George Neuner <firstname.lastname@example.org> wrote:
| I don't think it's possible in most current OSes to bypass the file
| cache when reading using standard I/O calls.
But note than many current operating systems, expecially those that
support high-performance filesystems like XFS (which includes Irix
and Linux, at a minimum), provide an O_DIRECT mode bit in "open()"
which *does* bypass the cache. From "man 2 open" on Linux:
Try to minimize cache effects of the I/O to and from this file.
In general this will degrade performance, but it is useful in
special situations, such as when applications do their own
caching. File I/O is done directly to/from user space buffers.
The I/O is synchronous, i.e., at the completion of the read(2)
or write(2) system call, data is guaranteed to have been trans-
ferred. Under Linux 2.4 transfer sizes, and the alignment of
user buffer and file offset must all be multiples of the logical
block size of the file system. Under Linux 2.6 alignment to
512-byte boundaries suffices.
A semantically similar interface for block devices is described
Rob Warnock <email@example.com>
627 26th Avenue <URL:http://rpw3.org/>
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