Date: Thu, 1 Aug 1996 18:01:33 +0200 (MET DST) From: Thomas Graichen <graichen@axp5.physik.fu-berlin.de> To: hackers@FreeBSD.org Subject: vm questions Message-ID: <199608011601.SAA01016@mordillo>
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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
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