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

Nai Xia nai.xia at gmail.com
Tue Jun 17 01:51:11 EDT 2008

So, we are free to invade the kernel, now :)

On Mon, Jun 16, 2008 at 9:33 PM, Nitin Gupta <nitingupta910 at gmail.com> wrote:
> On Mon, Jun 16, 2008 at 6:33 PM, John McCabe-Dansted <gmatht at gmail.com> wrote:
>> 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?
> Yes, that's true.
>> 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?)
> This unlikely() will not be good for compcache so, cleanly introducing
> ifdef (via some wrapper that's noop without compcache) sounds better.
> I will post this on LKML to get more feedback on this.
> Overall, with this notify thing, compcache is now just so good :)
> Nitin
>> * 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
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