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SubjectRe: [RFC] Disk shock protection (revisited)
On Thu, Feb 28, 2008 at 6:13 AM, Alan Cox <alan@lxorguk.ukuu.org.uk> wrote:
> > > That sounds like a non starter. What if the box is busy, what if the
> > > daemon or something you touch needs memory and causes paging ?
> >
> > The daemon runs mlock'd anyway, so there won't be any need for paging
>
> mlock does not guarantee anything of that form. A syscall by an mlocked
> process which causes a memory allocation can cause paging of another
> process on the system.
>
>
> > there. As for responsiveness under heavy load, I'm not quite sure I get
> > your meaning. On my system, at least, the only way I have managed to
> > decrease responsiveness noticeably is to cause a lot of I/O operations
>
> It depends a lot on hardware but you can certainly get user space delays
> in seconds as an extreme worst case.

I don't know the details, but I believe the Linux-HA heartbeat daemons
take significant effort to eliminate unexpected delays. See
http://www.linux-ha.org/

Lars Marowsky-Bree of Novell is extremely involved in the project and
he at least occasionally posts on LKML. I've cc'ed him.

Greg
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