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SubjectRe: PATCH: rewritten bdflush
Hi!

> >> There is one notable side effect: you don't have to run the user space
> >> update anymore, bdflush wakes up every so often all by itself. I
> >
> >How about notebook users who have configured update to stop writing out
> >buffers and spin down disks after some idle time?
> >
> >Does you patch implement something similar or do we need to spin up drives
> >every 5 seconds? ;)
>
> No, the patch doesn't do anything like that. However, it seems to
> me

Shame, so you've just broken notebooks.

> that if your system really is idle, there won't be any dirty buffers
> to flush, and the disk will spin down anyway. It also seems to me

Ok, but it gives sense not to spin up even if there are few dirty
buffers. (Remember that nearly anything touches atimes of files which
means dirty buffers!)

> that it is unsafe behavior to postpone flushing dirty buffers just
> because the disk has spun down. Finally, does anyone necessarily
> know

It may be unsafe, but I'll rather be unsafe and sleep at night.

> when the disk is spun down? You'd need something in the disk
>driver,

We exactly know when disks are spun down -- becuase it is bdflush
which spins them down. So it knows it spun them down and it can
detect spin up by increased numbers in /proc/stat.


> and there doesn't seem to be anything like that. The versions of
> update that `know' this seem to do it by looking at /proc/interrupts,
> which is unreliable.

My version of bdflush parses /proc/stat, field disk_rio. It is not
completely safe but it works well enough.

Pavel
PS: Did that patch go into 2.2.8? I'm afraid it did :-(.

--
The best software in life is free (not shareware)! Pavel
GCM d? s-: !g p?:+ au- a--@ w+ v- C++@ UL+++ L++ N++ E++ W--- M- Y- R+

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