Re: [coreutils] [PATCH] fadvise: new module providing a simpler interface to posix_fadvise

[Jim Meyering]

Pádraig Brady wrote:

> To get the same benefits noticed with `sort`
> http://git.savannah.gnu.org/gitweb/?p=coreutils.git;a=commit;h=dae35bac
> I'm applying the same hint to all appropriate utils in the attached.
...

> Linux does quite well without this hint, and is getting better:
>   http://article.gmane.org/gmane.linux.kernel.mm/43753
>   http://lkml.org/lkml/2010/2/3/27
> However I saw a small benefit on my system with
> fast flash devices (around 5% less run time) and perhaps

Nice!

> the kernel can use this info in more sophisticated ways in future.
...
> diff --git a/src/wc.c b/src/wc.c
...
> @@ -211,6 +212,10 @@ wc (int fd, char const *file_x, struct fstatus *fstatus)
>      }
>    count_complicated = print_words || print_linelength;
>
> +  /* Only advise the kernel of our access pattern if we need to read().  */
> +  if (!count_bytes || count_chars || print_lines || count_complicated)
> +    fdadvise (fd, 0, 0, FADVISE_SEQUENTIAL);
> +
...


If you reword that comment

   /* Advise the kernel of our access pattern only if we will read().  */

it won't imply that advising is all it does in that case.