Official request: Please make GNU grep the default
kostikbel at gmail.com
Tue Aug 17 15:47:14 UTC 2010
[Cc: list sanitized]
On Tue, Aug 17, 2010 at 05:28:08PM +0200, Dimitry Andric wrote:
> On 2010-08-16 10:55, Dag-Erling Sm??rgrav wrote:
> > Dimitry Andric <dimitry at andric.com> writes:
> >> - Uses plain file descriptors instead of struct FILE, since the
> >> buffering is done manually anyway, and it makes it easier to support
> >> gzip and bzip2.
> > It might be worth a shot adding mmap(2) support as well, i.e. when
> > processing an uncompressed regular file, try to mmap(2) it first, and if
> > that fails, fall back to the plain buffered read(2) method.
> I added a simple mmap to grep, and time-trialed it, but the mmap version
> was somewhat slower than the regular version. I understood from Kostik
> Belousov that readahead does not work properly with mmap, and it should
> not be used for "one-time" reads.
This is not exactly what I said. I argue that read-ahead implemented
by vm_faul() is much less efficient that buffer clustering. Also,
the cost of setting user mapping for the one time read is also non-trivial.
The conclusion is right, it is better to use read(2) for one-time read.
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