Re: Memory compression (again). . help?

[John Richard Moser <nigelenki@comcast.net>]

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Rik van Riel wrote:
> On Mon, 27 Feb 2006, John Richard Moser wrote:
> 
>> Hmm, I can't see where the kernel checks to see which pages are least
>> used. . . . anyone good with the VM can point me in the right direction?
> 
> Not completely written yet, but take a look at:
> 
> 	http://linux-mm.org/PageOutKswapd
> 

Wow nice.  Confusing, but nice.

I'm currently peeking around vmscan.c, though I can't seem to tell quite
how the kernel knows what's hot and cold.  I heard somewhere that when a
process doesn't use memory for like 5 days, the kernel knows better to
swap that instead of something it used 10 minutes ago.  I'm not sure how
though, I don't think the kernel debugs memory access.  My best guess is
when the page falls out of process TLB, the kernel is notified about it
and keeps these in order; and when it's faulted back into TLB, the
kernel is notified and moves it up to more recently used.  Of course,
this would mean the kernel never invalidates stuff in the process' TLB
(working set), which doesn't make sense.  Either way the inner workings
don't matter much to me; what I'm worried about is where it accounts for
this and more importantly what APIs it provides to query this information.

> 

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