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Xref: sserve comp.unix.bsd:1807 comp.unix.wizards:26063 comp.unix.questions:24000 Path: sserve!manuel!munnari.oz.au!spool.mu.edu!agate!dog.ee.lbl.gov!horse.ee.lbl.gov!torek From: torek@horse.ee.lbl.gov (Chris Torek) Newsgroups: comp.unix.bsd,comp.unix.wizards,comp.unix.questions Subject: Re: 4.3bsd Usrptmap Message-ID: <24291@dog.ee.lbl.gov> Date: 1 Jul 92 15:27:38 GMT Article-I.D.: dog.24291 References: <l4et57INN34i@ack.cs.utexas.edu> Reply-To: torek@horse.ee.lbl.gov (Chris Torek) Organization: Lawrence Berkeley Laboratory, Berkeley Lines: 15 NNTP-Posting-Host: 128.3.112.15 In article <l4et57INN34i@ack.cs.utexas.edu> yau@cs.utexas.edu (King-Yeung Yau) writes: >Hi, In 4.3BSD Unix, there is a data structure called Usrptmap, which >is in addition to the user page tables. I don't quite understand the >purpose of this data structure. Why isn't it sufficient to allocate >only User page tables in kernel virtual address space using a resource >map? Usrptmap[] is the page table that maps the user page tables. This first-level page table must be in physically contiguous memory (per the VAX architecture). The easiest way to do that was to make it static duration. The kernel memory allocators do not arrange for contiguous physical pages. -- In-Real-Life: Chris Torek, Lawrence Berkeley Lab CSE/EE (+1 510 486 5427) Berkeley, CA Domain: torek@ee.lbl.gov