Re: filemap_fdatawait() wait_on_page_writeback_range(mapping, 0, -1)?

[Andrew Morton <akpm@osdl.org>]

Marcelo Tosatti <marcelo.tosatti@cyclades.com> wrote:
>
> Hi Andrew,
> 
> I dont understand why we do call wait_on_page_writeback_range() with -1 
> as the "end" argument.

"every page in the file".

> -1 sounds pretty stupid at first, it does unnecessary calls to 
> the radix lookup code.

I guess it could cause one extra call into the lookup code.  There's an
additional check in -mm's wait_on_page_writeback_range() which would prevent
that.

> --- a/mm/filemap.c.orig      2004-08-19 14:36:02.000000000 -0300
> +++ b/mm/filemap.c.isize     2004-08-19 18:17:14.000000000 -0300
> @@ -231,7 +231,7 @@
>   */
>  int filemap_fdatawait(struct address_space *mapping)
>  
> -       return wait_on_page_writeback_range(mapping, 0, -1);
> +       return wait_on_page_writeback_range(mapping, 0, i_size_read(mapping->host));
>  }

That would need a >> PAGE_CACHE_SHIFT