RE: Speeding up swap

David Schwartz (davids@webmaster.com)
Sun, 24 Oct 1999 15:24:51 -0700

> On Sun, Oct 24, 1999 at 11:40:26AM -0700, David Schwartz wrote:
>
> > Then one the file twice. With one fd, you can do your
> buffered, random
> > accesses. With the other fd, you can do your non-buffered, sequential
> > accesses.
>
> wouldn't that defeat the purpose of restricting lseek? a malicious program
> could just open the file twice.

No, because the file descriptor that they could seek on would be subject to
normal buffering rules. The feature being discussed is _per_fd_ control over
caching of buffers. So the malicious program could not force the hardware to
keep rereading the same small set of pages.

Of course, a malicious program could cause the hardware to keep rereading
the same _large_ set of pages, but they can do that now. And this would
minimize the harm that would do, because it at least wouldn't blow out the
buffer cache.

DS

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