Re: Why are memory-mapped storages read-only?

On Wed, 2 Sep 2009, Yann LeCun wrote:

> The mmap functionality was implemented to allow access to
> large data files without having to explicitely load them
> into RAM in advance. Back in the old days of Solaris, if
> you mmapped in read-only mode, the swapping system was
> smart enough to never swap out. Hence you would save
> a lot on disk (or network) bandwidth.
>
> Also, you really don't want a random bug in a Lush program
> to inadvertently corrupt your dataset file on disk......
>
> That said, we could have two types of mmapped storages:
> one for read only, and one for read/write.

That sounds like Solaris' swapping was a actually not
very smart if it swapped out untouched, writable pages.

Ok, I will look into it.

Ralf


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