Re: Completely new idea to virtual memory

Re: Completely new idea to virtual memory

[Chuck Ebbert]

>> Why not also write pages out to swap before it's really necessary?
>> If they were left mapped but marked as having up-to-date copies
>> on swap, they could be discarded immediately if the system needed
>> memory.  (Of course if they got written to they would have to be
>> paged out again.)
>
>Hmmm, interesting...


  The gains from this might be largely illusion but you could get some
theoretical benefits:

  o could write out lots of pages to swap without having to flush TLBs
    like you would if doing normal swap, since page remains present

  o if swsusp does not need to write already-backed pages it could
    reduce suspend time

  Maybe something like this?

   if about_to_spin_down_disks || swap_disk_idle
       if lots_of_memory_free
           page_in
       if little_memory_free
           copy_pages_to_swap
                  
 
--
 "Let's fight till six, and then have dinner," said Tweedledum.
  --Lewis Carroll, _Through the Looking Glass_

Re: Completely new idea to virtual memory

[Nigel Cunningham]

On Sat, 2003-04-12 at 21:52, Chuck Ebbert wrote: 
>   o if swsusp does not need to write already-backed pages it could
>     reduce suspend time

Hmmm. Not sure if it's worth the time taken to code & run figuring out
if it's already backed, though :>. Would we ever be talking about a
significant proportion of pages?

Regards,

Nigel

Re: Completely new idea to virtual memory

[John Bradford]

>   Maybe something like this?
> 
>    if about_to_spin_down_disks || swap_disk_idle
>        if lots_of_memory_free
>            page_in
>        if little_memory_free
>            copy_pages_to_swap

Exactly - plus, if the disk is only, or mainly, used for swap, you
could purposely spin it down after doing the speculative swapout.

John.

Re: Completely new idea to virtual memory

[Chuck Ebbert]

Nigel Cunningham wrote:


>>   o if swsusp does not need to write already-backed pages it could
>>     reduce suspend time
>
> Hmmm. Not sure if it's worth the time taken to code & run figuring out
> if it's already backed, though :>. Would we ever be talking about a
> significant proportion of pages?


  Depends on how aggressively you write them out, I guess.

  Is there even a way to write pages to swap without unmapping them?


--
 "Let's fight till six, and then have dinner," said Tweedledum.
  --Lewis Carroll, _Through the Looking Glass_