Re: VM tuning patch, take 2

[Rik van Riel <riel@conectiva.com.br>]

On Thu, 7 Jun 2001, Jonathan Morton wrote:

> - ageing is now done evenly, and independently of the number of
> mappings on a given page.  This is done by introducing a 4th LRU list
> (aside from active, inactive_clean and inactive_dirty) which holds
> pages attached to a process but not in the swapcache.

IMHO it would be better to add these to the active list so both
filesystem-backed and swap-backed pages will be aged the same.

> - try_to_swap_out() will now refuse to move a page into the swapcache
> which still has positive age.  This helps preserve the working set
> information, and may help to reduce swap bloat.  It may re-introduce
> the cause of cache collapse, but I haven't seen any evidence of this
> being disastrous, as yet.

This should only affect swap bloat and nothing else. The "cache
collapse" thing vmstat might show is just a "lack" of swap cache
pages being generated...

> - new pages are still given an age of PAGE_AGE_START, which is 2.
> PAGE_AGE_ADV has been increased to 4, and PAGE_AGE_MAX to 128.  Pages which
> are demand-paged in from swap are given an initial age of PAGE_AGE_MAX/2,
> or 64 - this should help to keep these (expensive) pages around for as long
> as possible.  Ageing down is now done using a decrement instead of a
> division by 2, preserving the age information for longer.

I think the PAGE_AGE_START should be the same for all pages.
About decrement vs. division by two, I think this is something
we may want to make tunable (I have the code for this floating
around somewhere, hold on).


regards,

Rik
--
Virtual memory is like a game you can't win;
However, without VM there's truly nothing to lose...

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