[linux-mm-cc] compcache with swap free notify support

[John McCabe-Dansted]

On Mon, Jun 16, 2008 at 4:59 PM, Nitin Gupta <nitingupta910 at gmail.com> wrote:
> Hi All,
>
> Attached is the patch for much refined version of compcache (for
> kernel 2.6.26-rc6). This version saves lot more memory than previous
> versions since it now know when a swap page is no longer in use. So,

Just to clarify, there could still be two copies of the page if the
page is clean but not free?

Notification that a page is free could be useful in other cases as
well. E.g. if you are in a VM with dynamic partitions, it could be
useful for ext4 to tell the VM that some sectors are no longer
required.

Also just to comment on "the colour of the bikeshed"*
                       if (p->notify_swap_entry_free_fn)
could perhaps be
                       if (unlikely(p->notify_swap_entry_free_fn))
to minimize the effect of this change on people who don't need it,
until compcache enters widespread use.
Also the line could be #ifdef'd out if it is not in use (but the
kernel folks don't like ifdefs?)

* The cost of a single branch is probably insignificant compared to
the cost of swap (including disk access), but everyone likes to voice
an opinion :) (and now you know some one has at least skimmed the
code)

>  - In kernel config, enable (as module or in-built): Device Drivers

You can also just do a "make oldconfig" and hit the 'y' key several times.

-- 
John C. McCabe-Dansted
PhD Student
University of Western Australia