cp uses mmap() to copy files < 8MB. When files are copied from the local host to a remote box via NFS data is transferred very slowly. For bigger files, cp uses read() and write() alternately which performs very well. Fix: I have no idea. FreeBSD-4 uses the same mmap() thingy in utils.c and here performance is ok so I assume the problem is somewhere else than in the cp sources. How-To-Repeat: I have two files, one is 6MB in size and the other one is 12MB. I copy them from the local box to an NFS mounted directory named /scratch: andre@bali:/tmp>time cp 12mb /scratch cp 12mb /scratch 0.00s user 0.12s system 10% cpu 1.142 total andre@bali:/tmp>time cp 6mb /scratch cp 6mb /scratch 0.00s user 0.13s system 0% cpu 14.274 total The 12MB filecopy performs quite well as I would expect it from a 100MBit network. The 6mb filecopy I won't comment on :-). (This is an extreme case, other client-server combinations are faster. The "fastest" one I found was 4 seconds which is still bad for a 6MB file). In the mmap() case, the whole source file is mmap'ed and one write() call is used which tries to write the whole file all at once. I have modified copy_file() in utils.c in a way that instead of one "big" write(), several small ones are being made (this is no fix, just for demonstration): --- utils.c.ORI Thu Aug 19 07:04:27 2004 +++ utils.c Fri Oct 21 18:19:59 2005 @@ -140,7 +140,11 @@ wtotal = 0; for (bufp = p, wresid = fs->st_size; ; bufp += wcount, wresid -= (size_t)wcount) { +#if 0 wcount = write(to_fd, bufp, wresid); +#else + wcount = write(to_fd, bufp, wresid > 65536 ? 65536 : wresid ); +#endif wtotal += wcount; if (info) { info = 0; 65536 is just a value for playing; almost everything below 1M and not ridiculous small will do it: andre@bali:/tmp>time cp 6mb /scratch cp 6mb /scratch 0.00s user 0.05s system 8% cpu 0.618 total
Try the following: In bin/cp/utils.c (source) there is a check, if the file is less than 8MB or so, it uses mmap, if the file is larger, it will use write() Modify the source and recompiled to -never- use mmap, only to use write() Change line 143: original: fs->st_size <= 8 * 1048576) { New: fs->st_size <= 8 * 8) { It will use mmap still if the file is larger than 64bytes (if it uses bytes there, pretty sure it does). This is from a response to the freebsd-stable mailing list back in 2009 by Brent Jones he reported a 100 fold increase.
I even went a step further an simply Undef'ed VM_AND_BUFFER_CACHE_SYNCHRONIZED in cp's Makefile so the entire mmap code gets disabled...
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