On Mon, 16 Oct 2000, Andrea Arcangeli wrote:
>
> If the page isn't locked swap_out will unmap it from the pte and anybody will
> be able to start any kind of regular VM I/O on the page.
Doesn't matter.
If you have increased the page count, the page _will_ stay in the page
cache. So everybody who wants to see the page that was mapped, will see it
with no possibility of getting an alias.
> This isn't what the
> programmer expects
If so, the programmer has shit for brains. That simple.
> and that's not what I consider pinning.
No. Because "pinning" is _stupid_.
Imagine having two threads that both do direct IO from overlapping pages.
YOU NEED TO COUNT THE PINNING.
A "lock" bit is useless, and anybody who uses a lock bit is stupid and
ends up having to serialize things for no good reason.
Instead, the Linux answer is to say: pinning is bad, pinning is stupid,
pinning is useless - so dont do it.
Instead, we have the notion of "I have a reference to this page, don't let
it go away". Sure, the page can be _unmapped_ (ie it is not pinned), but
WHO CARES?
Nobody.
Linus
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