Re: [lc-devel] vswap patch

[Nitin G. <nit...@gm...>]

Hi Allan,

On 6/24/06, Allan Bezerra <all...@gm...> wrote:
>
> > I didn't let print anything for vswap when reading /proc/swaps (please
> see: swap_show() in swapfile.c).
>
> Cool! Now, I understanding that. However, I think that show only summary
> line isn't good. Therefore, we can change the summary print order seq_puts(swap,
> "Filename\t\t\t\tType\t\tSize\tUsed\tPriority\n") to after SWP_COMPRESSED
> check. See the patch attached.
>
> Please, feel free to accept this suggestion.
>

diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 2c439eb..a43bb9f 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -1269,14 +1269,14 @@ static int swap_show(struct seq_file *sw
>         struct file *file;
>         int len;
>
> -       if (v == swap_info)
> -               seq_puts(swap,
> "Filename\t\t\t\tType\t\tSize\tUsed\tPriority\n");
> -
>         if (ptr->flags & SWP_COMPRESSED) {
>                 pr_info("vswap to be printed\n");
>                 return 0;
>         }
>
> +       if (v == swap_info)
> +               seq_puts(swap,
> "Filename\t\t\t\tType\t\tSize\tUsed\tPriority\n");
> +
>         file = ptr->swap_file;
>         len = seq_path(swap, file->f_vfsmnt, file->f_dentry, " \t\n\\");
>         seq_printf(swap, "%*s%s\t%u\t%u\t%d\n",
>


This patch has a problem. It will not print heading if vswap is enabled
before any other swap. So, patch will be:

diff --git a/mm/swapfile.c b/mm/swapfile.c
index a5461ef..a1d4af6 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -1329,13 +1329,15 @@ static int swap_show(struct seq_file *sw
        struct file *file;
        int len;

+       if (ptr->flags & SWP_COMPRESSED) {
+               pr_info("swap_show: vswap to be printed\n");
+               if (ptr->next == -1) return 0;
+       }
+
        if (v == swap_info)
                seq_puts(swap,
"Filename\t\t\t\tType\t\tSize\tUsed\tPriority\n");

-       if (ptr->flags & SWP_COMPRESSED) {
-               pr_info("vswap to be printed\n");
-               return 0;
-       }
+       if (ptr->flags & SWP_COMPRESSED) return 0;

        file = ptr->swap_file;
        len = seq_path(swap, file->f_vfsmnt, file->f_dentry, " \t\n\\");


Outputs:

problem with your patch:
[root@localhost ~]# cat /proc/swaps
[root@localhost ~]# echo "10" > /proc/sys/vm/max_anon_cc_size
[root@localhost ~]# cat /proc/swaps
[root@localhost ~]# swapon /dev/sda2
[root@localhost ~]# cat /proc/swaps  *** no heading ***
/dev/sda2                               partition       530136  0       -1
[root@localhost ~]#

with second patch:

[root@localhost ~]# cat /proc/swaps
[root@localhost ~]# echo "10" > /proc/sys/vm/max_anon_cc_size
[root@localhost ~]# cat /proc/swaps
[root@localhost ~]# swapon /dev/sda2
[root@localhost ~]# cat /proc/swaps ** heading back **
Filename                                Type            Size    Used
Priority/dev/sda2                               partition       530136
0       -1
[root@localhost ~]#

and it does't print anything when there's only vswap enabled (as expected).
I will soon push this in master branch...

Thanks for making me aware of this problem :)

Cheers,
Nitin Gupta