Re: [PATCH 4/7][TAKE5] support new modes in fallocate

Nathan Scott
2007-06-28T00:54:16Z

On Thu, 2007-06-28 at 10:39 +1000, David Chinner wrote:
>
>
> I don't think it does - swapfile I/O looks like it goes direct to
> bio without passing through the filesystem. When the swapfile is
> mapped, it scans and records the extent map of the entire swapfile
> in a separate structure and AFAICT the swap code uses that built map
> without touching the filesystem at all.
>
> If that is true then the written/unwritten state of the extents is
> irrelevant; all we need is allocated disk space for the file and
> swapping should work. And it's not like anyone should be reading
> the contents of that swapfile through the filesystem, either. ;)

Ah, yes, good point - thats true. Unwritten extents are ideal for
this then, as attempts to read swap via the regular interfaces will
return zeros instead of random swapped out memory contents.

cheers.