Re: frontswap/zcache: xvmalloc discussion

[Nitin Gupta <ngupta@vflare.org>]

On 06/24/2011 08:52 AM, Dave Hansen wrote:
> On Thu, 2011-06-23 at 23:11 -0700, Nitin Gupta wrote:
>> Much of this vpage functionality seems to be already present in mainline
>> as "flexible arrays"[1]
>
> That's a good observation.  I don't know who wrote that junk, but I bet
> they never thought of using it for this purpose. :)
>
> FWIW, for flex_arrays, the biggest limitation is that the objects
> currently can not cross page boundaries.  The current API also doesn't
> have any concept of a release function.  We'd need those to do the
> unmapping after a get().  It certainly wouldn't be impossible to fix,
> but it would probably make it quite a bit more complicated.
>
> The other limitation is that each array can only hold a small number of
> megabytes worth of data in each array.  We only have a single-level
> table lookup, and that first-level table is limited to PAGE_SIZE (minus
> a wee bit of metadata).
>

These limitations really makes them unsuitable for use in the new 
allocator and I guess "fixing" them is also not a good idea -- if its 
fundamentally designed to work on small number of objects, it should 
probably be left as-is.  Not sure who really uses flex arrays?

So, if and when vpage stuff is introduced, existence of flex_arrays 
should not become a barrier.

Thanks,
Nitin

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>