Re: U Area Removal
From: Brian Fundakowski Feldman (green_at_FreeBSD.ORG)
Date: 11/11/04
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Date: Wed, 10 Nov 2004 22:16:39 -0500 To: arch@FreeBSD.ORG
On Wed, Nov 10, 2004 at 10:00:35PM -0500, David Schultz wrote:
> Over the years, the amount of data we have stored in each process' U
> area has eroded to the point where all we have left are the following:
>
> - A struct kinfo_proc that is only used for a.out core dumps.
> This can be reconstructed at the time of the core dump, so
> it doesn't need to be there.
>
> - The struct pstats for the process, which takes a mere 216 bytes
> on i386.
>
> In exchange for the ability to swap out this 216-byte structure, we
> keep around a 4096-byte page, a 132-byte vm_object, and a couple of
> pointers. Moreover, there is a small amount of runtime overhead
> associated with this, and developers need to remember to PHOLD() and
> PRELE() the process as appropriate.[1]
>
> I propose to remove the ability to swap the U area, allocating p_stats
> from malloced memory instead. Medium-term scheduling and swapping of
> kernel stacks would be retained. Here are the patches; !i386 testers
> wanted:
>
> http://www.freebsd.org/~das/patches/upages.diff
>
>
> [1] Most of the instances of PHOLD() and PRELE() right now never
> needed to be there or have been unnecessary ever since the PCB
> was moved out of the U area.
I am not going to get a chance to review this soon (which I'd like to)
but I'm going to make sure I also voice support for removing this
extra avenue for system instability due to media failure. I am happy
to see you having the desire to take this step!
-- Brian Fundakowski Feldman \'[ FreeBSD ]''''''''''\ <> green@FreeBSD.org \ The Power to Serve! \ Opinions expressed are my own. \,,,,,,,,,,,,,,,,,,,,,,\ _______________________________________________ freebsd-arch@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-arch To unsubscribe, send any mail to "freebsd-arch-unsubscribe@freebsd.org"
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