Messages in this thread | | | Date | Fri, 12 Jan 2007 20:03:15 +0300 | From | Viktor <> | Subject | Re: O_DIRECT question |
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Linus Torvalds wrote: >>>>O_DIRECT is still crazily racy versus pagecache operations. >>> >>>Yes. O_DIRECT is really fundamentally broken. There's just no way to fix >>>it sanely. >> >>How about aliasing O_DIRECT to POSIX_FADV_NOREUSE (sortof) ? > > > That is what I think some users could do. If the main issue with O_DIRECT > is the page cache allocations, if we instead had better (read: "any") > support for POSIX_FADV_NOREUSE, one class of reasons O_DIRECT usage would > just go away. > > See also the patch that Roy Huang posted about another approach to the > same problem: just limiting page cache usage explicitly. > > That's not the _only_ issue with O_DIRECT, though. It's one big one, but > people like to think that the memory copy makes a difference when you do > IO too (I think it's likely pretty debatable in real life, but I'm totally > certain you can benchmark it, probably even pretty easily especially if > you have fairly studly IO capabilities and a CPU that isn't quite as > studly). > > So POSIX_FADV_NOREUSE kind of support is one _part_ of the O_DIRECT > picture, and depending on your problems (in this case, the embedded world) > it may even be the *biggest* part. But it's not the whole picture.
From 2.6.19 sources it looks like POSIX_FADV_NOREUSE is no-op there
> Linus
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