Alan Cox <alan@lxorguk.ukuu.org.uk> writes:
> > On September 17, 2001 06:03 pm, Eric W. Biederman wrote:
> > > In linux we have avoided reverse maps (unlike the BSD's) which tends
> > > to make the common case fast at the expense of making it more
> > > difficult to handle times when the VM system is under extreme load and
> > > we are swapping etc.
> >
> > What do you suppose is the cost of the reverse map? I get the impression you
>
> > think it's more expensive than it is.
>
> We can keep the typical page table cost lower than now (including reverse
> maps) just by doing some common sense small cleanups to get the page struct
> down to 48 bytes on x86
While there is a size cost I suspect you will notice reverse maps
a lot more in operations like fork where having them tripples the amount
of memory that you need to copy. So you should see a double or more
in the time it takes to do a fork.
That I think is a significant cost.
Eric
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This archive was generated by hypermail 2b29 : Sun Sep 23 2001 - 21:00:33 EST