From owner-freebsd-hackers Thu Aug 1 09:07:09 1996 Return-Path: owner-hackers Received: (from root@localhost) by freefall.freebsd.org (8.7.5/8.7.3) id JAA22525 for hackers-outgoing; Thu, 1 Aug 1996 09:07:09 -0700 (PDT) Received: from axp5.physik.fu-berlin.de (axp5.fddi5B.fu-berlin.de [160.45.5.75]) by freefall.freebsd.org (8.7.5/8.7.3) with ESMTP id JAA22513 for ; Thu, 1 Aug 1996 09:07:03 -0700 (PDT) Received: from mordillo (graichen.dialup.fu-berlin.de [160.45.217.183]) by axp5.physik.fu-berlin.de (8.7.1/8.7.1) with ESMTP id SAA16381 for ; Thu, 1 Aug 1996 18:06:58 +0200 (MET DST) Received: (from graichen@localhost) by mordillo (8.6.12/8.6.12) id SAA01016 for hackers@FreeBSD.org; Thu, 1 Aug 1996 18:01:34 +0200 From: Thomas Graichen Message-Id: <199608011601.SAA01016@mordillo> Subject: vm questions To: hackers@FreeBSD.org Date: Thu, 1 Aug 1996 18:01:33 +0200 (MET DST) X-Mailer: ELM [version 2.4 PL24] Content-Type: text Sender: owner-hackers@FreeBSD.org X-Loop: FreeBSD.org Precedence: bulk i'm currently reading "the design & implementation ..." as some kind of relaxation to all the learning for my physics examinations and have some questions about the vm stuff - can someone - john or david - or maybe someone else please look at them ? * on page 145 is written: "a limitation of the implementation is that it cannot collaps two objects if either of them has allocated a pager. this limitation is serious, since pagers are allocated when the system begins running short of memory -- precisely the time when reclaiming of memory from collapsed objects is most necesarry." - is this the swap leaking bug in the original 4.4 BSD vm system ? - how is this problem avoided by the FreeBSD vm system ? (it was from the chapter "collapsing of shadow chains") * on page 158 is written: "a more consistent interface can be obtained by using a common cache for both the virtual-memory system and the filesystem. three approaches to merging the two caches are being undertaken. one approach is to have the filesystem use objects in the virtual-memory system as its cache; a second approach is to have the virtual-memory objects that map files use the existing filesystem cache; the third approach is to create a new cache that is a merger of the two existing caches, and to convert both the virtual memory and the filesystems to use this new cache. each of these approaches has its merits and drawbacks; it is not yet clear which approach will work best." (this is from the chapter "vnode pager") - my questions here are: which of the three ways is implemented in FreeBSD ? - which are implemented in other operating systems (linux, sunos, digital unix, etc.) ? * can anyone please write some lines about the basic changes to the vm-system in FreeBSD (so that i can understand it :-) - i don't know much about the kernel stuff other than reading the mailinglists and commit-messages - but i think i understand whats written in the above book - i hope at least partially :-) - it would also be interesting to get some feeling for the fork/exec/pipe changes ? would be nice if someone could scribble something down about it - so that my couriosity after reading the book is satsified :-) - a lot of thanks in advance t p.s.: and one last question - what is the state of 4.4 BSD ? - in the book it is said that lite 2 was really the last one - but from some mailinglists it sounds that kirk and maybe others are heavily working on filesystems etc. - will there be something like lite 3 ? p.s.2.: by the way - the book is very good - at least for people like who can learn a lot by reading it - i highly recommend it -> "the design and implementation of the 4.4 BSD operating system" -- thomas graichen graichen@mail.physik.fu-berlin.de graichen@FreeBSD.org perfection is reached, not when there is no longer anything to add, but when there is no longer anything to take away antoine de saint-exupery