoft
 20:32:32 up  6:04,  2 users,  load average: 2.05, 2.03, 2.00

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Re: pdflush -> noflushd related question

[Andrew Morton]

Michael Buesch <fsdeveloper@yahoo.de> wrote:
>
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
> 
> On Saturday 31 May 2003 19:58, Andrew Morton wrote:
> > You can turn these guys off by setting the sysctls to 1000000000
> > I guess.   Problem is, I don't think there's a way of starting them
> > again until the ten million seconds expires.  hmm.
> 
> I've thought a little bit more about it.
> Why do you think, there is no way of waking up?
> Is it, because, when I set it to 1000000000 and the back to,
> let's say, 500, the pdflush threads don't wake up to recognize
> this change? Is this the cause?

Yes.

> What about signaling all pdflush threads with, for example,
> for(ALL_PDFLUSHS)
> 	kill(pid, SIGSTOP);
> 
> Don't they wake up then and recognize the reducing of the timeout?
> The old noflushd did so to wake up updated.

No, that's OK - I'll fix it in the kernel.  It's pretty simple.