Date: Thu, 11 Nov 2004 17:18:10 -0700 From: Scott Long <scottl@freebsd.org> To: David Schultz <das@freebsd.org> Cc: arch@freebsd.org Subject: Re: U Area Removal Message-ID: <41940142.2040401@freebsd.org> In-Reply-To: <20041111030035.GA70923@VARK.MIT.EDU> References: <20041111030035.GA70923@VARK.MIT.EDU>
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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. This breaks amd64 in bad ways on boot. I'll send a trace and more info when I get a serial console hooked up. Scott
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