Re: [PATCH] New phys_addr() syscall

Richard Gooch (Richard.Gooch@atnf.CSIRO.AU)
Tue, 21 Jul 1998 17:28:05 +1000

Raul Miller writes:
> Albert D. Cahalan <acahalan@cs.uml.edu> wrote:
> > There were plans to make mlock() available to normal users for
> > cryptographic purposes. There would be a quota to protect the
> > machine. If a user (or group of users) can get 1/32 of the pages
> > below 16 MB, then the system can not allocate 128 kB for DMA.
>
> You'll eventually want to allow memory locked with this variation of
> mlock to be migrated out of the DMA region (to deal with fragmentation
> issues).

That may present an unacceptable cost to a RT application. Copying a
page can easily take 100 microseconds. If Linux ever has the ability
to pin a RT process to a CPU, that process should never be delayed if
it doesn't ask to I/O (assuming it's mlock(2)ed all it's pages).

Moving to another physical page is contrary to the spirit of mlock(2),
IMO.

Regards,

Richard....

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