Re: [announce] swap mini-howto

[Andrew Morton]

Jeff Garzik wrote:
> 
> ...
> That said, I would like to again point out that using sparse swapfiles
> should still be discouraged.  It may be supported, but it's much better
> for system performance and stability, IMO, if the sysadmin makes certain
> all swapfiles are 100% allocated before they are mentioned to the swap
> subsystem.
> 

That got stamped out.  swapon will fail if the file isn't fully
instantiated on disk:

static int setup_swap_extents(struct swap_info_struct *sis)
{
	...
                        block = bmap(inode, probe_block + block_in_page);
                        if (block == 0)
                                goto bad_bmap;
	...

bad_bmap:
        printk(KERN_ERR "swapon: swapfile has holes\n");
        ret = -EINVAL;
}