Date: Wed, 10 Nov 2004 22:00:35 -0500 From: David Schultz <das@FreeBSD.ORG> To: arch@FreeBSD.ORG Subject: U Area Removal Message-ID: <20041111030035.GA70923@VARK.MIT.EDU>
next in thread | raw e-mail | index | archive | help
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.
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20041111030035.GA70923>