Date: Thu, 11 Nov 2004 12:28:18 -0500 From: John Baldwin <jhb@FreeBSD.org> To: freebsd-arch@FreeBSD.org Cc: David Schultz <das@FreeBSD.org> Subject: Re: U Area Removal Message-ID: <200411111228.19044.jhb@FreeBSD.org> In-Reply-To: <20041111030035.GA70923@VARK.MIT.EDU> References: <20041111030035.GA70923@VARK.MIT.EDU>
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On Wednesday 10 November 2004 10:00 pm, 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. Yay! Two notes: +struct pstats * +pstats_alloc(void) +{ + + return (malloc(sizeof(struct plimit), M_SUBPROC, M_ZERO|M_WAITOK)); +} I think you mean s/plimit/pstats/ there. Secondly: /* - * Per process structure containing data that isn't needed in core - * when the process isn't running (esp. when swapped out). + * Formerly the per-process structure containing data that isn't needed + * in core when the process is swapped out, this structure remains only + * for the benefit of a.out core dumps. */ s/out, this/out. This/ It's a whole new sentence. :) -- John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve" = http://www.FreeBSD.org
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