On Fri, 2 Dec 2005, Timothy A. Chagnon wrote:
Maybe since you have a small amount of memory in that machine, when
you do the copy, the disk buffer gets filled with the blocks from the
file you are copying. Other applications with open files no longer
have their blocks in the disk buffer, so they have to wait in line for
disk access.
the two activities were
o disk to disk copy
o fetch webpage with 10M of images over network
I guess the 10M could be pushed to swap, but when I change
screens and then back again, the images are still there (and
don't have to be loaded from swap). I assume then that these
two activities are orthogonal (that was the intention at
least).
I did some googling and found a few items about possible ways to skip
the disk buffer and asynchronous I/O (AIO, libaio1):
http://lse.sourceforge.net/io/aio.html
http://www.oracle.com/technology/pub/columns/talkinglinux_0104.html
These imply that with AIO, it is possible to open a file (via the
open(2) function) with the O_DIRECT flag, thus bypassing the disk
buffer. Googling for this, there are a lot of mailing list threads
about dd having different command line options to use this.
dd conv=direct
dd iflags=direct oflags=direct
dd o_direct=yes
dd --o_direct=512,1024
OK will give these a try. I first looked at all these flags
when I was first learning unix and went "groan" and have not
thought about them since.
As for reprogramming tools to do file copies; I was hoping
not to have to do this. For the moment, I'll just put up
with the slowdown.
Oh, well. Maybe just try the dd commands or try to get a copy with
those options. Interesting though.
I don't see why a copy need flush all of memory by default.
A copy only needs enough memory (which can't be a whole lot)
and not ask for any more.
Thanks for the ideas
Joe
--
Joseph Mack NA3T EME(B,D), FM05lw North Carolina
jmack (at) wm7d (dot) net - azimuthal equidistant map
generator at http://www.wm7d.net/azproj.shtml
Homepage http://www.austintek.com/ It's GNU/Linux!
--
TriLUG mailing list : http://www.trilug.org/mailman/listinfo/trilug
TriLUG Organizational FAQ : http://trilug.org/faq/
TriLUG Member Services FAQ : http://members.trilug.org/services_faq/
