Messages in this thread | | | Subject | Re: mmap vs. O_DIRECT | From | Robert Love <> | Date | Thu, 11 Nov 2004 12:13:39 -0500 |
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On Thu, 2004-11-11 at 10:41 -0500, Robert Love wrote:
> There is a difference between being synchronous and not going through > the page cache, although in Linux we don't really have the distinction.
Rereading this, I should clarify. We definitely have the distinction.
In the case of direct I/O, you get synchronousness, no page caching, and no use of buffers. In my statement, I meant that you cannot separate the "no page cache" from the "synchronousness" attribute.
But you can get synchronous I/O and still get the page cache, ala O_SYNC.
The closest you can come to normal I/O without the page cache is by doing posix_fadvise() to prune your cache pages after you touch them. That is definitely not what you want.
Robert Love
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