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SubjectRe: O_DIRECT question
Linus Torvalds wrote:
>
> On Thu, 11 Jan 2007, Aubrey wrote:
>
>>Now, my question is, is there a existing way to mount a filesystem
>>with O_DIRECT flag? so that I don't need to change anything in my
>>system. If there is no option so far, What is the right way to achieve
>>my purpose?
>
>
> The right way to do it is to just not use O_DIRECT.
>
> The whole notion of "direct IO" is totally braindamaged. Just say no.
>
> This is your brain: O
> This is your brain on O_DIRECT: .
>
> Any questions?
>
> I should have fought back harder. There really is no valid reason for EVER
> using O_DIRECT. You need a buffer whatever IO you do, and it might as well
> be the page cache. There are better ways to control the page cache than
> play games and think that a page cache isn't necessary.
>
> So don't use O_DIRECT. Use things like madvise() and posix_fadvise()
> instead.

OK, madvise() used with mmap'ed file allows to have reads from a file
with zero-copy between kernel/user buffers and don't pollute cache
memory unnecessarily. But how about writes? How is to do zero-copy
writes to a file and don't pollute cache memory without using O_DIRECT?
Do I miss the appropriate interface?

> Linus
> -
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