Re: O_DIRECT question
From: Phillip Susi
Date: Thu Jan 11 2007 - 18:01:53 EST
Michael Tokarev wrote:
Linus Torvalds wrote:
On Thu, 11 Jan 2007, Viktor wrote:
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?
mmap()+msync() can do that too.
It can, somehow... until there's an I/O error. And *that* is just terrbile.
The other problem besides the inability to handle IO errors is that
mmap()+msync() is synchronous. You need to go async to keep the
pipelines full.
Now if someone wants to implement an aio version of msync and mlock,
that might do the trick. At least for MMU systems. Non MMU systems
just can't play mmap type games.
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