[MUD-Dev] Re: TECH: Distributed Muds

Vincent Archer archer at nevrax.com
Wed May 2 11:32:19 New Zealand Standard Time 2001


According to Matthew D. Fuller:

> BSD requires no such thing.  Most BSD manuals will tell you to
> configure at least double the swap as you have physical RAM, because
> for a very very long time, that was conventional wisdom for a
> starting figure, and it's still (IMO) a reasonable beginning
> approximation.  Of

Depend if you have modern or old BSD VM :)

The double swap space was a strong constraints on most BSD systems for
a long time because of a border bug that was never fixed. Namely, when
your system did panic for whatever reason, it would save the entire
memory as a crash dump... on the swap space.

The problem being that, it reserved a "reasonable space" so that the
dump would not be overwritten when the system restarted, before it got
around to save the dump to a file, and, since during a panic, a lot of
the data structures of the kernel are suspect, the dump code used a
single variable (the block number on disk where to start dumping).

Thus, if you didn't reserve over 150% of your ram for a swap space,
the first panic would happily overwrite the start of the next
partition (typically, the /usr file system, where all of the system
resides).

> None of this, however, translates to "needs more swap".  And get
> your terminology straight; ever *nix system on the market has at
> least as much 'VM' as RAM, since everything happens in VM; the VM
> sections are just mapped to physical RAM, or swap space, or nothing,
> etc, as

Or file space. Most moderns unices allow you to mmap, i.e. map a file
into memory. No more read/write: you merely put some pointers in it,
and access directly structures.

--
Vincent Archer                                         Email: archer at nevrax.com

Nevrax France.                              Off on the yellow brick road we go!
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