Re: [PATCH] Use a hash rather than a linked-list for cycle check in cp

[Jim Meyering]

"Bo Borgerson" <address@hidden> wrote:
> This addresses a FIXME in src/copy.c:
>
> ----
> -/* FIXME: rewrite this to use a hash table so we avoid the quadratic
> -   performance hit that's probably noticeable only on trees deeper
> -   than a few hundred levels.  See use of active_dir_map in remove.c  */
> ----
>
> The performance benefit is there, but on my machine with a PATH_MAX of
> 4096 it's hard to see, because the userland work `cp' does is dwarfed
> by the work the kernel does on its behalf:
>
> ----
> $ time src/cp.master -r a b
>
> real    0m54.032s
> user    0m3.236s    <-- coreutils HEAD
> sys     0m47.335s
>
> $ time src/cp -r a c
>
> real    0m53.475s
> user    0m0.624s    <-- with patch
> sys     0m48.639s
> ----

Hi Bo,

Thanks for that patch.

However, let's see if Cai Xianchao and Li Zefan
are still working on rewriting cp to use openat-style functions.

  http://thread.gmane.org/gmane.comp.gnu.coreutils.bugs/12041

Because once cp is rewritten the way I outlined later in
that thread, there will be no need for your patch.

By the way, I do still plan to add a --total option to df.
Li Zefan revived an old patch to that effect, but it needs
some work and perhaps a test or two.