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SubjectRe: O_DIRECT question


On Wed, 10 Jan 2007, Linus Torvalds wrote:
>
> So don't use O_DIRECT. Use things like madvise() and posix_fadvise()
> instead.

Side note: the only reason O_DIRECT exists is because database people are
too used to it, because other OS's haven't had enough taste to tell them
to do it right, so they've historically hacked their OS to get out of the
way.

As a result, our madvise and/or posix_fadvise interfaces may not be all
that strong, because people sadly don't use them that much. It's a sad
example of a totally broken interface (O_DIRECT) resulting in better
interfaces not getting used, and then not getting as much development
effort put into them.

So O_DIRECT not only is a total disaster from a design standpoint (just
look at all the crap it results in), it also indirectly has hurt better
interfaces. For example, POSIX_FADV_NOREUSE (which _could_ be a useful and
clean interface to make sure we don't pollute memory unnecessarily with
cached pages after they are all done) ends up being a no-op ;/

Sad. And it's one of those self-fulfilling prophecies. Still, I hope some
day we can just rip the damn disaster out.

Linus
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